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IETF RFC 7900
Last modified on Wednesday, June 22nd, 2016
 Permanent link to RFC 7900
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Internet Engineering Task Force (IETF) Y. Rekhter, Ed.
Request for Comments: 7900 E. Rosen, Ed.
Updates: 6513, 6514, 6625 Juniper Networks, Inc.
Category: Standards Track R. Aggarwal
ISSN: 2070-1721 Arktan
Y. Cai
Alibaba Group
T. Morin
Orange
June 2016
Extranet Multicast in BGP/IP MPLS VPNs
 Abstract
Previous RFCs specify the procedures necessary to allow IP multicast
traffic to travel from one site to another within a BGP/MPLS IP VPN
(Virtual Private Network). However, it is sometimes desirable to
allow multicast traffic whose source is in one VPN to be received by
systems that are in another VPN. This is known as a "Multicast VPN
(MVPN) extranet". This document updates RFCs 6513, 6514, and 6625 by
specifying the procedures that are necessary in order to provide
extranet MVPN service.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7900.
Rekhter, et al. Standards Track PAGE 1 
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................4
1.1. Terminology ................................................4
1.2. Scope ......................................................7
1.2.1. Customer Multicast Control Protocols ................7
1.2.2. Provider Multicast Control Protocols ................7
1.3. Clarification on Use of Route Distinguishers ...............8
1.4. Overview ...................................................9
2. Extranets and Overlapping Address Spaces .......................12
2.1. Ambiguity: P-Tunnel with Extranet/Non-extranet Flows ......14
2.2. Ambiguity: P-Tunnel with Multiple Extranet Flows ..........16
2.3. Preventing Misdelivery in These Scenarios .................18
2.3.1. Do Not Deliver Packets from the Wrong P-tunnel .....18
2.3.2. Policies to Prevent Ambiguity on a P-Tunnel ........20
3. Extranet Transmission Models ...................................21
3.1. Transmitting an Extranet C-Flow on a Single PMSI ..........21
3.1.1. Without Extranet Separation ........................22
3.1.2. With Extranet Separation ...........................22
3.2. Transmitting an Extranet C-Flow over Multiple PMSIs .......23
4. Distribution of Routes That Match C-S/C-RP Addresses ...........23
4.1. UMH-Eligible Routes .......................................23
4.1.1. Extranet Separation ................................24
4.2. Distribution of Unicast Routes Matching C-RPs and DRs .....25
4.3. Route Targets and Ambiguous UMH-Eligible Routes ...........26
4.4. Dynamically Marking Extranet Routes .......................27
4.4.1. The Extranet Source Extended Community .............27
4.4.2. Distribution of Extranet Source Extended
Community ..........................................29
4.5. The Extranet Separation Extended Community ................30
Rekhter, et al. Standards Track PAGE 2
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
5. Origination and Distribution of BGP A-D Routes .................30
5.1. Route Targets of UMH-Eligible Routes and A-D Routes .......30
5.2. Considerations for Particular Inclusive Tunnel Types ......33
5.2.1. RSVP-TE P2MP or Ingress Replication ................33
5.2.2. Ingress Replication ................................34
6. When PIM Is the PE-PE C-Multicast Control Plane ................35
6.1. Provisioning VRFs with RTs ................................36
6.1.1. Incoming and Outgoing Extranet RTs .................36
6.1.2. UMH-Eligible Routes and RTs ........................37
6.1.3. PIM C-Instance Reverse Path Forwarding
Determination ......................................37
6.2. "Single PMSI per C-Flow" Model ............................38
6.2.1. Forming the MI-PMSIs ...............................38
6.2.2. S-PMSIs ............................................41
6.2.3. Sending PIM Control Packets ........................42
6.2.4. Receiving PIM Control Packets ......................43
6.2.5. Sending and Receiving Data Packets .................43
6.3. "Multiple PMSIs per C-Flow" Model .........................43
6.3.1. Forming the MI-PMSIs ...............................44
7. When BGP Is the PE-PE C-Multicast Control Plane ................46
7.1. Originating C-Multicast Routes ............................46
7.2. Originating A-D Routes without Extranet Separation ........47
7.2.1. Intra-AS I-PMSI A-D Routes .........................47
7.2.2. S-PMSI A-D Routes ..................................47
7.2.3. Source Active A-D Routes ...........................48
7.2.3.1. When Inter-Site Shared Trees Are Used .....48
7.2.3.2. When Inter-Site Shared Trees Are
Not Used ..................................49
7.3. Originating A-D Routes with Extranet Separation ...........49
7.3.1. Intra-AS I-PMSI A-D Routes .........................49
7.3.2. S-PMSI A-D Routes ..................................50
7.3.3. Source Active A-D Routes ...........................52
7.4. Determining the Expected P-Tunnel for a C-Flow ............52
7.4.1. (C-S,C-G) S-PMSI A-D Routes ........................54
7.4.2. (C-S,C-*) S-PMSI A-D Routes ........................54
7.4.3. (C-*,C-G) S-PMSI A-D Routes ........................55
7.4.4. (C-*,C-*) S-PMSI A-D Routes ........................56
7.4.5. I-PMSI A-D Routes ..................................56
7.5. Packets Arriving from the Wrong P-Tunnel ..................57
8. Multiple Extranet VRFs on the Same PE ..........................57
9. IANA Considerations ............................................58
10. Security Considerations .......................................59
11. References ....................................................61
11.1. Normative References .....................................61
11.2. Informative References ...................................62
Acknowledgments ...................................................64
Contributors ......................................................64
Authors' Addresses ................................................65
Rekhter, et al. Standards Track PAGE 3
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
1. Introduction
Previous RFCs [RFC 6513] [RFC 6514] specify the procedures necessary to
allow IP multicast traffic to travel from one site to another within
a BGP/MPLS IP VPN (Virtual Private Network). However, it is
sometimes desirable to allow multicast traffic whose source is in one
VPN to be received by systems that are in another VPN. This is known
as an "extranet Multicast VPN (MVPN)". This document specifies the
procedures that are necessary in order to provide extranet MVPN
functionality.
This document updates RFCs 6513, 6514, and 6625 by specifying the
procedures that are necessary in order to provide extranet MVPN
service.
1.1. Terminology
This document uses terminology from [RFC 6513] and in particular uses
the prefixes "C-" and "P-" as specified in Section 3.1 of [RFC 6513],
and "A-D routes" for "auto-discovery routes".
The term "Upstream Multicast Hop" (UMH) is used as defined in
[RFC 6513].
The term "UMH-eligible route" is used to mean "route eligible for UMH
determination", as defined in Section 5.1.1 of [RFC 6513]. We will
say that a given UMH-eligible route or unicast route "matches" a
given IP address, in the context of a given Virtual Routing and
Forwarding table (VRF), if the address prefix of the given route is
the longest match in that VRF for the given IP address. We will
sometimes say that a route "matches" a particular host if the route
matches an IP address of the host.
We follow the terminology of Section 3.2 of [RFC 6625] when talking of
a "Selective Provider Multicast Service Interface" (S-PMSI) A-D route
being "installed". That is, we say that an S-PMSI A-D route is
"installed" (in a given VRF) if it has been selected by the BGP
decision process as the preferred route for its Network Layer
Reachability Information (NLRI). We also follow the terminology of
Section 3.2 of [RFC 6625] when saying that an S-PMSI A-D route has
been "originated by a given PE"; this means that the given Provider
Edge's (PE's) IP address is contained in the Originating Router's IP
Address field in the NLRI of the route.
Rekhter, et al. Standards Track PAGE 4
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
We use the following additional terminology and notation:
o Extranet C-source: a multicast source, in a given VPN, that is
allowed by policy to send multicast traffic to receivers that are
in other VPNs.
o Extranet C-receiver: a multicast receiver, in a given VPN, that is
allowed by policy to receive multicast traffic from extranet
C-sources that are in other VPNs.
o Extranet C-flow: a multicast flow (with a specified C-source
address and C-group address) with the following properties: its
source is an extranet C-source, and it is allowed by policy to
have extranet C-receivers.
o Extranet C-group: a multicast group address that is in the
"Any-Source Multicast" (ASM) group address range and that is
allowed by policy to have extranet C-sources and extranet
C-receivers that are not all in the same VPN. Note that we will
sometimes refer to "Source-Specific Multicast (SSM) C-group
addresses" (i.e., C-group addresses in the SSM group address
range) but will never call them "extranet C-groups".
N.B.: Any source of traffic for an extranet C-group is considered
to be an extranet C-source, and any receiver of traffic addressed
to an extranet C-group is considered to be an extranet C-receiver.
o Extranet C-RP: a multicast Rendezvous Point (RP) for an extranet
C-group; it is allowed by policy to receive PIM Register messages
[RFC 7761] from outside its VPN and to send multicast data packets
to extranet C-receivers outside its VPN.
o Host(C-S,A): the host (or, if C-S is an "anycast address", the set
of hosts) denoted by the address C-S in the context of VPN-A. For
example, if a particular C-source in VPN-A has address C-S, then
Host(C-S,A) refers to that C-source.
o "SAFI n" route: a BGP route whose Address Family Identifier (AFI)
is either 1 (IPv4) or 2 (IPv6) and whose Subsequent Address Family
Identifier (SAFI) is "n".
o PTA: PMSI Tunnel Attribute [RFC 6514].
Rekhter, et al. Standards Track PAGE 5
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Note that a given extranet C-source is not necessarily allowed to
transmit to every extranet C-receiver; policy determines which
extranet C-sources are allowed to transmit to which extranet
C-receivers. However, in the case of an extranet (ASM) C-group, all
transmitters to the group are allowed to transmit to all the
receivers of the group, and all the receivers of the group are
allowed to receive from all transmitters to the group.
We say that a given VRF "contains" or "has" a multicast C-source (or
that the C-source is "in" the VRF) if that C-source is in a site
connected to that VRF and the VRF originates a UMH-eligible route
(see Section 4) that matches the address of the C-source.
We say that a given VRF "contains" or "has" a multicast C-receiver
(or that the C-receiver is "in" the VRF) if that C-receiver is in a
site connected to that VRF.
We say that a given VRF "contains" or "has" the C-RP for a given ASM
group (or that the C-RP is "in" the VRF) if that C-RP is in a site
connected to that VRF and the VRF originates a unicast route and a
(possibly different, possibly the same) UMH-eligible route (see
Section 4) whose respective address prefixes match the C-RP address.
[RFC 6513] allows a set of "P-tunnels" (defined in Section 3.2 of
[RFC 6513]) to be aggregated together and transported via an outer
P-tunnel; i.e., it allows for the use of hierarchical Label Switched
Paths (LSPs) as P-tunnels. A two-level hierarchical LSP, for
example, can be thought of as a set of "inner tunnels" aggregated
into an outer tunnel. In this document, when we speak of a P-tunnel,
we are always speaking of the innermost P-tunnel, i.e., of a P-tunnel
at the lowest hierarchical level. P-tunnels are identified in the
PMSI Tunnel attributes ("PTAs" in this document) [RFC 6514] of BGP
auto-discovery (A-D) routes. Two PTAs that have the same Tunnel Type
and Tunnel Identifier fields but different MPLS label fields are thus
considered to identify two different P-tunnels. (That is, for the
purposes of this document, the MPLS label included in the PTA, if
any, is considered to be part of the tunnel identifier.)
We say that the NLRI of a BGP S-PMSI A-D route or Source Active A-D
route contains (C-S,C-G) if its Multicast Source field contains C-S
and its Multicast Group field contains C-G. If either or both of
these fields are encoded as a wildcard, we will say that the NLRI
contains (C-*,C-*) (both fields encoded as wildcards), (C-*,C-G)
(Multicast Source field encoded as a wildcard), or (C-S,C-*)
(Multicast Group field encoded as a wildcard).
Rekhter, et al. Standards Track PAGE 6
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
We use the term "VPN security violation" to refer to any situation in
which a packet is delivered to a particular VPN, even though, by
policy, it should not be delivered to that VPN.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC 2119].
1.2. Scope
1.2.1. Customer Multicast Control Protocols
This document presumes that the VPN customer is using PIM - Sparse
Mode (PIM-SM) [RFC 7761] as the multicast control protocol at the
customer sites. PIM-SM may be used in either the ASM service model
or the SSM service model; this document covers both cases. Support
for other customer IP multicast control protocols (e.g., [RFC 5015],
PIM - Dense Mode) is outside the scope of this document. Support for
the use of MPLS multicast control protocols (e.g., [RFC 6388]
[RFC 4875]) by customer sites is also outside the scope of this
document.
When a VPN customer uses ASM, the customer routers need to be able to
map from a C-group address to a C-RP address. These mappings can be
provisioned in each router, or they can be discovered dynamically
through protocols such as the Bootstrap Router (BSR) mechanism
[RFC 5059]. However, it cannot be assumed that such protocols will
automatically work in the context of an extranet. Discussion of the
use of such protocols in an extranet is outside the scope of this
document.
1.2.2. Provider Multicast Control Protocols
[RFC 6513] allows either PIM or BGP to be used as the protocol for
distributing customer multicast routing information. Except where
otherwise specified, such as in Sections 6 and 7, the procedures of
this document cover both cases.
Rekhter, et al. Standards Track PAGE 7
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
1.3. Clarification on Use of Route Distinguishers
[RFC 4364] requires that every VRF be associated with one or more
Route Distinguishers (RDs). Each VPN-IPv4 or VPN-IPv6 route that is
exported from a particular VRF contains, in its NLRI, an RD that is
associated with that VRF.
[RFC 4364] allows a given RD to be associated with more than one VRF,
as long as all the VRFs associated with that RD belong to the same
VPN. However, in the most common deployment model, each RD is
associated with one and only one VRF. [RFC 6513] and [RFC 6514]
presuppose this deployment model. That is, [RFC 6513] and [RFC 6514]
presuppose that every RD is associated with one and only one VRF. We
will call this the "unique VRF per RD" condition.
[RFC 6514] defines the MCAST-VPN address family, which has a number of
route types. Each Intra-Autonomous System (Intra-AS) "Inclusive
Provider Multicast Service Interface" (I-PMSI) A-D route, S-PMSI A-D
route, and Source Active A-D route, when exported from a given VRF,
contains, in its NLRI, an RD that is associated with the VRF.
[RFC 6513] and [RFC 6514] also discuss a class of routes known as
"UMH-eligible" routes; when a UMH-eligible route is exported from a
given VRF, its NLRI contains an RD of the VRF.
[RFC 6514] also defines MCAST-VPN routes whose NLRIs do not contain an
RD of the VRF from which they are exported: the C-multicast Join
routes and the Leaf A-D routes.
Those route types that, when exported from a given VRF, contain (in
their NLRIs) an RD of the VRF, will be known in this document as
"local-RD routes".
Given the "unique VRF per RD" condition, if one sees that two
local-RD routes have the same RD, one can infer that the two routes
originated from the same VRF. This inference can be drawn even if
the two routes do not have the same SAFI, as long as the two routes
are both local-RD routes.
This document builds upon [RFC 6513] and [RFC 6514]; therefore, the
"unique VRF per RD" condition is REQUIRED.
[RFC 6514] presupposes a further requirement on the use of RDs in the
local-RD routes exported from a given VRF. Suppose that a given VRF
exports a Source Active A-D route containing (C-S,C-G). That VRF
will also export a UMH-eligible route matching C-S. [RFC 6514]
presupposes that the UMH-eligible route and the Source Active A-D
route have the same RD.
Rekhter, et al. Standards Track PAGE 8
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
In most cases, not only is a given RD associated with only a single
VRF, but a given VRF is associated with only a single RD. We will
call this the "unique RD per VRF" condition. When this condition
holds, all the local-RD routes exported from a given VRF will have
the same RD. This ensures that the presupposition of the previous
paragraph will hold, i.e., that the RD in a Source Active A-D route
exported from a given VRF will have the same RD as the corresponding
UMH-eligible route exported from the same VRF.
Section 7.3 of this document describes a procedure known as "extranet
separation". When extranet separation is NOT being used, it is
REQUIRED by this document that the "unique RD per VRF" condition
hold. This ensures that all the local-RD routes exported from a
given VRF will have the same RD.
When extranet separation is used, a VRF that contains both extranet
sources and non-extranet sources MUST be configured with two RDs.
One of these RDs is known as the "default RD", and the other is known
as the "extranet RD". It MUST be known by configuration which RD is
the default RD and which is the extranet RD.
When a VRF is configured with only one RD, we will refer to that RD
as the "default RD".
In general, local-RD routes exported from a given VRF will contain
the default RD. However, when extranet separation is used, some of
the local-RD routes exported from the VRF will contain the
extranet RD. Details concerning the exported routes that contain
the extranet RD can be found in Sections 4.1 and 7.3.
Note that the "unique VRF per RD" condition applies to the
extranet RD as well as the default RD. That is, a given extranet RD
is associated with a unique VRF.
1.4. Overview
Consider two VPNs, VPN-S and VPN-R, each of which supports MVPN
functionality as specified in [RFC 6513] and/or [RFC 6514]. In the
simplest configuration, VPN-S is a collection of VRFs, each of which
is configured with a particular Route Target (RT) value (call it
"RT-S") as its import RT and as its export RT. Similarly, VPN-R is a
collection of VRFs, each of which is configured with a particular RT
value (call it "RT-R") as its import RT and as its export RT.
Rekhter, et al. Standards Track PAGE 9
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
In this configuration, multicast C-receivers contained in a VPN-R VRF
cannot receive multicast data traffic from multicast C-sources
contained in a VPN-S VRF. If it is desired to allow this, one needs
to create an MVPN "extranet". Creating an extranet requires
procedures in addition to those specified in [RFC 6513], [RFC 6514],
and [RFC 6625]; this document specifies these additional procedures.
In the example above, the additional procedures will allow a selected
set of routes exported from the VPN-S VRFs (i.e., from the VRFs
containing extranet C-sources) to be imported into the VPN-R VRFs
(i.e., into the VRFs containing extranet C-receivers). These routes
include the routes that are to be eligible for use as UMH routes (see
Section 5.1 of [RFC 6513]) in the extranet, as well as a selected set
of BGP A-D routes (Intra-AS I-PMSI A-D routes, S-PMSI A-D routes, and
Source Active A-D routes). Importing these routes into the VPN-R
VRFs makes it possible to determine, in the context of a VPN-R VRF,
that a particular C-multicast Join needs to be delivered to a
particular VPN-S VRF. It also makes it possible to determine, in the
context of a VPN-R VRF, the P-tunnel through which the aforementioned
VPN-S VRF sends a particular C-flow.
Depending on the type of P-tunnel used, it may also be necessary for
Leaf A-D routes to be exported by one or more VPN-R VRFs and imported
into a VPN-S VRF.
There are no extranet-specific procedures governing the use and
distribution of BGP C-multicast routes.
If PIM is used as the PE-PE protocol for distributing C-multicast
routing information, additional BGP A-D routes must be exported from
the VPN-R VRFs and imported into the VPN-S VRFs, so that the VPN-S
VRFs can join the P-tunnels that the VPN-R VRFs use for sending PIM
control messages. Details can be found in Section 6.
The simple example above describes an extranet created from two
MVPNs, one of which contains extranet C-sources and one of which
contains extranet C-receivers. However, the procedures described in
this document allow for much more complicated scenarios.
For instance, an extranet may contain extranet C-sources and/or
extranet C-receivers from an arbitrary number of VPNs, not just from
two VPNs. An extranet C-receiver in VPN-R may be allowed to receive
multicast traffic from extranet C-sources in VPN-A, VPN-B, and VPN-C.
Similarly, extranet C-sources in VPN-S may be allowed to send
multicast traffic to multicast C-receivers that are in VPN-A, VPN-B,
VPN-C, etc.
Rekhter, et al. Standards Track PAGE 10
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
A given VPN customer may desire that only some of its multicast
C-sources be treated as extranet C-sources. This can be accomplished
by appropriate provisioning of the import and export RTs of that
customer's VRFs (as well as the VRFs of other VPNs that contain
extranet C-receivers for extranet C-flows of the given customer).
A given VPN customer may desire that some of its extranet C-sources
can transmit only to a certain set of VPNs while other of its
extranet C-sources can transmit only to a different set of VPNs.
This can be accomplished by provisioning the VRFs to export different
routes with different RTs.
In all these cases, the VPN customers set the policies, and the
Service Provider (SP) implements the policies by the way it
provisions the import and export RTs of the VRFs. It is assumed that
the customer communicates to the SP the set of extranet C-source
addresses and the set of VPNs to which each C-source can transmit.
(Recall that every C-source that can transmit to an extranet C-group
is an extranet C-source and must be able to transmit to any VPN that
has receivers for that group. This must be taken into account when
the provisioning is done.) This customer/SP communication is part of
the service provisioning process and is outside the scope of this
document.
It is possible that an extranet C-source will transmit both extranet
C-flows and non-extranet C-flows. However, if extranet C-receiver
C-R can receive extranet C-flows from extranet C-source C-S, the
procedures of this document do not prevent C-R from requesting and
receiving the non-extranet flows that are transmitted by C-S.
Therefore, allowing an extranet C-source to transmit non-extranet
C-flows is NOT RECOMMENDED. However, the SP has no control over the
set of C-flows transmitted by a given C-source and can do no more
than communicate this recommendation to its customers.
(Alternatively, the customer and SP may coordinate on setting up
filters to prevent unauthorized flows from being sent to a customer
site; such a procedure is outside the scope of this document.) See
Section 10 ("Security Considerations") for additional discussion of
this issue.
Whenever a VPN is provisioned, there is a risk that errors in
provisioning may result in an unintended cross-connection of VPNs.
This would create a security problem for the customers. When
provisioning an extranet, attention to detail is particularly
important, as an extranet intentionally cross-connects VPNs. Care
must always be taken to ensure that the cross-connections are
according to the policy agreed upon by the SP and its customers.
Rekhter, et al. Standards Track PAGE 11
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Additionally, if one is connecting two VPNs that have overlapping
address spaces, one has to be sure that the inter-VPN traffic neither
originates from nor is destined to the part of the address space that
is in the overlap. Other problems that can arise due to overlapping
address spaces are discussed in Section 2.
2. Extranets and Overlapping Address Spaces
As specified in [RFC 4364], the address space of one VPN may overlap
with the address space of another. A given address may be
"ambiguous" in that it denotes one system within VPN-A and a
different system within VPN-B. In the notation of Section 1.1,
if an address C-S is ambiguous between VPN-A and VPN-B, then
Host(C-S,A) != Host(C-S,B). However, any given address C-S MUST be
unambiguous (i.e., MUST denote a single system) in the context of a
given VPN.
When a set of VRFs belonging to different VPNs are combined into an
extranet, it is no longer sufficient for an address to be unambiguous
only within the context of a single VPN:
1. Suppose that C-S is the address of a given extranet C-source
contained in VPN-A. Now consider the set of VPNs
{VPN-B, VPN-C, ...} containing extranet C-receivers that are
allowed by policy to receive extranet C-flows from VPN-A's C-S.
The address C-S MUST be unambiguous among this entire set of VPNs
{VPN-A, VPN-B, VPN-C, ...}; i.e., Host(C-S,A) == Host(C-S,B) ==
Host(C-S,C).
The implication is that C-S in VPN-A is not necessarily an
extranet C-source for all VPNs that contain extranet C-receivers;
policy MUST be used to ensure that C-S is an extranet C-source
for a given VPN, say VPN-B, only if C-S is unambiguous between
VPN-A and VPN-B.
2. If a given VRF contains extranet C-receivers for a given extranet
C-source, then the address of this C-source MUST be unambiguous
among all the extranet C-sources for which there are C-receivers
in the VRF. This is true whether or not C-sources are in VRFs
that belong to the same VPN or different VPNs.
The implication is that if C-S in VRF-X is ambiguous with C-S in
VRF-Y, then there MUST NOT be any VRF, say VRF-Z, containing
C-receivers that are allowed by policy to receive extranet
C-flows from both C-S in VRF-X and C-S in VRF-Y.
Rekhter, et al. Standards Track PAGE 12
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Note: A VPN customer may be using anycast addresses. An anycast
address is intentionally ambiguous, as it denotes a set of systems
rather than a single system. In this document, we will consider an
anycast address to be unambiguous in a given context as long as it
denotes the same set of systems whenever it occurs in that context.
A multicast C-group address, say C-G, may also be ambiguous in that
it may be used for one multicast group in VPN-A and for an entirely
different multicast group in VPN-B. If a set of MVPNs are combined
into an extranet and C-G is an extranet C-group, it is necessary to
ensure that C-G is unambiguous among the entire set of VPNs whose
VRFs contain extranet C-sources, C-RPs, and/or extranet C-receivers
for that C-group. This may require, as part of the provisioning
process, customer/SP communication that is outside the scope of this
document.
Subject to these restrictions, the SP has complete control over the
distribution of routes in an MVPN. This control is exerted by
provisioning either (1) the export RTs on the VRFs that originate the
routes (i.e., the VRFs that contain the extranet C-sources) or
(2) the import RTs on the VRFs that receive the routes (i.e., the
VRFs that contain the extranet C-receivers), or both.
Some of the rules and restrictions on provisioning the RTs are
applicable to all extranets; these are specified in Section 4.
Sections 6 and 7 list additional rules and restrictions that are
applicable only to particular extranet scenarios.
Even if all the RTs are provisioned according to the above rules and
restrictions, it is still possible for a single P-tunnel to contain
multicast data packets whose source and/or group addresses are
ambiguous in the context of the set of PEs that receive data from the
P-tunnel. That is, the above rules and restrictions are necessary,
but not sufficient, to prevent address ambiguity from causing
misdelivery of traffic. To prevent such misdelivery, additional
procedures or policies must be used.
Sections 2.1 and 2.2 describe scenarios in which a given P-tunnel may
carry data packets with ambiguous addresses. The additional
procedures and policies needed to prevent misdelivery of data in
those scenarios are outlined in Section 2.3. (The detailed
procedures described in Sections 6 and 7 incorporate the
considerations discussed in Section 2.3.)
Rekhter, et al. Standards Track PAGE 13
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
2.1. Ambiguity: P-Tunnel with Extranet/Non-extranet Flows
In the following, we will use the notation "VRF A-n" to mean "VRF n
of VPN-A".
If VPN-A and VPN-B have overlapping address spaces and are part of
the same extranet, then the following problem may exist, as
illustrated in Figure 1.
C-S2(A) C-S1 Join(C-S2(A),G)
\ / /
\ / /
+-------+---+ P1: (C-S1,G), (C-S2(A),G) +---+--------+
|VRF A-1| |---------------------------------| |VRF A-2 |
+-------+PE1| |PE2+--------+
|VRF B-1| |---------------------------------| |VRF B-2 |
+-------+---+ P2: (C-S2(B),G) +---+--------+
/ / \
/ / \
C-S2(B) Join(C-S2(B),G) Join(C-S1,G)
Figure 1: Ambiguity of Extranet and Non-extranet Source Address
Suppose that:
o C-G is an SSM C-group used in VPN-A and VPN-B.
o VRF A-1, on PE1, contains an extranet C-source, with IP address
C-S1, that is allowed to have receivers in VPN-B. VRF A-1 thus
exports to VPN-B a UMH-eligible route matching C-S1.
o In addition, VRF A-1 contains a non-extranet C-source with IP
address C-S2. VRF A-1 exports a UMH-eligible route matching C-S2
to other VPN-A VRFs but NOT to VPN-B.
o VRF B-1, also on PE1, contains a non-extranet C-source with IP
address C-S2. A UMH-eligible route matching C-S2 is thus exported
from VRF B-1 to other VRFs in VPN-B.
o Host(C-S2,A) != Host(C-S2,B). That is, C-S2 is an ambiguous
address in any extranet that contains both VPN-A VRFs and VPN-B
VRFs.
o VRF B-2, on some other PE, say PE2, requests the multicast flow
(C-S1,C-G). In the context of VRF B-2, C-S1 matches the route
exported from VRF A-1. Thus, B-2's request to receive the
(C-S1,C-G) flow is transmitted to VRF A-1.
Rekhter, et al. Standards Track PAGE 14
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
o VRF A-1 responds to VRF B-2's request for (C-S1,C-G) traffic by
transmitting that traffic on P-tunnel P1.
o VRF B-2 joins P-tunnel P1 in order to receive the (C-S1,C-G)
traffic.
o VRF A-2, on PE2, requests the (non-extranet) multicast flow
(C-S2,C-G). In the context of VRF A-2, C-S2 matches the route
exported from VRF A-1. Thus, A-2's request to receive the
(C-S2,C-G) traffic is transmitted to VRF A-1.
o VRF A-1 responds to VRF A-2's request for (C-S2,C-G) traffic by
transmitting that traffic on P-tunnel P1.
o VRF A-2 joins P-tunnel P1 in order to receive the (C-S2,C-G)
traffic.
o VRF B-2 requests the (non-extranet) multicast flow (C-S2,C-G). In
the context of VRF B-2, C-S2 matches the route exported from VRF
B-1. Thus, B-2's request to receive the (C-S2,C-G) flow is
transmitted to VRF B-1.
o VRF B-1 responds to VRF B-2's request for (C-S2,C-G) traffic by
transmitting that traffic on P-tunnel P2.
o VRF B-2 joins P-tunnel P2.
Since VRF B-2 has joined P-tunnel P1 and P-tunnel P2, it will receive
(C-S2,C-G) traffic on both P-tunnels. The (C-S2,C-G) traffic that
VRF B-2 needs to receive is traveling on P-tunnel P2; this (C-S2,C-G)
traffic must be forwarded by B-2 to any attached customer sites that
have C-receivers for it. But B-2 MUST discard the (C-S2,C-G) traffic
that it receives on P1, as this is not the traffic that it has
requested. If the (C-S2,C-G) traffic arriving on P1 were forwarded
to B-2's customer sites, the C-receivers would not be able to
distinguish the two flows, and the result would be a corrupted data
stream.
Note that the procedures of Section 9.1.1 of [RFC 6513] ("Discarding
Packets from Wrong PE") will not cause VRF B-2 to discard the
(C-S2,C-G) traffic that arrives on tunnel P1, because P1 and P2 have
the same upstream PE.
Therefore, it is necessary to EITHER (1) prevent the above scenario
from occurring OR (2) ensure that multicast data packets will be
discarded if they arrive on the wrong P-tunnel (even if they arrive
from the expected PE). See Section 2.3 for further discussion of
this issue.
Rekhter, et al. Standards Track PAGE 15
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
2.2. Ambiguity: P-Tunnel with Multiple Extranet Flows
Figure 2 illustrates another example of how overlapping address
spaces may cause a problem.
C-S2(A2D) C-S1(A2C) Join(C-S2(A2D),G)
\ / /
\ / /
+-------+---+ P1: (C-S1(A2C),G), (C-S2(A2D),G)+---+--------+
|VRF A-1| |---------------------------------| |VRF D-1 |
+-------+PE1| |PE2+--------+
|VRF B-1| |---------------------------------| |VRF C-1 |
+-------+---+ P2: (C-S2(B2C),G) +---+--------+
/ / \
/ / \
C-S2(B2C) / \
Join Join
(C-S2(B2C),G) (C-S1(A2C),G)
Figure 2: Ambiguity of Extranet Source Addresses
Suppose that:
o C-G is an SSM C-group address that is used in VPN-A, VPN-B, VPN-C,
and VPN-D.
o VRF A-1, on PE1, contains an extranet C-source, with IP address
C-S1, that is allowed by policy to have C-receivers in VPN-C (but
not in VPN-D). VRF A-1 thus exports a UMH-eligible route matching
C-S1 to VPN-C.
o In addition, VRF A-1 contains an extranet C-source, with IP
address C-S2, that is allowed by policy to have C-receivers in
VPN-D (but not in VPN-C). VRF A-1 thus exports a UMH-eligible
route matching C-S2 to VPN-D.
o VRF B-1, also on PE1, contains an extranet C-source, with IP
address C-S2, that is allowed by policy to have C-receivers in
VPN-C (but not in VPN-D). VRF B-1 thus exports a UMH-eligible
route matching C-S2 to VPN-C.
o Host(C-S2,A) != Host(C-S2,B). That is, C-S2 is an ambiguous
address in any extranet that contains both VPN-A VRFs and
VPN-B VRFs.
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
o VRF C-1, on some other PE, say PE2, requests the extranet
multicast flow (C-S1,C-G). In the context of VRF C-1, C-S1
matches the route exported from VRF A-1. Thus, C-1's request to
receive the (C-S1,C-G) flow is transmitted to VRF A-1.
o VRF A-1 responds to VRF C-1's request for (C-S1,C-G) traffic by
transmitting that traffic on P-tunnel P1.
o VRF C-1 joins P-tunnel P1 in order to receive the (C-S1,C-G)
traffic.
o VRF C-1 requests the extranet multicast flow (C-S2,C-G). In the
context of VRF C-1, C-S2 matches the route exported from VRF B-1.
Thus, C-1's request to receive the (C-S2,C-G) flow is transmitted
to VRF B-1.
o VRF B-1 responds by transmitting its (C-S2,C-G) traffic on
P-tunnel P2.
o VRF C-1 joins P-tunnel P2 in order to receive the (C-S2,C-G)
traffic.
o VRF D-1, on PE2, requests the extranet multicast flow (C-S2,C-G).
In the context of VRF D-1, C-S2 matches the route exported from
VRF A-1. Thus, D-1's request to receive the (C-S2,C-G) flow is
transmitted to VRF A-1.
o VRF A-1 responds by transmitting its (C-S2,C-G) traffic on
P-tunnel P1.
o VRF D-1 joins P-tunnel P1 in order to receive the (C-S2,C-G)
traffic.
In this example, VRF A-1 has chosen to use the same P-tunnel, P1, to
carry both its (C-S2,C-G) traffic and the (C-S1,C-G) traffic. VRF
C-1 has joined tunnel P1 in order to receive the (C-S1,C-G) traffic
from VRF A-1, which means that VRF C-1 will also receive the unwanted
(C-S2,C-G) traffic from P1. VRF C-1 is also expecting (C-S2,C-G)
traffic from VRF B-1; this traffic will be received from P2. Thus,
VRF C-1 is receiving (C-S2,C-G) traffic on both tunnels, and both
C-flows arrive from the expected PE, PE1.
Therefore, it is necessary to EITHER (1) prevent the above scenario
from occurring OR (2) ensure that VRF C-1 discards any (C-S,C-G)
traffic that arrives from the wrong P-tunnel. See Section 2.3 for
further discussion of this issue.
Rekhter, et al. Standards Track PAGE 17
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Note that the ambiguity described in this section (Section 2.2) would
not occur if C-G were an (ASM) extranet C-group. In that case, the
scenario would violate the rule, given previously in Section 2,
requiring that all sources sending to a particular ASM extranet
C-group must have addresses that are unambiguous over all the MVPNs
receiving traffic for that C-group.
2.3. Preventing Misdelivery in These Scenarios
There are two ways to prevent the scenarios discussed in Sections 2.1
and 2.2 from resulting in misdelivery of data; these techniques are
discussed in Sections 2.3.1 and 2.3.2, respectively.
2.3.1. Do Not Deliver Packets from the Wrong P-tunnel
Consider a particular C-flow that has receivers in a particular VRF.
Sections 6 and 7 describe a set of procedures that enable an egress
PE to determine the "expected P-tunnel" for that C-flow in the
context of that VRF. If a PE receives packets of the C-flow (as
determined by the IP source and/or destination address of the
packet), it checks to see if the packet was received on the expected
P-tunnel for that VRF. If so, the packet is delivered to the VRF
(and thus to the C-flow's receivers in that VRF). If not, the packet
is not delivered to the VRF.
Note that at a given egress PE, the wrong P-tunnel for one VRF may be
the correct P-tunnel for another.
These procedures, if applied at every PE that joins a given P-tunnel,
are sufficient to prevent misdelivery of traffic in the scenarios
discussed in Sections 2.1 and 2.2.
IF these procedures cannot be applied by every PE that is attached to
a given extranet, then the policies of Section 2.3.2 MUST be applied
at every VRF containing C-sources for that extranet.
In some cases, however, it may be safe to deliver packets that arrive
from other than the expected P-tunnel. Suppose that it is known that
every packet gets transmitted on only a single P-tunnel. (This will
be the case if the "single PMSI per C-flow" transmission model,
discussed in Section 3.1, is being used.) Suppose also that it is
known that T1 and T2 carry only packets that arrived at the same
ingress PE, over one or more VRF interfaces that are associated with
the same VRF (i.e., that there is a particular VRF that is the
ingress VRF for ALL the packets carried by T1 or T2). In this case,
if T1 is the expected P-tunnel for a given (C-S,C-G), it is NOT
necessary to discard (S,G) packets that arrive over T2.
Rekhter, et al. Standards Track PAGE 18
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
It is not always possible to determine whether two P-tunnels are
carrying packets from the same ingress VRF. However, in some cases,
this can be determined by examination of the A-D routes in which the
tunnels have been advertised.
Consider the following example:
o Tunnel T1 is a Point-to-Multipoint (P2MP) multipoint Label
Distribution Protocol (mLDP) or RSVP-TE P-tunnel advertised in an
Intra-AS I-PMSI A-D route (call it "R1").
o Tunnel T2 is a P2MP mLDP or RSVP-TE P-tunnel advertised in an
S-PMSI A-D route (call it "R2").
o The respective NLRIs of R1 and R2 contain the same RD value.
o The MPLS Label field of R1's PTA is zero, and the MPLS label value
of R2's PTA is zero.
In this example, it can be concluded that T1 and T2 are carrying
packets from the same ingress VRF. Thus, if T1 is the expected
P-tunnel for a (C-S,C-G) flow, (S,G) packets from T2 can be safely
delivered to the egress VRF; they do not need to be discarded.
Similarly, if T2 is the expected P-tunnel for a (C-S,C-G) flow, (S,G)
packets from T1 can be safely delivered to the egress VRF.
Another example is the following:
o Tunnel T3 is a P2MP mLDP or RSVP-TE P-tunnel advertised in a
(C-*,C-*) S-PMSI A-D route (call it "R3").
o Tunnel T4 is a P2MP mLDP or RSVP-TE P-tunnel advertised in a
(C-S,C-G) S-PMSI A-D route (call it "R4").
o The respective NLRIs of R3 and R4 contain the same RD value.
o The MPLS Label field of R3's PTA is zero, and the MPLS label value
of R4's PTA is zero.
In this example, it can be concluded that T3 and T4 are carrying
packets from the same ingress VRF. Thus, if T3 is the expected
P-tunnel for a (C-S,C-G) flow, (S,G) packets from T4 can be safely
delivered to the egress VRF; they do not need to be discarded.
Similarly, if T4 is the expected P-tunnel for a (C-S,C-G) flow,
(S,G) packets from T3 can be safely delivered to the egress VRF.
Rekhter, et al. Standards Track PAGE 19
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
When Ingress Replication (IR) P-tunnels are being used, please see
[MVPN-IR], especially Section 7 ("The PTA's 'MPLS Label' Field") for
a discussion of how to determine when packets from other than the
expected P-tunnel must be discarded.
2.3.2. Policies to Prevent Ambiguity on a P-Tunnel
For P-tunnels that are advertised in S-PMSI A-D routes whose NLRI
contains (C-S,C-G) or (C-S,C-*), the ambiguities described in
Sections 2.1 and 2.2 can be prevented by provisioning a policy that
assigns, to such P-tunnels, only flows from the same C-source.
However, it is not always possible to determine, through inspection
of the control messages, whether this policy has been deployed. For
instance, suppose that (1) a given VRF has imported a set of S-PMSI
A-D routes, (2) each route in the set has bound only a single
(C-S1,C-G1) to a single P-tunnel, and (3) each route in the set
identifies a different P-tunnel in its PTA than the P-tunnel
identified by the PTA of any other route in the set. One cannot
infer from this that there is no ambiguity, as the same P-tunnel may
also have been advertised in an S-PMSI A-D route that is not imported
by the given VRF, and that S-PMSI A-D route may have bound
(C-S2,C-G2) to the P-tunnel, where C-S1 != C-S2.
Therefore, in order to determine that a given P-tunnel (advertised in
a (C-S,C-G) or (C-S,C-*) S-PMSI A-D route) carries only C-flows from
a single C-source, a PE must have a priori knowledge (through
provisioning) that this policy has been deployed. In the remainder
of this document, we will refer to this policy as the "single
C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" policy. Note that this
policy is only applicable to P-tunnels that are advertised only in
(C-S,C-G) or (C-S,C-*) S-PMSI A-D routes.
Of course, if a P-tunnel is advertised in (a) an I-PMSI A-D route,
(b) an S-PMSI A-D route whose NLRI contains (C-*,C-*), or (c) an
S-PMSI A-D route whose NLRI contains (C-*,C-G), then it is always
possible for the P-tunnel to contain traffic from multiple C-sources;
there is no policy that can prevent that.
However, if a P-tunnel advertised in a (C-*,C-G) S-PMSI A-D route
contains only traffic addressed to a single C-G, the address
uniqueness rules of Section 2 prevent the C-source addresses from
being ambiguous; the set of C-sources transmitting to a particular
extranet C-group address must be unambiguous over the set of MVPNs
that have receivers for that C-group. So, for P-tunnels that are
advertised in (C-*,C-G) S-PMSI A-D routes, the ambiguities described
in Sections 2.1 and 2.2 can be prevented by provisioning a policy
Rekhter, et al. Standards Track PAGE 20
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
that assigns to such P-tunnels only flows to the same extranet
C-group. We will refer to this policy as the "single C-group per
(C-*,C-G) P-tunnel" policy.
These considerations can be summarized as follows. IF the procedures
referenced in Section 2.3.1 cannot be applied, then the PEs MUST be
provisioned so that all of the following conditions hold true for the
VRFs that contain extranet C-sources:
o the "single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" policy
is provisioned,
o either no (C-*,C-G) S-PMSI A-D routes are advertised or the
"single C-group per (C-*,C-G) P-tunnel" policy is provisioned,
o no P-tunnels are advertised in I-PMSI A-D routes, and
o no (C-*,C-*) S-PMSI A-D routes are advertised.
Section 3 of this document describes a procedure known as "extranet
separation". When extranet separation is used, the ambiguity
described in Section 2.1 is prevented. However, the ambiguity
described in Section 2.2 is not prevented by extranet separation.
Therefore, the use of extranet separation is not a sufficient
condition for avoiding the use of the procedures discussed in
Section 2.3.1. Extranet separation is, however, implied by the
policies discussed in this section (Section 2.3.2).
3. Extranet Transmission Models
This document specifies several "extranet transmission" models. A
given VRF containing extranet C-sources or C-receivers MUST use only
one of these models. Further, if VRF-S contains extranet C-sources,
VRF-R contains extranet C-receivers, and it is allowed by policy for
an extranet C-receiver in VRF-R to receive a C-flow from an extranet
C-source in VRF-S, then VRF-S and VRF-R MUST use the same extranet
transmission model. The model used by a given VRF is determined by
provisioning.
3.1. Transmitting an Extranet C-Flow on a Single PMSI
In one extranet transmission model, which we call the "transmitting
an extranet C-flow on a single PMSI" model or, more simply, the
"single PMSI per C-flow" model, a PE transmitting a packet of an
extranet C-flow transmits it on only a single PMSI. If the PMSI is
instantiated by a multicast P-tunnel, this means that the PE
transmits the packet on a single P-tunnel. Of course, if the PE is a
replication point for that multicast P-tunnel, the packet is
Rekhter, et al. Standards Track PAGE 21
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
transmitted more than once by the PE. Similarly, if the PMSI is
instantiated by IR, each packet may be transmitted multiple times.
It is still the case, though, that the packet is transmitted only on
one PMSI.
This document provides procedures for supporting this transmission
model using either BGP or PIM as the PE-PE C-multicast control
protocol.
There are two variants of this transmission model: "without extranet
separation" and "with extranet separation".
3.1.1. Without Extranet Separation
In this variant, multicast data traffic from extranet C-sources and
from non-extranet C-sources may be carried in the same P-tunnel.
This document provides procedures for supporting this variant using
either BGP or PIM as the PE-PE C-multicast control protocol.
3.1.2. With Extranet Separation
In this variant, multicast data traffic from extranet C-sources and
from non-extranet C-sources are never carried in the same P-tunnel.
Under certain circumstances, this can reduce the amount of multicast
data traffic that is delivered unnecessarily to certain PE routers.
It also eliminates the ambiguity discussed in Section 2.1.
By definition, when extranet separation is used, the following rule
MUST be applied:
Traffic from extranet C-sources MUST NOT be carried in the same
P-tunnel as traffic from non-extranet C-sources.
This rule does not impact those VRFs that contain only non-extranet
C-sources, nor does it impact those VRFs that contain only extranet
C-sources. However, if a particular VRF contains both kinds of
C-sources, it will need to advertise some P-tunnels that are used for
carrying only extranet C-flows and some that are used only for
carrying non-extranet C-flows.
This document provides procedures for supporting extranet separation
when BGP is used as the PE-PE C-multicast control protocol. Support
for extranet separation using PIM as the PE-PE C-multicast control
protocol is outside the scope of this document.
Rekhter, et al. Standards Track PAGE 22
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
3.2. Transmitting an Extranet C-Flow over Multiple PMSIs
The second extranet transmission model is called the "transmitting an
extranet C-flow over multiple PMSIs" model or, more simply, the
"multiple PMSIs per C-flow" model. In this model, a PE may transmit
the packets of an extranet C-flow on several different PMSIs.
Support for extranet separation with this model is outside the scope
of this document.
This document provides procedures for supporting this transmission
model when PIM is used as the PE-PE C-multicast control protocol.
Support for this transmission model when BGP is used as the PE-PE
C-multicast control protocol is outside the scope of this document.
4. Distribution of Routes That Match C-S/C-RP Addresses
4.1. UMH-Eligible Routes
As described in Section 5.1 of [RFC 6513], in order for a C-flow
(C-S,C-G) to be carried across the SP backbone, a VRF that has
multicast receivers for that C-flow must import a route that matches
C-S, and this route must be "eligible for UMH selection". In this
document, we will refer to these routes as "UMH-eligible extranet
C-source routes".
The UMH-eligible extranet C-source routes do not necessarily have to
be unicast routes; they MAY be SAFI 129 routes (see Section 5.1.1 of
[RFC 6513]). For example, suppose that one wants a VPN-R C-receiver
to be able to receive extranet C-flows from C-sources in VPN-S but
does not want any VPN-R system to be able to send unicast traffic to
those C-sources. One can achieve this by using SAFI 129 routes as
the UMH-eligible routes exported from VPN-S and imported by VPN-R.
Since SAFI 129 routes are used only for UMH determination and not for
unicast routing, this allows the multicast traffic to be forwarded
properly but does not create unicast routes to the C-sources.
If a customer is using PIM-SM in the ASM model and one or more
customer sites have C-receivers that are allowed by policy to join a
(C-*,C-G) tree, where C-G is an extranet C-group, then any VRF with
C-receivers for that group MUST import a UMH-eligible route that
matches C-RP, where C-RP is the Rendezvous Point (RP) address
for C-G.
The UMH-eligible extranet C-source and C-RP routes do not have to be
"host routes". That is, they can be routes whose IPv4 address
prefixes are not 32 bits in length or whose IPv6 address prefixes are
not 128 bits in length. So, it is possible for a UMH-eligible
Rekhter, et al. Standards Track PAGE 23
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
extranet C-source route to match the address of an extranet C-source
and to also match the address of a non-extranet C-source. However,
if such a route is exported from a VPN-S VRF and imported by a VPN-R
VRF, VPN-R receivers will be able to receive C-flows from any
non-extranet C-sources whose addresses match that route. To prevent
this, the VPN-S VRF SHOULD be provisioned such that it will NOT
export a UMH-eligible route that matches (in the context of the VPN-R
VRF) both extranet C-sources and non-extranet C-sources. Failure to
follow this rule may result in a VPN security violation. (See
Section 10.)
In general, one does not want ALL the routes from the VPN-S VRFs to
be exported to all the VPN-R VRFs, as only a subset of the routes in
the VPN-S VRFs will be UMH-eligible extranet C-source routes. Route
distribution is, as is always the case for a BGP/MPLS IP VPN
[RFC 4364], controlled by Route Targets (RTs). A variety of route
distribution policies can be created by appropriately provisioning
the import and export RTs of the various VRFs.
For example, the VPN-S VRFs that contain extranet C-sources could be
configured to apply an export RT whose value is "RT-A-extranet" to
the routes that match the extranet C-sources. The VPN-R VRFs that
contain extranet C-receivers allowed to receive extranet C-flows
from VPN-S extranet C-sources could then be configured with
"RT-A-extranet" as an import RT.
Arbitrarily complex policies can be created by suitable manipulation
of the import and export RTs.
4.1.1. Extranet Separation
If extranet separation is being used and a given VRF is exporting
UMH-eligible routes for both extranet C-sources and non-extranet
C-sources, then the VRF MUST be configured not only with its
default RD but also with an extranet RD. The exported UMH-eligible
routes MUST contain the extranet RD in their NLRIs.
Rekhter, et al. Standards Track PAGE 24
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
4.2. Distribution of Unicast Routes Matching C-RPs and DRs
Consider a C-source, C-S, that may transmit to a particular extranet
C-group, C-G.
In order to follow the procedures of [RFC 7761],
o The "first-hop designated router (DR)" for C-S needs to be able to
unicast PIM Register messages to a C-RP that services C-G.
o The C-RPs servicing C-G need to be able to unicast PIM
Register-Stop messages to the DR for C-S.
It follows that if a VRF contains C-S but does not contain a C-RP for
C-G, then the VRF MUST import a unicast route matching a C-RP for
C-G. Note that the unicast route matching the C-RP is needed whether
or not the VRF has also imported a SAFI 129 route matching the C-RP.
(If the VRF also contains receivers for C-G and UMH determination is
being done using SAFI 129 routes, both a unicast route and a SAFI 129
matching C-RP route are needed.)
Similarly, if a VRF contains a C-RP for C-G but does not contain C-S,
the VRF MUST import a unicast route matching the DR for C-S. Note
that the unicast route matching the DR for C-S is needed even if UMH
determination is being done using SAFI 129 routes; in that case, if
the VRF also contains receivers for C-G, it needs to import a
SAFI 129 route matching C-S and a unicast route matching the DR
for C-S.
If, for a particular extranet C-group, C-G, the customer is using
"anycast-RP" [RFC 3446] [RFC 4610] or the Multicast Source Discovery
Protocol (MSDP) [RFC 3618], then all the C-RPs serving C-G need to
send unicast messages to each other. Thus, any VRF that contains a
C-RP for C-G needs to import unicast routes matching ALL the other
C-RPs that serve C-G.
The need to distribute these unicast routes is usually not a problem
as long as all the C-sources and C-RPs for C-G are in the same MVPN.
If, however, the C-sources are not all in the same MVPN, great care
must be taken to ensure that the unicast routes mentioned above are
properly distributed.
There may be scenarios in which all the C-sources for C-G are in the
same MVPN, but there are receivers in different VPNs, and some or all
of the VPNs with receivers have their own C-RPs for C-G. In this
case, care must be taken to ensure that the C-RPs can all unicast to
each other.
Rekhter, et al. Standards Track PAGE 25
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
4.3. Route Targets and Ambiguous UMH-Eligible Routes
This section imposes a constraint on the way RTs are assigned to
(a) UMH-eligible routes and (b) the BGP A-D routes that advertise
P-tunnels (i.e., BGP A-D routes that contain a PTA). The constraint
specified here applies to any extranet for which the ambiguity
described in Section 2.2 is possible. (The conditions under which
such ambiguity is possible are also described in Section 2.2.)
We want to ensure that, in any given VRF, the UMH-eligible route
matching a given extranet C-source has an RT in common with every BGP
A-D route that advertises a P-tunnel that may be used to carry
extranet multicast traffic from that C-source. We also want to
ensure that the UMH-eligible route matching a given extranet C-source
does not have any RT in common with any BGP A-D route that advertises
a P-tunnel that may be used to carry any multicast traffic from a
different C-source that has the same IP address. This enables us to
determine whether traffic that appears to be from the given C-source
is really arriving on the wrong P-tunnel and hence is really from a
different C-source with the same IP address.
Suppose that an IP address C-S is used in VPN-A as the address of one
system and used in VPN-B as the address of a different system. In
this case, one or more VPN-A VRFs may export a VPN-IP route whose
NLRI is <RD1,S>, and one or more VPN-B VRFs may export a VPN-IP route
whose NLRI is <RD2,S>, where RD1 != RD2. Consider two routes -- R1
and R2 -- for which the following conditions all hold:
o R1 and R2 are UMH-eligible extranet C-source or C-RP routes, or
are unicast routes matching a C-RP.
o R1 is exported from a VRF of VPN-A, while R2 is exported from a
VRF of a different VPN, say VPN-B.
o R1's NLRI specifies IP address prefix S/n.
o R2's NLRI specifies IP address prefix S/m.
o m >= n (S/m is either the same as or more specific than S/n).
o There is some host address H such that:
* H denotes a different system in VPN-A than in VPN-B, and
* H/m == S/m (so either S/m or S/n might be a longest match for H
in some VRF).
Rekhter, et al. Standards Track PAGE 26
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
We impose the following constraint: RTs MUST be assigned in such a
way that R1 and R2 do not have any RT in common.
(This constraint is not as onerous as it may seem. Typically, R1 and
R2 would not have an RT in common, as that might result in their
being imported into the same VRF, making the address H ambiguous in
that VRF.)
Sections 6 and 7 specify procedures for determining if a received
C-flow has been received over the expected P-tunnel. Those
procedures will not work if this constraint is violated. (The
constraint described in this section is necessary, but not
sufficient, for the procedures of Sections 6 and 7 to work;
additional constraints that cover the assignment of RTs to BGP A-D
routes are given in subsequent sections.)
4.4. Dynamically Marking Extranet Routes
4.4.1. The Extranet Source Extended Community
Sections 4.1, 4.2, and 4.3 place specific requirements on the way in
which certain VPN-IP routes are distributed. In order to ensure that
these requirements are met, a VPN customer must tell its SP which
routes are the matching routes for extranet C-sources and C-RPs.
This may be done as part of the provisioning process. Note that this
does not necessarily require customer/provider interaction every time
the customer adds a new extranet C-source or C-RP, but only when the
IP address of the new C-source or C-RP does not match an existing
route that is already being distributed as a VPN-IP extranet route.
Nevertheless, it seems worthwhile to support an OPTIONAL mechanism
that allows a customer to dynamically mark certain routes as being
extranet routes.
To facilitate this, we define a new Transitive Opaque Extended
Community (see [RFC 4360], [RFC 7153], and Section 9 of this document):
the Extranet Source Extended Community. When a Customer Edge (CE)
router advertises (via BGP) a route to a PE router and the AFI/SAFI
of the route is 1/1, 1/2, 1/4, 2/1, 2/2, or 2/4, the Extranet Source
Extended Community MAY be attached to the route. The value field of
the Extended Community MUST be set to zero. By placing this Extended
Community on a particular route, a CE router indicates to a PE router
that the procedures of Sections 4.1, 4.2, and 4.3 are to be applied
to that route. That is, the CE router may use this Extended
Community to indicate to the PE router that a particular route is to
be treated as a route that matches the address of an extranet source
and is to be exported accordingly to other VPNs. A PE router that
interprets this Extended Community MUST ignore the contents of the
value field.
Rekhter, et al. Standards Track PAGE 27
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Whether a CE router uses the Extranet Source Extended Community is
determined by the configuration of the CE router. If used, the set
of routes to which the Extended Community is attached is also
determined by configuration of the CE. Note that a particular PE
router may or may not support the use of the Extranet Source Extended
Community by a particular CE router; this is determined by the
service agreement between the SP and its customer.
If a CE is advertising SAFI 2 routes to the PE as the UMH-eligible
extranet C-source and C-RP routes and the CE is using the Extranet
Source Extended Community, it is important that the CE attach that
Extended Community to the SAFI 2 routes, rather than just to the
corresponding SAFI 1 routes. Otherwise, extranet receivers may not
be able to join the (C-S,C-G) or (C-*,C-G) multicast trees.
However, if the C-sources and the C-RPs for a given extranet C-group
are not all in the same VPN, the Extended Community would also have
to be attached to the SAFI 1 routes that match the C-RP addresses and
to the SAFI 1 routes that match the addresses of the first-hop
designated routers for all the C-sources. Otherwise, the first-hop
routers might not be able to send PIM Register messages to the C-RPs,
and the C-RPs might not be able to send PIM Register-Stop messages to
the first-hop routers.
While this Extended Community allows a customer to inform the SP
dynamically that certain routes are "extranet routes", it does not
allow a customer to control the set of RTs that the route will carry
when it is redistributed as a VPN-IP route. Thus, it is only useful
when all the extranet routes from a given VRF are exported with
exactly the same set of RTs. (cf. Section 4.3.1 of [RFC 4364], which
does provide a mechanism that, if properly supported by the SP,
allows the customer to determine the set of RTs carried by a VPN-IP
route.) A CE SHOULD NOT attach the Extranet Source Extended
Community to any route for which it uses another method of specifying
the RTs to be carried by that route. A CE SHOULD NOT attach the
Extranet Source Extended Community to a route unless all the extranet
routes from the CE's VPN are intended to carry the same set of RTs.
A PE SHOULD ignore the Extranet Source Extended Community if it
appears on a route that the CE should not have put it on. A PE that
ignores the Extranet Source Extended Community SHOULD NOT follow the
procedures of Section 4.4.2.
Note that misconfiguration on the CE router can result in the
Extranet Source Extended Community being mistakenly attached to a
route that is not intended to be exported as an extranet route. This
could result in a VPN security violation.
Rekhter, et al. Standards Track PAGE 28
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
4.4.2. Distribution of Extranet Source Extended Community
Suppose that a PE receives from a CE a route (call it "R") with the
Extranet Source Extended Community. The PE must determine (via the
considerations discussed in Section 4.4.1) whether it should ignore
that Extended Community on route R; if it should ignore the Extended
Community, the procedures described in this section are not followed.
Otherwise, when the PE originates a VPN-IP route corresponding to
route R, the PE MUST attach this Extended Community to that route.
A Route Reflector MUST NOT add or remove the Extranet Source Extended
Community from the VPN-IP routes reflected by the Route Reflector,
including the case where VPN-IP routes received via Internal BGP
(IBGP) are reflected to External BGP (EBGP) peers (inter-AS
option (c); see Section 10 of [RFC 4364]). The value of the Extended
Community MUST NOT be changed by the Route Reflector.
When re-advertising VPN-IP routes, Autonomous System Border Routers
(ASBRs) MUST NOT add/remove the Extranet Source Extended Community
from these routes. This includes inter-AS options (b) and (c) (see
Section 10 of [RFC 4364]). The value of the Extended Community
MUST NOT be changed by the ASBRs.
When a PE advertises (via BGP) IP routes to a CE, these routes
MUST NOT carry the Extranet Source Extended Community unless the
PE-CE connection is actually an inter-AS option (a) connection (see
Section 10 of [RFC 4364]). When the PE-CE connection is not an
inter-AS option (a) connection, a CE that receives an IP route with
the Extranet Source Extended Community MUST remove it from the route
before re-advertising the route.
The rules for attaching the Extranet Source Extended Community to a
VPN-IP route, and the rules for propagating that Extended Community,
are needed in order to support the scenario in which a VPN contains
an option (a) interconnect (see Section 10 of [RFC 4364]). At the
option (a) interconnect, the VPN-IP route gets translated back to an
IP route, and the RTs are stripped off before the IP route is
propagated. If the Extranet Source Extended Community has also been
stripped off, there is no way for the router at the other end of the
option (a) interconnect to know that the route represents an extranet
source. Thus, the technique of using the Extranet Source Extended
Community to dynamically signal that a particular route represents an
extranet source will not work correctly across an option (a)
interconnect unless the rules in this section are followed.
Rekhter, et al. Standards Track PAGE 29
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
4.5. The Extranet Separation Extended Community
We define a new Transitive Opaque Extended Community: the Extranet
Separation Extended Community (see [RFC 4360], [RFC 7153], and
Section 9 of this document). This Extended Community is used only
when extranet separation is being used. Its value field MUST be set
to zero upon origination, MUST be ignored upon reception, and MUST be
passed unchanged by intermediate routers. A Route Reflector MUST NOT
add or remove the Extranet Separation Extended Community from the
routes it reflects, including the case where routes received via IBGP
are reflected to EBGP peers (inter-AS option (c); see Section 10 of
[RFC 4364]).
If a VRF has been provisioned to use extranet separation and that VRF
has been provisioned to transmit any extranet C-flows on a P-tunnel
that it advertises in an I-PMSI A-D route or a (C-*,C-*) S-PMSI A-D
route, then any UMH-eligible routes that are exported from that VRF
following the procedures of Sections 4.1, 4.2, and 4.3 MUST carry the
Extranet Separation Extended Community. In addition, if an I-PMSI
A-D route and/or (C-*,C-*) S-PMSI A-D route exported from that VRF is
used to carry extranet traffic, that A-D route MUST also carry the
Extranet Separation Extended Community. Further details may be found
in Sections 7.3, 7.4.4, and 7.4.5.
5. Origination and Distribution of BGP A-D Routes
Except where otherwise specified, this section describes procedures
and restrictions that are independent of the PE-PE C-multicast
control protocol.
5.1. Route Targets of UMH-Eligible Routes and A-D Routes
Suppose that there is an extranet C-flow such that:
o The extranet C-source of that C-flow is in VRF A-1.
o One or more extranet C-receivers of that C-flow are in VRF B-1.
In this case, VRF A-1 MUST export a UMH-eligible route that matches
the extranet C-source address, and VRF B-1 MUST import that route.
In addition, VRF A-1 MUST export an Intra-AS I-PMSI A-D route or an
S-PMSI A-D route specifying the P-tunnel through which it will send
the data traffic of the given extranet C-flow, and VRF B-1 MUST
import that route. If BGP is the PE-PE C-multicast control protocol,
then under certain conditions (as specified in [RFC 6514]), VRF A-1
may also need to export a Source Active A-D route specifying that it
contains a source of the given C-flow, and VRF B-1 must import that
Source Active A-D route. That is, in order for VRF B-1 to receive a
Rekhter, et al. Standards Track PAGE 30
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
C-flow from a given extranet C-source contained in VRF A-1, VRF A-1
MUST export a set of A-D routes that are "about" that source, and VRF
B-1 MUST import them.
One way to ensure this is to provision an RT that is carried by all
the routes exported from VRF A-1 that are "about" a given extranet
C-source and also provision this RT as an import RT at any VRF (such
as VRF B-1) that is allowed to receive extranet flows from that
source.
If the "single PMSI per C-flow" transmission model is being used
(with or without extranet separation), there is an additional
requirement, stated below, regarding the way RTs are provisioned, as
the RTs carried by a UMH-eligible route that matches a given extranet
C-source may need to be used to identify the A-D routes that are
"about" that source.
Consider the following scenario:
o IP address S is the address of one system in VPN-A and the address
of a different system in VPN-B.
o VRF A-1 on PE1 exports UMH-eligible route R1, which is a matching
route for S.
o VRF A-1 on PE1 exports an A-D route P1 whose PTA identifies a
P-tunnel through which VRF A-1 may send traffic whose C-source is
S, where one of the following conditions holds:
* P1 is an I-PMSI A-D route, OR
* P1 is an S-PMSI A-D route whose NLRI contains (C-*,C-*) or
(C-*,C-G), OR
* P1 is an S-PMSI A-D route whose NLRI contains (C-S,C-G) or
(C-S,C-*), BUT the "single C-source per (C-S,C-G) or (C-S,C-*)
P-tunnel" policy is not provisioned, OR
* P1 is a Source Active A-D route whose NLRI contains (C-S,C-G).
Rekhter, et al. Standards Track PAGE 31
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
o VRF B-1 on PE1 exports a UMH-eligible route R2, which is a
matching route for S.
o VRF B-1 on PE1 exports an A-D route P2 whose PTA identifies a
P-tunnel on which VRF B-1 may send traffic whose C-source is S,
where one of the following conditions holds:
* P2 is an I-PMSI A-D route, OR
* P2 is an S-PMSI A-D route whose NLRI specifies (C-*,C-*) or
(C-*,C-G), OR
* P2 is an S-PMSI A-D whose NLRI specifies (C-S,C-G) or
(C-S,C-*), BUT the "single C-source per (C-S,C-G) or (C-S,C-*)
P-tunnel" policy is not provisioned, OR
* P2 is a Source Active A-D route whose NLRI contains (C-S,C-G).
As implied by the rules of Section 4.1, there MUST NOT be any RT that
is common to both R1 and R2. In addition, the following set of rules
for RT assignment MUST be followed when extranets are supported.
These rules support all the extranet transmission models described in
this specification:
o There MUST NOT be any RT that is carried by both P1 and P2.
o The intersection of the set of RTs carried by P1 and the set of
RTs carried by R1 MUST be non-null, and any VRF that imports both
P1 and R1 MUST be configured with an import RT from this
intersection.
o The intersection of the set of RTs carried by P2 and the set of
RTs carried by R2 MUST be non-null, and any VRF that imports both
P2 and R2 MUST be configured with an import RT from this
intersection.
Rekhter, et al. Standards Track PAGE 32
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Suppose that VRF C-1 on PE2 imports P1 and R1 from VRF A-1 while also
importing P2 from VRF B-1. Since
o R1 is VRF C-1's route to S,
o R1 has an RT in common with P1, and
o R1 has no RT in common with P2,
it can be concluded that VRF C-1 should expect that multicast traffic
from S will arrive on the P-tunnel specified in P1. See Sections 6
and 7 for more details on determining the expected P-tunnel for a
given extranet C-flow.
While the assignment of import and export RTs to routes is a
deployment and provisioning issue rather than a protocol issue, it
should be understood that failure to follow these rules is likely to
result in VPN security violations.
5.2. Considerations for Particular Inclusive Tunnel Types
An Inclusive Tunnel (sometimes referred to as an "Inclusive Tree";
see Section 2.1.1 of [RFC 6513]) is a tunnel that, by default, carries
all the multicast traffic of a given MVPN that enters the backbone
network via a particular PE. An Inclusive Tunnel is advertised in
the PTA of an I-PMSI A-D route.
5.2.1. RSVP-TE P2MP or Ingress Replication
This section applies when Inclusive Tunnels are created using either
RSVP-TE P2MP or IR.
Suppose that a VRF, say VRF-S, contains a given extranet C-source
C-S, and VRF-S advertises in its Intra-AS I-PMSI A-D route either a
P2MP RSVP-TE P-tunnel or an IR P-tunnel to carry extranet traffic.
In order for VRF-S to set up the P2MP RSVP-TE or IR P-tunnel, it must
know all the PEs that are leaf nodes of the P-tunnel, and to learn
this it must import an Intra-AS I-PMSI A-D route from every VRF that
needs to receive data through that tunnel.
Therefore, if VRF-R contains an extranet C-receiver that is allowed
by policy to receive extranet flows from C-S, the RT(s) carried by
the Intra-AS I-PMSI A-D routes originated by VRF-R MUST be such that
those Intra-AS I-PMSI A-D routes will be imported into VRF-S.
Rekhter, et al. Standards Track PAGE 33
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
In the case of IR, this has the following consequence: if an egress
PE has n VRFs with receivers for a flow that VRF-S transmits on its
I-PMSI, that egress PE will receive n copies of the same packet, one
for each of the n VRFs.
Note that Section 9.1.1 of [RFC 6514] prohibits the "Leaf Information
Required" flag from being set in the PTA of an Intra-AS I-PMSI A-D
route. If this prohibition is ever removed, the requirement of this
section will apply only if VRF-S does not set that flag.
5.2.2. Ingress Replication
This section applies only when Inclusive Tunnels are created via IR.
[RFC 6513] and [RFC 6514] specify procedures that allow I-PMSIs to be
instantiated by IR. The concept of an IR P-tunnel, and the
procedures for supporting IR P-tunnels, are explained more fully in
[MVPN-IR]. An IR P-tunnel can be thought of as a P2MP tree in which
a packet is transmitted from one node on the tree to another by being
encapsulated and sent through a unicast tunnel.
As discussed in Section 2, when I-PMSIs are used to support
extranets, egress PEs MUST have the ability to discard customer
multicast data packets that arrive on the wrong P-tunnel. When
I-PMSIs are instantiated by IR, this implies that the following two
procedures MUST be followed:
1. One of the following three procedures MUST be followed:
a. the "Single Forwarder Selection" procedures of Section 9.1.2
of [RFC 6513]
b. the "native PIM methods" of Section 9.1.3 of [RFC 6513]
c. the unicast encapsulation used to transmit packets along the
IR P-tunnel is such as to enable the receiving node to
identify the transmitting node (note that this would not be
the case if, for example, the unicast tunnels were MP2P LSPs)
and
2. If a PE assigns an MPLS label value in the PTA of an Intra-AS or
Inter-AS I-PMSI A-D route that it originates, that label value
MUST NOT appear in the PTA of any other I-PMSI or S-PMSI A-D
route originated by the same PE.
Rekhter, et al. Standards Track PAGE 34
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Failure to follow these procedures would make it impossible to
discard packets that arrive on the wrong P-tunnel and thus could lead
to duplication of data.
If it is desired to support extranets while also using IR to
instantiate the PMSIs, an alternative is to use (C-*,C-*) S-PMSIs
instead of I-PMSIs. (See [RFC 6625], as well as Sections 7.2.2,
7.3.2, and 7.4.4 of this document.) This has much the same effect in
the data plane, and there are no restrictions on the type of unicast
tunnel that can be used for instantiating S-PMSIs.
Section 6.4.5 of [RFC 6513] describes a way to support VPNs using
I-PMSIs that are instantiated by IR, using no S-PMSIs, but using
"explicit tracking" to ensure that a C-flow goes only to egress PEs
that have receivers for it. This document does not provide
procedures to support extranets using that model.
6. When PIM Is the PE-PE C-Multicast Control Plane
As specified in [RFC 6513], when PIM is used as the PE-PE C-multicast
control plane for a particular MVPN, there is a "Multidirectional
Inclusive Provider Multicast Service Interface" (MI-PMSI) for that
MVPN, and all the PEs of that MVPN must be able to send and receive
on that MI-PMSI. Associated with each VRF of the MVPN is a PIM
C-instance, and the PIM C-instance treats the MI-PMSI as if it were a
LAN interface. That is, the "ordinary" PIM procedures run over the
MI-PMSI just as they would over a real LAN interface, except that the
data-plane and control-plane "Reverse Path Forwarding (RPF) checks"
need to be modified. Section 5.2 of [RFC 6513] specifies the RPF
check modifications for non-extranet MVPN service.
For example, suppose that there are two VPNs: VPN-S and VPN-R. In
the absence of extranet support, all the VRFs of VPN-S are connected
via one MI-PMSI (call it "the VPN-S MI-PMSI"), and all the VRFs of
VPN-R are connected via another ("the VPN-R MI-PMSI"). If we want to
provide extranet service in which the extranet C-sources are attached
to some set of VPN-S VRFs while the extranet C-receivers are attached
to some set of VPN-R VRFs, then we have two choices:
1. either the VPN-R VRFs need to join the VPN-S MI-PMSI, or
2. the VPN-S VRFs need to join the VPN-R MI-PMSI.
The first choice is used to support the "single PMSI per C-flow"
transmission model. The second choice is used to support the
"multiple PMSIs per C-flow" transmission model.
Rekhter, et al. Standards Track PAGE 35
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Procedures for both models are described below.
To support these models, it must be possible to determine which
I-PMSI A-D routes are associated with the VPN-S I-PMSI and which
I-PMSI A-D routes are associated with the VPN-R I-PMSI. Procedures
are given for assigning RTs to these routes in a way that makes this
determination possible.
Both models allow the use of S-PMSIs to carry multicast data traffic.
If a VRF containing receivers can receive from multiple MI-PMSIs,
each S-PMSI must be uniquely associated with a particular MI-PMSI.
Procedures are given for assigning RTs to these routes in a way that
makes this determination possible.
All the procedures specified in Sections 3, 4, and 5 still apply.
Note that there are no special extranet procedures for Inter-AS
I-PMSI A-D routes or for Leaf A-D routes. Source Active A-D routes
are not used when PIM is the PE-PE C-multicast protocol.
6.1. Provisioning VRFs with RTs
6.1.1. Incoming and Outgoing Extranet RTs
In the absence of extranet service, suppose that each VRF of a given
VPN (call it "VPN-S") is configured with RT-S as its import and
export RT, and that each VRF of a second VPN (call it "VPN-R") is
configured with RT-R as its import and export RT. We will refer to
RT-S and RT-R as "non-extranet RTs".
Now suppose that VPN-S contains some extranet C-sources and VPN-R
contains some extranet C-receivers that are allowed by policy to
receive extranet C-flows from the VPN-S extranet C-sources.
To set up this S-to-R extranet, provisioning an additional RT (call
it "RT-S-to-R") whose value is, in general, distinct from RT-S and
RT-R is REQUIRED.
A VPN-S VRF that contains extranet C-sources allowed to transmit to
VPN-R MUST be configured with RT-S-to-R as an "Outgoing Extranet RT".
A VPN-R VRF that contains extranet C-receivers allowed to receive
packets from VPN-S MUST be configured with RT-S-to-R as an "Incoming
Extranet RT".
Note that the terms "Incoming" and "Outgoing" in this context refer
to the direction of multicast data packets relative to the VRF.
Rekhter, et al. Standards Track PAGE 36
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
The Incoming Extranet RTs and Outgoing Extranet RTs that are
configured for a given VRF serve as import RTs for that VRF. They
also serve as export RTs, but only for specific routes as specified
in Section 6.1.2 below.
Note that any VRF that contains both extranet C-sources and extranet
C-receivers MUST be configured with both Outgoing Extranet RTs and
Incoming Extranet RTs.
A VRF MAY be configured with more than one Incoming Extranet RT
and/or Outgoing Extranet RT.
If it happens to be the case that all C-sources in VPN-S are extranet
C-sources allowed to transmit to VPN-R, then VPN-S VRFs MAY be
configured such that RT-S is both a non-extranet RT and an Outgoing
Extranet RT, and VPN-R VRFs MAY be configured such that RT-S is an
Incoming Extranet RT.
6.1.2. UMH-Eligible Routes and RTs
Suppose that R1 is a route exported from a VPN-S VRF and matching an
extranet C-source that is allowed by policy to transmit to VPN-R. In
that case, R1 MUST carry the Outgoing Extranet RT used for the S-to-R
extranet. This will cause the route to be imported into the VPN-R
VRFs that have extranet C-receivers that are allowed by policy to
receive from VPN-S.
The rules of Section 4 regarding RTs and ambiguous addresses still
apply.
6.1.3. PIM C-Instance Reverse Path Forwarding Determination
Suppose that a PIM control message (call it "M") is received by a
given VRF (call it "VRF-V") from a particular P-tunnel T. In order
to process control message M, the PIM C-instance associated with
VRF-V may need to do an "RPF determination" (see Section 5.2.2 of
[RFC 6513]) for a particular IP prefix S. RPF determination is based
upon the rules for UMH selection as specified in Section 5.1 of
[RFC 6513].
Rekhter, et al. Standards Track PAGE 37
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
This document specifies an additional constraint on the UMH selection
procedure. When doing RPF determination for a PIM control message
received over a P-tunnel, a route matching prefix S is not considered
to be eligible for UMH selection unless there is an RT (call it
"RT1"), configured as one of VRF-V's Outgoing Extranet RTs, such that
the following two conditions both hold:
1. The route matching S is exported from VRF-V carrying RT1, and
2. An I-PMSI A-D route advertising P-tunnel T (in its PTA) has been
imported into VRF-V, and that I-PMSI A-D route carries RT1.
6.2. "Single PMSI per C-Flow" Model
In this model, if a VPN-S VRF has extranet multicast C-sources and a
VPN-R VRF has extranet multicast C-receivers allowed by policy to
receive from the C-sources in the VPN-S VRF, then the VPN-R VRF joins
the MI-PMSI that VPN-S uses for its non-extranet traffic.
6.2.1. Forming the MI-PMSIs
Consider a VPN-S VRF that has extranet C-sources. Per [RFC 6513],
each VPN-S VRF must originate an Intra-AS I-PMSI A-D route containing
a PTA specifying the P-tunnel to be used as part of the VPN-S
MI-PMSI. In the absence of extranet service, this route carries the
VRF's non-extranet RT, RT-S. When extranet service is provided
(using the "single PMSI per C-flow" model), this route MUST also
carry each of the VRF's Outgoing Extranet RTs.
Consider a VPN-R VRF that has extranet C-receivers. Per [RFC 6513],
each VPN-R VRF must originate an Intra-AS I-PMSI A-D route containing
a PTA specifying the P-tunnel to be used as part of the VPN-R
MI-PMSI. This route carries the VRF's non-extranet RT, RT-R. When
extranet service is provided (using the "single PMSI per C-flow"
model), the VPN-R VRF MUST also originate one or more additional
Intra-AS I-PMSI A-D routes. It MUST originate one additional
Intra-AS I-PMSI A-D route for each Incoming Extranet RT with which it
has been configured; each such route will carry exactly one of the
configured Incoming Extranet RTs.
Note that when a VRF originates more than one Intra-AS I-PMSI A-D
route, each of them MUST contain a different RD in its NLRI. In
addition, we add the requirement that any pair of such routes
MUST NOT contain an RT in common.
Rekhter, et al. Standards Track PAGE 38
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
A VRF with extranet C-sources MUST join the P-tunnels advertised in
the imported I-PMSI A-D routes that carry its non-extranet RT or any
of its Outgoing Extranet RTs. This set of P-tunnels will be treated
as instantiating a single MI-PMSI; the associated PIM C-instance will
treat that MI-PMSI as a single LAN and will run PIM procedures on
that LAN, as specified in [RFC 6513]. The fact that the MI-PMSI
attaches to VRFs of different VPNs is not known to the PIM C-instance
of the VRF containing the sources.
A VRF with extranet C-receivers MUST join the P-tunnels advertised in
all the imported I-PMSI A-D routes. The set of P-tunnels advertised
in the I-PMSI A-D routes that carry a particular Incoming Extranet RT
are treated as instantiating a particular MI-PMSI. So, a VRF with
C-receivers will "see" several MI-PMSIs, one corresponding to the
non-extranet, and as many as one for each configured Incoming
Extranet RT. The PIM C-instance associated with the VRF will treat
each of these MI-PMSIs as a separate LAN interface.
As an example, suppose that:
o All VPN-R VRFs are configured with RT-R as a non-extranet import
and export RT, and
o VPN-R VRFs with extranet receivers are configured with RT-S-to-R
as an Incoming Extranet RT, and
o VPN-S VRFs with extranet transmitters are configured with:
* RT-S as a non-extranet import and export RT
* a list of IP addresses that are the addresses of the extranet
sources
* RT-S-to-R as an Outgoing Extranet RT
VPN-S VRFs will then export UMH-eligible routes matching extranet
C-sources, and these routes will carry both RT-S and RT-S-to-R. Each
VPN-S VRF will also export an Intra-AS I-PMSI A-D route that carries
both RT-S and RT-S-to-R.
VPN-R VRFs will originate and export two Intra-AS I-PMSI A-D routes:
one carrying RT-R and one carrying RT-S-to-R. The Intra-AS I-PMSI
A-D route with RT-S-to-R will be imported into the VPN-S VRFs.
VPN-R will regard all the I-PMSI A-D routes it has exported or
imported with RT-S-to-R as part of a single MI-PMSI. VPN-R will
regard all the I-PMSI A-D routes it has exported or imported with
RT-R as part of a second MI-PMSI. The PIM C-instance associated with
Rekhter, et al. Standards Track PAGE 39
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
a VPN-R VRF will treat the two MI-PMSIs as two separate LAN
interfaces. However, the VPN-S VRFs will regard all the I-PMSI A-D
routes imported with RT-S or RT-S-to-R as establishing only a single
MI-PMSI. One can think of this as follows: the VPN-R VRFs have
joined the VPN-S MI-PMSI as well as the VPN-R MI-PMSI.
Extranets consisting of more than two VPNs are easily supported as
follows. Suppose that there are three VPNs: VPN-A, VPN-B, and VPN-C.
VPN-A and VPN-B have extranet C-sources, and VPN-C contains receivers
for both VPN-A extranet C-sources and VPN-B extranet C-sources. In
this case, the VPN-C VRFs that have receivers for both VPN-A and
VPN-B sources may be provisioned as follows. These VPN-C VRFs may be
provisioned with RT-C as a non-extranet RT, and with RT-A-to-C and
RT-B-to-C as Incoming Extranet RTs. In this case, the VPN-C VRFs
that are so provisioned will originate three Intra-AS I-PMSI A-D
routes (each with a different RD in its NLRI), each of which carries
exactly one of the three RTs just mentioned. The VPN-B VRFs with
extranet C-sources will be provisioned with RT-B-to-C as an Outgoing
Extranet RT, and the VPN-A VRFs will be provisioned with RT-A-to-C as
an Outgoing Extranet RT. The result will be that the PIM C-instance
associated with a VPN-C VRF will see three LAN interfaces: one for
the non-extranet and one for each of the two extranets. This
generalizes easily to the case where there are VPN-C receivers in
n different extranets (i.e., receiving extranet flows whose sources
are in n different VPNs).
Suppose again that there are three VPNs -- VPN-A, VPN-B, and VPN-C --
but in this example VPN-A is the only one with extranet sources while
VPN-B and VPN-C both have receivers for the VPN-A extranet sources.
This can be provisioned as either one extranet or two extranets.
To provision it as one extranet, the VPN-A VRFs are configured with
one Outgoing Extranet RT (call it "RT-A-extranet"). The VPN-B and
VPN-C VRFs with extranet receivers will be provisioned with
RT-A-extranet as the Incoming Extranet RT. Thus, the VPN-B and VPN-C
VRFs will each originate two Intra-AS I-PMSI A-D routes: one for the
non-extranet and one for the extranet. From a given VRF, the
Intra-AS I-PMSI A-D route for the extranet will carry RT-A-extranet
but will not share any RT with the non-extranet A-D routes exported
from the same VRF.
The result is that the VPN-B and VPN-C VRFs each belong to two
MI-PMSIs: one for the extranet and one for the intranet. The MI-PMSI
for the extranet attaches VPN-A VRFs, VPN-B VRFs, and VPN-C VRFs.
Rekhter, et al. Standards Track PAGE 40
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Alternatively, one could provision the VPN-A VRFs so that some
UMH-eligible extranet source routes carry an RT that we will call
"RT-A-to-B" and some carry an RT that we will call "RT-A-to-C". The
VPN-A VRFs would be configured with both of these as Outgoing
Extranet RTs. To allow an extranet flow from a VPN-A source to have
both VPN-B and VPN-C receivers, the UMH-eligible route for that
source would carry both RTs. VPN-B VRFs (but not VPN-C VRFs) would
be provisioned with RT-A-to-B as an Incoming Extranet RT. VPN-C VRFs
(but not VPN-B VRFs) would be provisioned with RT-A-to-C as an
Incoming Extranet RT.
Following the rules above, if any VPN-A extranet source is to have
both VPN-B and VPN-C receivers, the VPN-B and VPN-C VRFs will each
originate two I-PMSI A-D routes: one for the extranet and one for the
non-extranet. The single Intra-AS I-PMSI A-D route originated by the
VPN-A VRFs will have both RT-A-to-B and RT-A-to-C among its RTs (as
well as VPN-A's non-extranet RT). The extranet I-PMSI A-D route
originated from a VPN-B VRF would have RT-A-to-B, and the extranet
I-PMSI A-D route originated from a VPN-C VRF would have RT-A-to-C.
If a given VRF contains both extranet C-receivers and extranet
C-sources, the procedures described above still work, as the VRF will
be configured with both Incoming Extranet RTs and Outgoing Extranet
RTs; the VRF functions as both a VPN-S VRF and a VPN-R VRF.
6.2.2. S-PMSIs
When PIM is used as the PE-PE C-multicast control plane, every S-PMSI
is considered to be part of the "emulated LAN" that "corresponds" to
a particular MI-PMSI.
When the bindings of C-flows to particular S-PMSIs are announced via
S-PMSI Join messages (Section 7 of [RFC 6513]) sent on the MI-PMSI,
the S-PMSI is considered to be part of the same LAN interface as the
corresponding MI-PMSI.
When the bindings of C-flows to particular S-PMSIs are announced via
S-PMSI A-D routes, any S-PMSI A-D route exported from that VRF MUST
have an RT in common with exactly one of the Intra-AS A-D routes
exported from that VRF, and this MUST be one of the VRF's Outgoing
Extranet RTs. Further, the S-PMSI A-D route MUST NOT have an RT in
common with any other Intra-AS A-D route exported from a VRF on the
same PE. A given S-PMSI A-D route will be considered to "correspond"
to the MI-PMSI of the Intra-AS I-PMSI A-D route (originated from the
same PE) with which it shares an RT.
Rekhter, et al. Standards Track PAGE 41
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
The MI-PMSI that corresponds to a given S-PMSI is determined as
follows:
o If (1) there is an Intra-AS I-PMSI A-D route originated by the
same PE that originated the S-PMSI A-D route, (2) those two routes
have an RT in common, and (3) that RT is one of the VRF's Incoming
Extranet RTs, then the S-PMSI corresponds to the I-PMSI associated
with that Intra-AS I-PMSI A-D route.
o Otherwise, if (1) there is an Inter-AS I-PMSI A-D route originated
in the same AS as the S-PMSI A-D route, (2) those two routes have
an RT in common, and (3) that RT is one of the VRF's Incoming
Extranet RTs, then the S-PMSI corresponds to the I-PMSI associated
with that Inter-AS I-PMSI A-D route.
o Otherwise, there must be a configuration error (a violation of the
requirements of Sections 3, 4, and 5 of this document).
When wildcard S-PMSIs are used, the rules given in [RFC 6625] for
determining whether a given S-PMSI A-D route is a "match for
reception" to a given (C-S,C-G) or (C-*,C-G) are modified as follows:
A given S-PMSI A-D route MUST NOT be considered to be a "match for
reception" for a given (C-S,C-G) or (C-*,C-G) state UNLESS that
S-PMSI A-D route "corresponds" (as defined above) to the MI-PMSI
that is the incoming interface for the given state.
The rules given in [RFC 6625] for determining whether a given S-PMSI
A-D route is a "match for transmission" are unchanged.
6.2.3. Sending PIM Control Packets
Suppose that a PE, say PE1, receives a PIM Join(S,G) from a CE, over
a VRF interface that is associated with a VPN-R VRF. The PE does the
RPF check for S by looking up S in the VPN-R VRF. The PIM C-instance
associated with that VRF must determine the correct P-tunnel over
which to send a PIM Join(S,G) to other PEs.
To do this, PE1 finds, in the VRF associated with the interface over
which the Join was received, the selected UMH route for S, following
the procedures of Section 5.1 of [RFC 6513]. PE1 determines the set
of RTs carried by that route. PE1 then checks to see if there is an
Intra-AS I-PMSI A-D route, currently originated by PE1, that has an
RT in common with the selected UMH route for S.
Rekhter, et al. Standards Track PAGE 42
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
If the rules of Sections 3, 4, and 5 have been followed, each of
PE1's selected UMH routes will share an RT with a single one of PE1's
currently originated Intra-AS I-PMSI A-D routes. If this is so, the
Join is sent on the P-tunnel advertised in the PTA of that route.
Otherwise, the Join MUST NOT be sent.
In essence, this procedure makes the RPF check for C-S resolve to the
MI-PMSI that is serving as the next-hop "interface" to C-S.
If a PE receives a PIM Join(*,G) from a CE, the procedure for doing
the RPF check is the same, except that the selected UMH route will be
a route to the C-RP associated with the C-G group.
6.2.4. Receiving PIM Control Packets
When a PIM C-instance receives a PIM control message from a P-tunnel,
it needs to identify the message's incoming interface. This incoming
interface is the MI-PMSI of which the P-tunnel is a part.
6.2.5. Sending and Receiving Data Packets
The rules for choosing the PMSI on which to send a multicast data
packet are as specified in [RFC 6513] and [RFC 6625], with one new
restriction: a VPN-S VRF always transmits a multicast data packet
either on the VPN-S MI-PMSI or on an S-PMSI that corresponds to the
VPN-S MI-PMSI. From the perspective of the PIM C-instance, there is
only one outgoing interface.
When a PIM C-instance receives a multicast data packet from a given
P-tunnel and that P-tunnel is being used to instantiate an MI-PMSI,
the MI-PMSI of which the P-tunnel is a part (see Sections 6.2.1 and
6.2.2) is considered to be the packet's incoming interface. If the
packet is received on a P-tunnel that was advertised in an S-PMSI A-D
route, the packet's incoming interface is the MI-PMSI to which that
S-PMSI route corresponds, as defined in Section 6.2.2. Ordinary PIM
rules for data-plane RPF checks apply.
Following ordinary PIM procedures, packets arriving from an
unexpected incoming interface are discarded. This eliminates any
problems due to the ambiguities described in Sections 2.1 and 2.2.
6.3. "Multiple PMSIs per C-Flow" Model
In this model, if a VPN-S VRF has extranet multicast C-sources and a
VPN-R VRF has extranet multicast C-receivers allowed by policy to
receive from the C-sources in the VPN-S VRF, then the VPN-S VRF joins
the MI-PMSI that VPN-R uses for its non-extranet traffic.
Rekhter, et al. Standards Track PAGE 43
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
In the "single PMSI per C-flow" transmission model (as described in
Section 6.2), a PE that needs to transmit a multicast data packet to
a set of other PEs transmits the packet on a single PMSI. This means
that if a packet needs to be transmitted from a VPN-A VRF and
received at a VPN-B VRF and a VPN-C VRF, there must be some P-tunnel
from which the VPN-B and VPN-C VRFs can both receive packets.
In the "multiple PMSIs per C-flow" transmission model, a PE that
needs to transmit a multicast data packet to a set of other PEs may
transmit the packet on several different PMSIs. (Of course, any
given packet is transmitted only once on a given P-tunnel.) For
example, if a C-flow (C-S,C-G) has a VPN-A C-source, a VPN-B
receiver, and a VPN-C receiver, there could be one PMSI that the
VPN-A VRF uses to transmit the packet to the VPN-B VRFs and
another PMSI that the VPN-A VRF uses to transmit the packet to the
VPN-C VRFs.
6.3.1. Forming the MI-PMSIs
Consider a VPN-R VRF that has extranet C-receivers. Per [RFC 6513],
each VPN-R VRF must originate an Intra-AS I-PMSI A-D route containing
a PTA specifying the P-tunnel to be used as part of the VPN-R
MI-PMSI. In the absence of extranet service, this route carries the
VRF's non-extranet RT, RT-R. When extranet service is provided
(using the "single PMSI per C-flow" model), this route MUST also
carry each of the VRF's Incoming Extranet RTs.
Consider a VPN-S VRF that has extranet C-sources. Per [RFC 6513],
each VPN-S VRF must originate an Intra-AS I-PMSI A-D route containing
a PTA specifying the P-tunnel to be used as part of the VPN-S
MI-PMSI. This route carries the VRF's non-extranet RT, RT-S. When
extranet service is provided using the "multiple PMSIs per C-flow"
model, the VPN-S VRF MUST also originate one or more additional
Intra-AS I-PMSI A-D routes. It MUST originate one additional
Intra-AS I-PMSI A-D route for each Outgoing Extranet RT with which it
has been configured; each such route will have a distinct RD and will
carry exactly one of the configured Outgoing Extranet RTs.
As with the "single PMSI per C-flow" transmission model, VRFs
containing extranet C-receivers need to import UMH-eligible extranet
C-source routes from VRFs containing C-sources. This is ensured by
the rules of Sections 3, 4, and 5.
However, in the "multiple PMSIs per C-flow" model, a VRF containing
only C-receivers originates only a single Intra-AS I-PMSI A-D route
carrying the non-extranet RT and all the Incoming Extranet RTs.
Rekhter, et al. Standards Track PAGE 44
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
When a VRF containing C-receivers imports Intra-AS I-PMSI A-D routes
that carry the non-extranet RT or one of the Incoming Extranet RTs,
the P-tunnels specified in the PTA of all such routes are considered
to be part of the same MI-PMSI. That is, the associated PIM
C-instance will treat them as part of a single interface.
In this model, it is the VRF containing extranet C-sources that MUST
originate multiple Intra-AS I-PMSI A-D routes. Each such route MUST
have a distinct RD, and the set of RTs carried by any one of these
routes MUST be disjoint from the set carried by any other. There
MUST be one such route for each of the VRF's Outgoing Extranet RTs,
and each such route MUST carry exactly one of the VRF's Outgoing
Extranet RTs. The VRFs containing extranet C-sources MUST also
import all the A-D routes originated by the VRFs containing extranet
C-receivers. If a set of originated and/or imported Intra-AS I-PMSI
A-D routes have an RT in common and that RT is one of the VRF's
Outgoing Export RTs, then those routes are considered to be "about"
the same MI-PMSI. The PIM C-instance of the VRF treats each MI-PMSI
as a LAN interface.
In effect, if VPN-S has only extranet C-sources and VPN-R has only
extranet C-receivers, this model has the VPN-S VRFs join the VPN-R
MI-PMSI. The VPN-S VRFs will thus be attached to multiple MI-PMSIs,
while the VPN-R VRFs are attached to only one. The fact that the
VPN-R MI-PMSI is attached to VPN-S VRFs is not known to the PIM
C-instance at the VPN-R VRFs.
If a VPN-A VRF has extranet C-sources allowed to send to C-receivers
in a VPN-B VRF and the VPN-B VRF has C-sources allowed to send to
C-receivers in the VPN-A VRF, the above procedures still work as
specified.
Following normal PIM procedures, when the PIM C-instance at a VRF
with extranet C-sources receives a Join(C-S,C-G) or a Join(C-*,C-G)
over an MI-PMSI, it may create (C-S,C-G) or (C-*,C-G) state, and the
MI-PMSI over which the Join was received may be added to the set of
outgoing interfaces for that multicast state. If n MI-PMSIs are
added to the outgoing interface list for a particular multicast
state, a multicast data packet may need to be replicated n times and
transmitted once on each of the n MI-PMSIs.
Since all of the multicast data packets received from another PE are
received over a single emulated LAN, it is not necessary to have any
special procedures to determine a packet's incoming interface. The
ambiguities described in Sections 2.1 and 2.2 do not occur, because a
VPN-R VRF can only receive multicast data traffic that has been
requested by a VPN-R VRF.
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
7. When BGP Is the PE-PE C-Multicast Control Plane
This document assumes that if BGP is used as the PE-PE C-multicast
control plane, the "single PMSI per C-flow" model is used.
Procedures for providing the "multiple PMSIs per C-flow" model with
BGP C-multicast are outside the scope of this document.
When BGP is used as the C-multicast control plane, the "single PMSI
per C-flow" model may be used either with or without extranet
separation. (Recall that "extranet separation" means that no
P-tunnel can carry traffic from both extranet sources and
non-extranet sources.) In either case, the data traffic may be
carried on Inclusive Tunnels only, Selective Tunnels only (known as
the "S-PMSI only" model), or a combination of Inclusive Tunnels and
Selective Tunnels. This is determined by provisioning. The
procedures specified below support all three choices.
Note that there are no special extranet procedures for Inter-AS
I-PMSI A-D routes or for Leaf A-D routes.
7.1. Originating C-Multicast Routes
This section applies whether extranet separation is used or not.
When it is necessary to originate a C-multicast Source Tree Join for
(C-S,C-G), a PE must follow the procedures of Section 11.1.3
("Constructing the Rest of the C-Multicast Route") of [RFC 6514] to
find the selected UMH route for C-S. When it is necessary to
originate a C-multicast Shared Tree Join for (C-*,C-G), where C-G is
an ASM group, a PE must follow the procedures of that section to find
the selected UMH route for C-G's C-RP.
Section 11.1.3 of [RFC 6514] specifies how information from the
selected UMH route is used to find an Intra-AS I-PMSI A-D route or an
Inter-AS I-PMSI A-D route. Information from that I-PMSI A-D route is
then used to construct part of the C-multicast route.
For extranets, the rules given in Section 7.4.5 of this document are
used to find the Inter-AS I-PMSI A-D route or an Intra-AS I-PMSI A-D
route that "corresponds" to the selected UMH route; the rules in
Section 7.4.5 replace the rules given in Section 11.1.3 of [RFC 6514]
for finding the Inter-AS or Intra-AS I-PMSI A-D route.
Information from this I-PMSI A-D route is then used, as specified in
Section 11.1.3 of [RFC 6514], to construct the C-multicast route.
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
7.2. Originating A-D Routes without Extranet Separation
7.2.1. Intra-AS I-PMSI A-D Routes
Consider a VRF (call it "VRF-S") that contains extranet C-sources and
exports UMH-eligible routes matching those C-sources. The VRF may
also originate and export an Intra-AS I-PMSI A-D route.
As specified in [RFC 6514], if exactly one Intra-AS I-PMSI A-D route
is originated by and exported from VRF-S, the RTs carried by that
route MUST be chosen such that every VRF that imports a UMH-eligible
route from VRF-S also imports this Intra-AS I-PMSI A-D route.
If inclusive P-tunnels are being used to carry extranet C-flows,
there are additional requirements on the way the RTs carried by the
Intra-AS I-PMSI A-D routes must be chosen, as specified in the
following paragraph.
If VRF-S is using inclusive P-tunnels but is not using extranet
separation, there is one inclusive P-tunnel rooted at VRF-S, and this
tunnel carries both extranet and non-extranet C-flows. This
Inclusive Tunnel is identified in the PTA of the Intra-AS I-PMSI A-D
route originated from VRF-S. The set of RTs carried by this Intra-AS
I-PMSI A-D route MUST be chosen so as to ensure that every VRF that
imports a UMH-eligible route from this VRF-S also imports this
Intra-AS I-PMSI A-D route. Further, the set of RTs carried by this
Intra-AS I-PMSI A-D route MUST be chosen such that it has at least
one RT in common with every UMH-eligible route that is exported from
the VRF.
7.2.2. S-PMSI A-D Routes
Let R-SP be an S-PMSI A-D route that is exported from VRF-S. Suppose
that R-SP is used to bind some or all of the extranet C-flows from a
given extranet C-source to a given selective P-tunnel. Let R-UMH be
a UMH-eligible route that is exported from VRF-S and matches the
given extranet C-source. In that case, R-SP and R-UMH MUST have at
least one RT in common. Further, the RTs carried by these two routes
MUST be such that every VRF that imports R-UMH also imports R-SP.
These rules apply whether or not R-SP uses wildcards [RFC 6625].
Rekhter, et al. Standards Track PAGE 47
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
An implementation MUST allow the set of RTs carried by the S-PMSI A-D
routes to be specified by configuration. In the absence of such
configuration, an S-PMSI A-D route originated by a given VRF, say
VRF-X, MUST carry a default set of RTs, as specified by the following
rules:
1. By default, an S-PMSI A-D route originated by VRF-X for a given
(C-S,C-G) or (C-S,C-*) carries the same RT(s) as the UMH-eligible
route originated by VRF-X that matches C-S.
2. By default, an S-PMSI A-D route originated by VRF-X for a given
(C-*,C-G) carries as its RTs a set union of all RT(s) of the
UMH-eligible route(s) matching the multicast C-sources contained
in VRF-X that could originate traffic for that C-G. Moreover, if
the VRF contains (as defined in Section 1.1) the C-RP of C-G,
then this set union also includes the RT(s) of the UMH-eligible
route matching C-RP and the RT(s) of the unicast VPN-IP route
matching C-RP.
3. By default, if a (C-*,C-*) S-PMSI A-D route originated by VRF-X
is to be used for both extranet and non-extranet traffic, it
carries the same RTs that would be carried (as specified in
Section 7.2.1) by an I-PMSI A-D route originated by VRF-X if that
I-PMSI A-D route were advertising an inclusive P-tunnel for
carrying both extranet and non-extranet traffic. In general, a
given VRF would not originate both (a) an S-PMSI A-D route
advertising a (C-*,C-*) selective P-tunnel for both extranet and
non-extranet traffic and (b) an I-PMSI A-D route advertising an
inclusive P-tunnel for both extranet and non-extranet traffic, as
the inclusive P-tunnel would not get used in that case.
7.2.3. Source Active A-D Routes
7.2.3.1. When Inter-Site Shared Trees Are Used
This section applies when inter-site shared trees are used, as
specified in Section 13 of [RFC 6514].
If VRF-S exports a Source Active A-D route that contains C-S in the
Multicast Source field of its NLRI and VRF-S also exports a
UMH-eligible route matching C-S, the Source Active A-D route MUST
carry at least one RT in common with the UMH-eligible route. The RT
MUST be chosen such that the following condition holds: if a VRF, say
VRF-R, contains an extranet C-receiver allowed by policy to receive
extranet traffic from C-S, then VRF-R imports both the UMH-eligible
route and the Source Active A-D route.
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
By default, a Source Active A-D route for a given (C-S,C-G), exported
by a given VRF, carries the same set of RTs as the UMH-eligible route
matching C-S that is exported from that VRF.
7.2.3.2. When Inter-Site Shared Trees Are Not Used
This section applies when inter-site shared trees are not used, as
specified in Section 14 of [RFC 6514].
Suppose that a VRF, say VRF-X, contains the C-RP for a given extranet
C-group, say C-G. If C-S is an active source for C-G, then,
following the procedures of Section 14.1 of [RFC 6514], VRF-X may
export a Source Active A-D route that contains C-S in the Multicast
Source field of its NLRI. With the following text, this document
replaces the rule specified in Section 14.1 of [RFC 6514] for
constructing the RT(s) carried by such a route: VRF-X MUST be
configured such that the Source Active A-D route for (C-S,C-G)
carries the same set of RTs as the UMH-eligible route matching C-S
that is exported from the VRF(s) containing C-S. This way, if a VRF,
say VRF-R, contains an extranet C-receiver allowed by policy to
receive extranet traffic from C-S, then VRF-R imports both the
UMH-eligible route and the Source Active A-D route.
7.3. Originating A-D Routes with Extranet Separation
If a VRF contains both extranet C-sources and non-extranet C-sources,
it MUST be configured with both a default RD and an extranet RD (see
Section 1.3). The use of these RDs is explained in the following
subsections.
7.3.1. Intra-AS I-PMSI A-D Routes
This section applies when VRF-S is using extranet separation AND when
VRF-S is using an inclusive P-tunnel to carry some or all of the
extranet C-flows that it needs to transmit to other VRFs.
If VRF-S contains both extranet C-sources and non-extranet C-sources,
and inclusive P-tunnels are used to carry both extranet C-flows and
non-extranet C-flows, then there MUST be two Inclusive Tunnels from
VRF-S, one of which is to be used only to carry extranet C-flows (the
"extranet inclusive P-tunnel") and one of which is to be used only to
carry non-extranet C-flows (the "non-extranet inclusive P-tunnel").
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
In this case, the VRF MUST originate two Intra-AS I-PMSI A-D routes.
Their respective NLRIs MUST of course have different RDs. One of the
Intra-AS I-PMSI A-D routes identifies the extranet inclusive P-tunnel
in its PTA. This route MUST have the VRF's extranet RD in its NLRI.
The other route identifies the non-extranet inclusive P-tunnel in its
PTA. This route MUST have the VRF's default RD in its PTA.
If VRF-S uses an inclusive P-tunnel for carrying extranet traffic but
does not use an inclusive P-tunnel for carrying non-extranet traffic,
then of course only a single Intra-AS I-PMSI A-D route need be
originated. The PTA of this route identifies the "extranet inclusive
P-tunnel". The NLRI of that route MUST contain the VRF's
extranet RD.
An Intra-AS I-PMSI A-D route whose PTA identifies an extranet
inclusive P-tunnel MUST carry the Extranet Separation Extended
Community defined in Section 4.5.
The RTs carried by an Intra-AS I-PMSI A-D route whose PTA identifies
the "extranet inclusive P-tunnel" MUST be chosen such that the
following condition holds: if a VRF (call it "VRF-R") imports a
UMH-eligible route from VRF-S and that route matches an extranet
C-source, then VRF-R also imports that Intra-AS I-PMSI A-D route.
Note that when extranet separation is used, it is possible to use an
inclusive P-tunnel for non-extranet traffic while using only
selective P-tunnels for extranet traffic. It is also possible to use
an inclusive P-tunnel for extranet traffic while using only selective
P-tunnels for non-extranet traffic.
7.3.2. S-PMSI A-D Routes
Let R-SP be an S-PMSI A-D route that is exported from VRF-S. Suppose
that R-SP is used to bind some or all of the extranet C-flows from a
given extranet C-source to a given selective P-tunnel. Let R-UMH be
a UMH-eligible route that is exported from VRF-S and matches the
given extranet C-source. In that case, R-SP and R-UMH MUST have at
least one RT in common. Further, the RTs carried by these two routes
MUST be such that every VRF that imports R-UMH also imports R-SP.
These rules apply whether or not R-SP uses wildcards [RFC 6625].
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
The following rules, specific to the use of extranet separation,
apply:
o A selective P-tunnel MUST NOT carry C-flows from both extranet and
non-extranet C-sources.
o If it is desired to use a (C-*,C-*) S-PMSI to carry extranet
traffic and also use a (C-*,C-*) S-PMSI to carry non-extranet
traffic, then two (C-*,C-*) S-PMSI A-D routes MUST be originated.
These two routes MUST have different RDs in their respective NLRI
fields, and their respective PTAs MUST identify different
P-tunnels. If the route advertises a P-tunnel that carries only
non-extranet traffic, the route's NLRI MUST contain the VRF's
default RD. If the route advertises a P-tunnel that carries only
extranet traffic, the route's NLRI MUST contain the VRF's
extranet RD.
o In the following cases, an S-PMSI A-D route exported from the VRF
MUST have the VRF's extranet RD in its NLRI:
* The S-PMSI A-D route is a (C-S,C-G) or a (C-S,C-*) S-PMSI A-D
route, and C-S is an extranet C-source.
* The S-PMSI A-D route is a (C-*,C-G) S-PMSI A-D route, and C-G
is an extranet C-group.
In all other cases, a (C-S,C-G), (C-S,C-*), or (C-*,C-G) S-PMSI
A-D route MUST have the VRF's default RD in its NLRI.
o A (C-*,C-*) S-PMSI A-D route advertising a P-tunnel that is used
to carry extranet traffic MUST carry the Extranet Separation
Extended Community defined in Section 4.5.
An implementation MUST allow the set of RTs carried by the S-PMSI A-D
routes to be specified by configuration. In the absence of such
configuration, an S-PMSI A-D route originated by a given VRF, say
VRF-X, MUST carry a default set of RTs, as specified by the following
rules:
1. Rule 1 of Section 7.2.2 applies.
2. By default, if C-G is an extranet C-group, rule 2 of
Section 7.2.2 applies.
3. By default, if a (C-*,C-*) S-PMSI A-D route originated by VRF-X
is to be used for extranet traffic, it carries the same RTs that
would be carried (as specified in Section 7.3.1) by an I-PMSI A-D
route originated by VRF-X if that I-PMSI A-D route were
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advertising an inclusive P-tunnel for carrying extranet traffic.
In general, a given VRF would not originate both an S-PMSI A-D
route advertising a (C-*,C-*) selective P-tunnel for extranet
traffic and an I-PMSI A-D route advertising an inclusive P-tunnel
for extranet traffic, as the inclusive P-tunnel would not get
used in that case.
7.3.3. Source Active A-D Routes
The procedures of Section 7.2.3 apply.
However, if a Source Active A-D route is exported from a given VRF
and the route contains C-S, where C-S is an extranet C-source, then
the RD of the route's NLRI MUST be the extranet RD of the VRF.
Otherwise, the RD is the default RD of the VRF.
7.4. Determining the Expected P-Tunnel for a C-Flow
This section applies whether extranet separation is used or not.
In the context of a VRF with receivers for a particular C-flow, a PE
must determine the P-tunnel over which packets of that C-flow are
expected to arrive. This is done by finding an I-PMSI or S-PMSI A-D
route that "matches" the flow. The matching A-D route will contain a
PTA that specifies the P-tunnel being used to carry the traffic of
that C-flow. We will refer to this P-tunnel as the "expected
P-tunnel" for the C-flow. (Note that, per [MVPN-IR], if the PTA
specifies a tunnel of type "Ingress Replication" (IR), the identifier
of the P-tunnel is actually the NLRI of the I-PMSI or S-PMSI A-D
route. If the PTA specifies a tunnel type other than IR, the
identifier of the P-tunnel is found in the Tunnel Identifier field of
the PTA.)
A PE that needs to receive a given (C-S,C-G) or (C-*,C-G) C-flow MUST
join the expected P-tunnel for that C-flow, and the PE MUST remain
joined to the P-tunnel as long as (1) the PE continues to need to
receive the given C-flow and (2) the P-tunnel continues to remain the
expected P-tunnel for that C-flow. Procedures for joining and
leaving a tunnel depend, of course, on the tunnel type.
If a PTA specifies a non-zero MPLS label for a tunnel that is not an
IR tunnel, then the PE originating the A-D route containing that PTA
is advertising an aggregate P-tunnel. The aggregate P-tunnel can be
thought of as an outer P-tunnel multiplexing some number of inner
P-tunnels. The inner P-tunnels are demultiplexed by means of the
MPLS label in the PTA. In this document, when we talk of the
"expected P-tunnel" in the context of an aggregate P-tunnel, we refer
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
to a particular inner P-tunnel, not to the outer P-tunnel. It is
this "inner P-tunnel" that is the expected P-tunnel for a given
C-flow.
In order to find the expected P-tunnel for a given C-flow, the
upstream PE of the C-flow is first determined. Then, the S-PMSI A-D
routes originated by that PE are examined, and their NLRIs compared
to the (C-S/C-RP,C-G) of the flow, to see if there is a "match for
reception". (If there is no S-PMSI A-D route that matches a given
C-flow, the expected P-tunnel for that C-flow may have been
advertised in an I-PMSI A-D route; see Section 7.4.5.)
The rules for determining, in non-extranet cases, whether a given
C-flow is a "match for reception" for a given S-PMSI A-D route are
given in Section 3.2 of [RFC 6625]. Note that we use the terms
"installed" and "originated" as they are defined in Section 3.2 of
[RFC 6625]. (See also Section 1.1 of this document.)
This specification provides additional rules for determining whether
a given S-PMSI A-D route is a "match for reception" for a given
(C-S/C-RP,C-G). Note that these rules all assume the context of a
particular VRF into which the A-D route has been imported.
The rules given in [RFC 6625] for determining whether a given S-PMSI
A-D route is a "match for transmission" remain unchanged.
Suppose that a PE has originated a C-multicast Shared Tree Join for
(C-*,C-G) but has not originated a C-multicast Source Tree Join for
(C-S,C-G). Suppose also that the PE has received and installed a
Source Active A-D route for (C-S,C-G). As described in Section 13.2
of [RFC 6514], the PE must receive the (C-S,C-G) traffic from the
tunnel the originator of the installed Source Active A-D route uses
for sending (C-S,C-G).
The originator of the installed Source Active A-D route is determined
as follows:
1. Look at the "UMH Route Candidate Set" for C-S, as defined in
Section 5.1.3 of [RFC 6513].
2. From that set, select a subset of UMH routes to C-S, such that
each route in the subset has at least one RT in common with the
Source Active A-D route and at least one of the RTs in common is
an import RT of the VRF.
3. From that subset, find the route whose RD is the same as the RD
from the NLRI of the Source Active A-D route.
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
4. The upstream PE is the PE identified in the VRF Route Import
Extended Community of that route.
5. The upstream AS is the AS identified in the Source AS Extended
Community of that route.
If step 2 results in an empty set or step 3 fails to find a route,
then the upstream PE of the Source Active A-D route cannot be
determined, and it is necessary to act as if the Source Active A-D
route had not been installed. (A subsequent change to the UMH Route
Candidate Set for C-S may require that a new attempt be made to
determine the upstream PE.)
Once the upstream PE is determined, the P-tunnel over which the flow
is expected is determined according to the procedures already
described in this section.
7.4.1. (C-S,C-G) S-PMSI A-D Routes
When extranet functionality is being provided, an S-PMSI A-D route
whose NLRI contains (C-S,C-G) is NOT considered to be a "match for
reception" for a given C-flow (C-S,C-G) unless one of the following
conditions holds (in addition to the conditions specified in
[RFC 6625]):
o the "single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" is
provisioned, or
o the selected UMH route for C-S has at least one RT in common with
the S-PMSI A-D route, and at least one of the common RTs is an
import RT of the VRF.
7.4.2. (C-S,C-*) S-PMSI A-D Routes
When extranet functionality is being provided, an S-PMSI A-D route
whose NLRI contains (C-S,C-*) is NOT considered to be a "match for
reception" for a given C-flow (C-S,C-G) unless one of the following
conditions holds (in addition to the conditions specified in
[RFC 6625]):
o the "single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" is
provisioned, or
o the selected UMH route for C-S has at least one RT in common with
the S-PMSI A-D route, and at least one of the common RTs is an
import RT of the VRF.
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
7.4.3. (C-*,C-G) S-PMSI A-D Routes
When extranet functionality is being provided, an S-PMSI A-D route
whose NLRI contains (C-*,C-G) is NOT considered to be a "match for
reception" for a given C-flow (C-S,C-G) in a given VRF unless either
condition 1 or condition 2 below holds (in addition to the conditions
specified in [RFC 6625]):
1. The given VRF has currently originated a C-multicast Shared Tree
Join route for (C-*,C-G), and
a. (C-*,C-G) matches an installed (C-*,C-G) S-PMSI A-D route
(according to [RFC 6625]) in the given VRF, and
b. either
i. the "single C-group per (C-*,C-G) P-tunnel" policy has
been provisioned, or
ii. the RTs of that S-PMSI A-D route form a non-empty
intersection with the RTs carried in the VRF's
selected UMH route for C-RP of that C-G, or
iii. installed in the VRF is at least one (C-S,C-G) Source
Active A-D route that was originated by the same PE as
the (C-*,C-G) S-PMSI A-D route.
2. The given VRF does not have a currently originated C-multicast
Shared Tree Join for (C-*,C-G), but
a. there are one or more values for C-S for which the VRF has a
currently originated Source Tree Join C-multicast route for
(C-S,C-G), and
b. the (C-* C-G) S-PMSI A-D route matches (according to
[RFC 6625]) each such (C-S,C-G), and
c. either
i. the "single C-group per (C-*,C-G) P-tunnel" policy has
been provisioned, or
ii. the RTs of that S-PMSI A-D route form a non-empty
intersection with the RTs carried in the VRF's selected
UMH routes for each such C-S
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If a VRF has an installed (C-*,C-G) S-PMSI A-D route but does not
have a (C-S,C-G) or (C-*,C-G) multicast state that matches that
route for reception, the procedures of Section 12.3 ("Receiving
S-PMSI A-D Routes by PEs") of [RFC 6514] are not invoked for that
route. If those multicast states are created at some later time
when the route is still installed, the procedures of Section 12.3
of [RFC 6514] are invoked at that time.
7.4.4. (C-*,C-*) S-PMSI A-D Routes
A (C-*,C-*) S-PMSI A-D route (call it "R-AD") is NOT considered to be
a "match for reception" for a given C-flow (C-S,C-G) or (C-*,C-G)
unless the following conditions hold (in addition to the conditions
specified in [RFC 6625]):
o The selected UMH route (call it "R-UMH") for C-S or for C-G's
C-RP, respectively, has at least one RT in common with R-AD, and
at least one of the common RTs is an import RT of the VRF.
o Either R-AD and R-UMH both carry the Extranet Separation Extended
Community or neither carries the Extranet Separation Extended
Community.
7.4.5. I-PMSI A-D Routes
If a particular egress VRF in a particular egress PE contains no
matching S-PMSI A-D routes for a particular C-flow, then the C-flow
is expected to arrive (at that egress VRF) on an inclusive P-tunnel.
Suppose that an egress PE has originated a (C-S,C-G) C-multicast
Source Tree Join. Let R-UMH be the selected UMH route (in the given
egress VRF) for C-S. As specified in [RFC 6514], the selected
upstream PE for (C-S,C-G) is determined from the VRF Route Import
Extended Community of R-UMH, and the "selected upstream AS" for the
flow is determined from the Source AS Extended Community of R-UMH.
Suppose that an egress PE has originated a (C-*,C-G) C-multicast
Shared Tree Join but has not originated a (C-S,C-G) C-multicast
Source Tree Join. If the egress VRF does not have a (C-S,C-G) Source
Active A-D route installed, the selected upstream PE is determined
from the VRF Route Import Extended Community of the installed
UMH-eligible route matching C-RP, where C-RP is the RP for the group
C-G. The selected upstream AS for the flow is determined from the
Source AS Extended Community of that route. If the egress VRF does
have a (C-S,C-G) Source Active A-D route installed, the selected
upstream PE and upstream AS are determined as specified in
Section 7.4. In either case, let R-UMH be the installed UMH-eligible
route matching C-S.
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
The inclusive P-tunnel that is expected to be carrying a particular
C-flow is found as follows:
o If the selected upstream AS is the local AS or segmented Inter-AS
P-tunnels are not being used to instantiate I-PMSIs, then look in
the VRF for an installed Intra-AS I-PMSI A-D route, R-AD, such
that (a) R-AD is originated by the selected upstream PE, (b) R-AD
has at least one RT in common with R-UMH, (c) at least one of the
common RTs is an import RT of the local VRF, and (d) either R-AD
and R-UMH both carry the Extranet Separation Extended Community or
neither carries the Extranet Separation Extended Community.
The PTA of R-AD specifies the P-tunnel over which the traffic of
the given C-flow is expected.
o If the selected upstream AS is not the local AS and segmented
Inter-AS P-tunnels are being used to instantiate I-PMSIs, then
look in the VRF for an installed Inter-AS I-PMSI A-D route, R-AD,
such that (a) the Source AS field of R-AD's NLRI contains the AS
number of the selected upstream AS, (b) R-AD has at least one RT
in common with R-UMH, (c) at least one of the common RTs is an
import RT of the local VRF, and (d) either R-AD and R-UMH both
carry the Extranet Separation Extended Community or neither
carries the Extranet Separation Extended Community.
The PTA of R-AD specifies the P-tunnel over which the traffic of
the given C-flow is expected.
7.5. Packets Arriving from the Wrong P-Tunnel
Any packets that arrive on a P-tunnel other than the expected
P-tunnel (as defined in Section 7.4) MUST be discarded unless it is
known that all the packets carried by both P-tunnels are from the
same ingress VRF. (See Section 2.3.1 for a more detailed discussion
of when to discard packets from other than the expected P-tunnel.)
Note that packets arriving on the wrong P-tunnel are to be discarded
even if they are arriving from the expected PE.
8. Multiple Extranet VRFs on the Same PE
When multiple VRFs that contain extranet receivers for a given
extranet source are present on the same PE, this PE becomes a single
leaf of the P-tunnel used for sending (multicast) traffic from that
source to these extranet receivers. The PE MUST be able to replicate
this traffic to the multiple VRFs. Specific procedures for doing so
are local to the PE and are outside the scope of this document.
Rekhter, et al. Standards Track PAGE 57
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Two or more VRFs on the same PE may import the same S-PMSI A-D route.
If this S-PMSI A-D route contains a PTA that has its "Leaf
Information Required" flag set, it may be necessary for the PE to
originate a Leaf A-D route whose NLRI is computed from the NLRI of
the S-PMSI A-D route. (Details are provided in [RFC 6514].) Note
that for a given S-PMSI A-D route, the PE can originate only one
corresponding Leaf A-D route, even if the S-PMSI A-D route is
imported into multiple VRFs. This Leaf A-D route can thus be thought
of as originating from several VRFs. It MUST NOT be withdrawn by the
PE until there are no longer any VRFs originating it.
[RFC 6514] specifies conditions under which a PE originates a
C-multicast Source Tree Join or a C-multicast Shared Tree Join, based
on the (*,G) and (S,G) states associated with a given VRF. It also
specifies the procedure for computing the NLRI of each such route.
While a given PE may contain two or more VRFs that have (extranet)
receivers for the same extranet C-flow, the PE cannot originate more
than one BGP route with a given NLRI. If there are multiple VRFs,
each of which has state that is sufficient to cause a given
C-multicast route to be originated, the route can be thought of as
originating from several VRFs. It MUST NOT be withdrawn by the PE
until there is no longer any VRF with multicast state sufficient to
cause the route to be originated.
For a given extranet, the site(s) that contains the extranet
source(s) and the site(s) that contains the extranet receiver(s) may
be connected to the same PE. In this scenario, the procedures by
which (multicast) traffic from these sources is delivered to these
receivers are local to the PE and are outside the scope of this
document.
An implementation MUST support multiple extranet VRFs on a PE.
9. IANA Considerations
IANA has allocated two new codepoints from the "First Come First
Served" [RFC 5226] range of the "Transitive Opaque Extended Community
Sub-Types" registry (under the top-level registry "Border Gateway
Protocol (BGP) Extended Communities" registry).
o Extranet Source Extended Community (0x04)
o Extranet Separation Extended Community (0x05)
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RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
10. Security Considerations
The security considerations of [RFC 6513] and [RFC 6514] are
applicable.
As is the case with any application of technology based upon
[RFC 4364], misconfiguration of the RTs may result in VPN security
violations (i.e., may result in a packet being delivered to a VPN
where, according to policy, it is not supposed to go).
In those cases where the set of extranet sources of a particular VRF
are manually configured, improper configuration of the VRF can result
in VPN security violations -- traffic from a host that is not an
extranet source may be treated as if it were traffic from an extranet
source.
Section 4.4 specifies the optional use of a new Extended Community --
the Extranet Source Extended Community. Security considerations
regarding the use and distribution of that Extended Community are
discussed in that section.
The procedures of this document do not provide encryption of the data
flows that are sent across the SP backbone network. Hence, these
procedures do not by themselves ensure the privacy or integrity of
the data against attacks on the backbone network.
In general, different VPNs are allowed to have overlapping IP address
spaces; i.e., a host in one VPN may have the same IP address as a
host in another. This is safe because the customer routes from a
given VPN do not pass into other VPNs. Even if there are overlapping
address spaces among VPNs, the routes that are known at any given VPN
site are unambiguous, as long as the address space of that VPN is
unambiguous. However, this is not necessarily true when extranet
service is provided. If an extranet C-receiver in VPN-R is to be
able to receive multicast traffic from an extranet C-source in VPN-S,
then the address of the VPN-S extranet C-source must be imported into
one or more VPN-R VRFs. If that address is also the address of a
VPN-R non-extranet C-source, then a system attempting to receive an
extranet C-flow from the VPN-R extranet C-source may instead receive
a non-extranet C-flow from the VPN-S C-source. Otherwise, a VPN
security violation may result.
That is, when provisioning an extranet between two VPNs that have
overlapping address spaces, one must ensure that the IP addresses of
the extranet sources and the extranet receivers are not from the
overlapping part of the address space. This document specifies that
if a route is imported into a given VRF, all addresses that match
that route must be unambiguous in the context of that VRF. Improper
Rekhter, et al. Standards Track PAGE 59
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
provisioning of the extranet source addresses or improper
provisioning of the RTs may cause this rule to be violated and may
result in a VPN security violation.
It is possible that a given multicast C-source is the source of
multiple flows, some of which are intended to be extranet C-flows and
some of which are intended to be non-extranet flows. However, the
procedures of this document will allow any C-receiver that is able to
receive the extranet C-flows from a given C-source to also receive
the non-extranet C-flows from that source. As a result, VPN security
violations may result if any system is a C-source for both extranet
and non-extranet C-flows. However, the set of C-flows transmitted by
a given C-source is not under the control of the SP. SPs who offer
the extranet MVPN service must make sure that this potential for VPN
security violations is clearly understood by the customers who
administer the C-sources.
This specification does not require that UMH-eligible routes be "host
routes"; they may be less specific routes. So, it is possible for
the NLRI of a UMH-eligible route to contain an address prefix that
matches the address of both an extranet C-source and a non-extranet
C-source. If such a route is exported from a VPN-S VRF and imported
by a VPN-R VRF, C-receivers contained in VPN-R will be able to
receive C-flows from the non-extranet C-sources whose addresses match
that route. This may result in VPN security violations. Service
providers who offer the extranet MVPN service must make sure that
this is clearly understood by the customers who administer the
distribution of routes from CE routers to PE routers.
If the address ambiguities described in Sections 2.1 and 2.2 are not
prohibited by deployment of the policies described in Section 2.3.2,
VRFs must be able to discard traffic that arrives on the wrong
P-tunnel (as specified in Sections 2.3.1 and 7.5). Otherwise, VPN
security violations may occur.
Rekhter, et al. Standards Track PAGE 60
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
11. References
11.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<http://www.rfc-editor.org/info/RFC 2119>.
[RFC 4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC 4360,
February 2006, <http://www.rfc-editor.org/info/RFC 4360>.
[RFC 4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC 4364,
February 2006, <http://www.rfc-editor.org/info/RFC 4364>.
[RFC 6513] Rosen, E., Ed., and R. Aggarwal, Ed., "Multicast in
MPLS/BGP IP VPNs", RFC 6513, DOI 10.17487/RFC 6513,
February 2012, <http://www.rfc-editor.org/info/RFC 6513>.
[RFC 6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC 6514, February 2012,
<http://www.rfc-editor.org/info/RFC 6514>.
[RFC 6625] Rosen, E., Ed., Rekhter, Y., Ed., Hendrickx, W., and R.
Qiu, "Wildcards in Multicast VPN Auto-Discovery Routes",
RFC 6625, DOI 10.17487/RFC 6625, May 2012,
<http://www.rfc-editor.org/info/RFC 6625>.
[RFC 7153] Rosen, E. and Y. Rekhter, "IANA Registries for BGP
Extended Communities", RFC 7153, DOI 10.17487/RFC 7153,
March 2014, <http://www.rfc-editor.org/info/RFC 7153>.
[RFC 7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC 7761,
March 2016, <http://www.rfc-editor.org/info/RFC 7761>.
Rekhter, et al. Standards Track PAGE 61
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
11.2. Informative References
[MVPN-IR] Rosen, E., Ed., Subramanian, K., and Z. Zhang, "Ingress
Replication Tunnels in Multicast VPN", Work in Progress,
draft-ietf-bess-ir-03, April 2016.
[RFC 3446] Kim, D., Meyer, D., Kilmer, H., and D. Farinacci, "Anycast
Rendevous Point (RP) mechanism using Protocol Independent
Multicast (PIM) and Multicast Source Discovery Protocol
(MSDP)", RFC 3446, DOI 10.17487/RFC 3446, January 2003,
<http://www.rfc-editor.org/info/RFC 3446>.
[RFC 3618] Fenner, B., Ed., and D. Meyer, Ed., "Multicast Source
Discovery Protocol (MSDP)", RFC 3618,
DOI 10.17487/RFC 3618, October 2003,
<http://www.rfc-editor.org/info/RFC 3618>.
[RFC 4610] Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
Independent Multicast (PIM)", RFC 4610,
DOI 10.17487/RFC 4610, August 2006,
<http://www.rfc-editor.org/info/RFC 4610>.
[RFC 4875] Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
Yasukawa, Ed., "Extensions to Resource Reservation
Protocol - Traffic Engineering (RSVP-TE) for Point-to-
Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
DOI 10.17487/RFC 4875, May 2007,
<http://www.rfc-editor.org/info/RFC 4875>.
[RFC 5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast
(BIDIR-PIM)", RFC 5015, DOI 10.17487/RFC 5015,
October 2007, <http://www.rfc-editor.org/info/RFC 5015>.
[RFC 5059] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas,
"Bootstrap Router (BSR) Mechanism for Protocol Independent
Multicast (PIM)", RFC 5059, DOI 10.17487/RFC 5059,
January 2008, <http://www.rfc-editor.org/info/RFC 5059>.
Rekhter, et al. Standards Track PAGE 62
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
[RFC 5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC 5226, May 2008,
<http://www.rfc-editor.org/info/RFC 5226>.
[RFC 6388] Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
Thomas, "Label Distribution Protocol Extensions for Point-
to-Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, DOI 10.17487/RFC 6388, November 2011,
<http://www.rfc-editor.org/info/RFC 6388>.
Rekhter, et al. Standards Track PAGE 63
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Acknowledgments
The authors wish to thank DP Ayyadevara, Robert Kebler, Padmini
Misra, Rayen Mohanty, Maria Napierala, Karthik Subramanian, and Kurt
Windisch for their contributions to this work.
We also wish to thank Lizhong Jin and Rishabh Parekh for their
reviews and comments.
Special thanks to Jeffrey (Zhaohui) Zhang for his careful review and
for providing the ASCII art appearing in Section 2.
Contributors
Below is a list of other contributing authors, in alphabetical order:
Wim Henderickx
Nokia
Copernicuslaan 50
Antwerp 2018
Belgium
Email: wim.henderickx@nokia.com
Praveen Muley
Nokia
Email: Praveen.Muley@nokia.com
Ray Qiu
Juniper Networks, Inc.
1194 North Mathilda Avenue
Sunnyvale, CA 94089
United States
Email: rqiu@juniper.net
IJsbrand Wijnands
Cisco Systems, Inc.
De Kleetlaan 6a
Diegem 1831
Belgium
Email: ice@cisco.com
Rekhter, et al. Standards Track PAGE 64
RFC 7900 Extranet Multicast in BGP/IP MPLS VPNs June 2016
Authors' Addresses
Yakov Rekhter (editor)
Juniper Networks, Inc.
1194 North Mathilda Avenue
Sunnyvale, CA 94089
United States
Eric C. Rosen (editor)
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts 01886
United States
Email: erosen@juniper.net
Rahul Aggarwal
Arktan
Email: raggarwa_1@yahoo.com
Yiqun Cai
Alibaba Group
400 S El Camino Real #400
San Mateo, CA 94402
United States
Email: yiqun.cai@alibaba-inc.com
Thomas Morin
Orange
2 Avenue Pierre-Marzin
22307 Lannion Cedex
France
Email: thomas.morin@orange.com
Rekhter, et al. Standards Track PAGE 65
RFC TOTAL SIZE: 155704 bytes
PUBLICATION DATE: Wednesday, June 22nd, 2016
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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