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IETF RFC 8556
Last modified on Monday, April 8th, 2019
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Internet Engineering Task Force (IETF) E. Rosen, Ed.
Request for Comments: 8556 M. Sivakumar
Category: Standards Track T. Przygienda
ISSN: 2070-1721 Juniper Networks, Inc.
S. Aldrin
Google, Inc.
A. Dolganow
Nokia
April 2018
Multicast VPN Using Bit Index Explicit Replication (BIER)
 Abstract
The Multicast Virtual Private Network (MVPN) specifications require
the use of multicast tunnels ("P-tunnels") that traverse a service
provider's backbone network. The P-tunnels are used for carrying
multicast traffic across the backbone. A variety of P-tunnel types
are supported. Bit Index Explicit Replication (BIER) is a new
architecture that provides optimal multicast forwarding through a
"multicast domain", without requiring intermediate routers to
maintain any per-flow state or to engage in an explicit tree-building
protocol. This document specifies the protocol and procedures that
allow MVPN to use BIER as the method of carrying multicast traffic
over a service provider's backbone network.
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
https://www.rfc-editor.org/info/RFC 8556.
Rosen, et al. Standards Track PAGE 1 
RFC 8556 MVPN with BIER April 2018
Copyright Notice
Copyright (c) 2018 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
(https://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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Use of the PMSI Tunnel Attribute in x-PMSI A-D Routes . . . . 5
2.1. MPLS Label . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Explicit Tracking . . . . . . . . . . . . . . . . . . . . 9
2.2.1. Using the LIR Flag . . . . . . . . . . . . . . . . . 10
2.2.2. Using the LIR-pF Flag . . . . . . . . . . . . . . . . 10
3. Use of the PMSI Tunnel Attribute in Leaf A-D Routes . . . . . 11
4. Data Plane . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Encapsulation and Transmission . . . . . . . . . . . . . 12
4.2. Disposition . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.1. At a BFER That Is an Egress PE . . . . . . . . . . . 14
4.2.2. At a BFER That Is a P-tunnel Segmentation Boundary . 14
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Normative References . . . . . . . . . . . . . . . . . . 15
7.2. Informative References . . . . . . . . . . . . . . . . . 16
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 16
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
Rosen, et al. Standards Track PAGE 2
RFC 8556 MVPN with BIER April 2018
1. Introduction
[RFC 6513] and [RFC 6514] specify the protocols and procedures that a
Service Provider (SP) can use to provide Multicast Virtual Private
Network (MVPN) service to its customers. Multicast tunnels are
created through an SP's backbone network; these are known as
"P-tunnels". The P-tunnels are used for carrying multicast traffic
across the backbone. The MVPN specifications allow the use of
several different kinds of P-tunnel technology.
Bit Index Explicit Replication (BIER) ([RFC 8279]) is an architecture
that provides optimal multicast forwarding through a "multicast
domain", without requiring intermediate routers to maintain any per-
flow state or to engage in an explicit tree-building protocol. The
purpose of the current document is to specify the protocols and
procedures needed in order to provide MVPN service using BIER to
transport the multicast traffic over the backbone.
Although BIER does not explicitly build and maintain multicast
tunnels, one can think of BIER as using a number of implicitly
created tunnels through a "BIER domain". In particular, one can
think of there as being one Point-to-Multipoint (P2MP) tunnel from
each Bit Forwarding Ingress Router (BFIR) to all the Bit Forwarding
Egress Routers (BFERs) in the BIER domain, where a BIER domain is
generally co-extensive with an IGP network. These "tunnels" are not
specific to any particular VPN. However, the MVPN architecture
provides protocols and procedures that allow the traffic of multiple
MVPNs to be aggregated on a single P-tunnel. In this document, we
specify how to use these multi-VPN aggregation procedures to enable
BIER to transport traffic from multiple MVPNs.
MVPN traffic must sometimes traverse more than one IGP domain,
whereas BIER only carries multicast traffic within a single IGP
domain. However, the MVPN specifications allow P-tunnels to be
segmented (the concept of MVPN segmentation is defined in [RFC 6513]
and [RFC 6514]), where the segmentation points may either be
Autonomous System Border Routers (ASBRs) as described in [RFC 6514],
or Area Border Routers (ABRs) as described in [RFC 7524]. As long as
the segmentation points are capable of acting as BFIRs and BFERs,
BIER can be used to provide some or all of the segments of a
P-tunnel.
Procedures to support MVPN customers who are using Bidirectional PIM
(BIDIR-PIM) are outside the scope of this document.
Rosen, et al. Standards Track PAGE 3
RFC 8556 MVPN with BIER April 2018
This document uses the following terminology from [RFC 8279]:
o BFR: Bit-Forwarding Router.
o BFIR: Bit-Forwarding Ingress Router.
o BFER: Bit-Forwarding Egress Router.
This document uses the following terminology from [RFC 6513]:
o MVPN: Multicast Virtual Private Network -- a VPN [RFC 4364] in
which multicast service is offered.
o P-tunnel: A multicast tunnel through the network of one or more
SPs. P-tunnels are used to transport MVPN multicast data
o PMSI: Provider Multicast Service Interface. PMSI is an
abstraction that represents a multicast service for carrying
packets. A PMSI is instantiated via one or more P-tunnels.
o C-S: A multicast source address, identifying a multicast source
located at a VPN customer site.
o C-G: A multicast group address used by a VPN customer.
o C-flow: A customer multicast flow. Each C-flow is identified by
the ordered pair (source address, group address), where each
address is in the customer's address space. The identifier of a
particular C-flow is usually written as (C-S,C-G).
Sets of C-flows can be identified by the use of the "C-*" wildcard
(see [RFC 6625]), e.g., (C-*,C-G).
o I-PMSI A-D Route: Inclusive PMSI Auto-Discovery route. Carried in
BGP Update messages, these routes are used to advertise the
default P-tunnel for a particular MVPN.
o S-PMSI A-D route: Selective PMSI Auto-Discovery route. Carried in
BGP Update messages, these routes are used to advertise the fact
that particular C-flows are bound to (i.e., are traveling through)
particular P-tunnels.
o x-PMSI A-D route: A route that is either an I-PMSI A-D route or an
S-PMSI A-D route.
o Leaf A-D route: A route that a multicast egress node sends in
order to join a particular P-tunnel.
Rosen, et al. Standards Track PAGE 4
RFC 8556 MVPN with BIER April 2018
o PMSI Tunnel attribute (PTA): In an x-PMSI A-D route, the Network
Layer Reachability Information (NLRI) of the route identifies a
PMSI. The BGP attribute known as the PMSI Tunnel attribute is
attached to such a route in order to identify a particular
P-tunnel that is associated with the PMSI. When C-flows of
multiple VPNs are carried in a single P-tunnel, this attribute
also carries the information needed to multiplex and demultiplex
the C-flows. A PTA can also be carried by a Leaf A-D root. In
this case, it contains information that is needed in order for the
originator of the route to join the specified P-tunnel.
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
BCP 14 [RFC 2119] [RFC 8174] when, and only when, they appear in all
capitals, as shown here.
2. Use of the PMSI Tunnel Attribute in x-PMSI A-D Routes
As defined in [RFC 6514], the PMSI Tunnel attribute (PTA) carried by
an x-PMSI A-D route identifies the P-tunnel that is used to
instantiate a particular PMSI. If a PMSI is to be instantiated by
BIER, the PTA is constructed by a BFIR.
If segmented P-tunnels are not being used, the PTA attached to a
given x-PMSI A-D route is constructed by the router that originated
the route (typically by the ingress Provider Edge (PE) router), and
the PTA is not changed as the route is propagated.
If segmented P-tunnels are being used, the PTA attached to a given
x-PMSI A-D route by the route's originator may be replaced at a
segmentation point (a BFER) by a PTA identifying the next segment of
the P-tunnel. If the next segment of the P-tunnel is instantiated by
BIER, the segmentation point serves as the BFIR for that next
segment.
In either case, a PTA is constructed by a BFIR as follows (see
Figure 1):
The PTA contains the following fields:
o Tunnel Type: IANA has assigned 0x0B as the tunnel type codepoint
for "BIER" in the "P-Multicast Service Interface Tunnel (PMSI
Tunnel) Tunnel Types" registry. This codepoint is used to
indicate that the PMSI is instantiated by BIER.
Although BIER does not actually create tunnels, the MVPN
procedures treat BIER as if it were a type of tunnel.
Rosen, et al. Standards Track PAGE 5
RFC 8556 MVPN with BIER April 2018
o Tunnel Identifier: When the tunnel type is BIER, this field
contains three subfields:
1. The first subfield is a single octet, containing a BIER
sub-domain-id (see [RFC 8279]). This indicates that packets
sent on the PMSI will be sent on the specified BIER
sub-domain. How that sub-domain is chosen is outside the
scope of this document.
2. The second subfield is a two-octet field containing the BFR-id
in the sub-domain identified in the first subfield of the
router that is constructing the PTA.
3. The third subfield is the BFR-prefix (see [RFC 8279]) of the
router (a BFIR) that is constructing the PTA. The BFR-prefix
will either be a /32 IPv4 address or a /128 IPv6 address.
Whether the address is IPv4 or IPv6 can be inferred from the
total length of the PTA.
The BFR-prefix need not be the same IP address that is carried
in any other field of the x-PMSI A-D route, even if the BFIR
is the originating router of the x-PMSI A-D route.
Failure to properly set the Tunnel Identifier field cannot be
detected by the protocol and will result in improper delivery of
the data packets sent on the PMSI.
o MPLS Label: This field MUST contain an upstream-assigned non-zero
MPLS label. It is assigned by the router (a BFIR) that constructs
the PTA. Constraints on the way in which a BFIR selects this
label are discussed in Section 2.1.
Failure to follow the constraints on label assignment cannot be
detected by the protocol and may result in improper handling of
data packets by the egress PE routers.
o Flags: When the tunnel type is BIER, two of the flags in the PTA
Flags field are meaningful. Details about the use of these flags
can be found in Section 2.2.
* Leaf Information Required per Flow (LIR-pF): This flag is
introduced in [RFC 8534]. A BFIR SHOULD NOT set this flag
UNLESS it knows that all the BFERs in the BIER domain (or at
least all the BFERs to which it needs to transmit) support this
flag. (How this is known is outside the scope of this
document.) Procedures for the use of this flag are given in
Section 2.2.2. Support for this flag is OPTIONAL.
Rosen, et al. Standards Track PAGE 6
RFC 8556 MVPN with BIER April 2018
* Leaf Information Required (LIR): see Section 2.2.1.
+---------------------------------+
| Flags (1 octet) |
+---------------------------------+
| Tunnel Type = 0x0B (1 octet) |
+---------------------------------+
| MPLS Label (3 octets) |
+---------------------------------+
| Sub-domain-id (1 octet) | <---
+---------------------------------+ |
| BFR-id (2 octets) | |-- Tunnel
+---------------------------------+ | Identifier
| BFR-prefix (4 or 16 octets) | <---
+---------------------------------+
Figure 1: PMSI Tunnel Attribute for BIER
If a PTA specifying tunnel type BIER is attached to an x-PMSI A-D
route, the route MUST NOT be distributed beyond the boundaries of a
BIER domain. That is, any routers that receive the route must be in
the same BIER domain as the originator of the route. If the
originator is in more than one BIER domain, the route must be
distributed only within the BIER domain in which the BFR-prefix in
the PTA uniquely identifies the originator. As with all MVPN routes,
distribution of these routes is controlled by the provisioning of
Route Targets (RTs). Thus, the requirement expressed in this
paragraph is really a requirement on the way the Route Targets are
provisioned.
2.1. MPLS Label
The MPLS Label carried in the PTA is an upstream-assigned label.
If two PTAs contain the same BFR-prefix in their respective Tunnel
Identifier fields, then the labels carried in those PTAs MUST come
from the same label space (see Section 7 of [RFC 5331]). An
implementation may choose to use this fact when setting up the tables
it uses to interpret the upstream-assigned labels.
Suppose that a BFIR attaches a PTA to each of two x-PMSI A-D routes,
and both PTAs specify a tunnel type of BIER.
o If the two routes do not carry the same set of RTs, then their
respective PTAs MUST contain different MPLS label values.
Rosen, et al. Standards Track PAGE 7
RFC 8556 MVPN with BIER April 2018
o If the two routes do not have the same Address Family Identifier
(AFI) value, then their respective PTAs MUST contain different
MPLS label values. This ensures that when an egress PE receives a
data packet with the given label, the egress PE can infer from the
label whether the payload is an IPv4 packet or an IPv6 packet.
o If the BFIR is an ingress PE supporting MVPN extranet ([RFC 7900])
functionality, and if the two routes originate from different VPN
Routing and Forwarding tables (VRFs) on this ingress PE, then the
respective PTAs of the two routes MUST contain different MPLS
label values.
o If the BFIR is an ingress PE supporting the "Extranet Separation"
feature of MVPN extranet (see Section 7.3 of [RFC 7900]), and if
one of the routes carries the "Extranet Separation" extended
community but the other does not, then the respective PTAs of the
two routes MUST contain different MPLS label values.
o If segmented P-tunnels are being used, then the respective PTAs of
the two routes MUST contain different MPLS label values whenever
the respective NLRIs of the two routes are not identical. The
MPLS label can then be used at the next segmentation point to
switch packets from one P-tunnel segment directly to the next,
without requiring the segmentation points to contain any other
multicast forwarding state. This is explained further below; see
also Section 4.
When segmented P-tunnels are being used, a segmentation point, call
it "B1", may receive an x-PMSI A-D route whose PTA specifies BIER
from within a given BIER domain. This means that BIER is being used
for the previous segment of a segmented P-tunnel. If the next
segment is also of type BIER, B1 will be the BFIR for the next
segment. That is, B1 is a BFER of one BIER domain (corresponding to
the previous segment) and a BFIR of another BIER domain
(corresponding to the next segment). B1 needs to replace the PTA of
the x-PMSI A-D route with a new PTA, specifying its own BFR-prefix
and specifying an upstream-assigned label assigned by B1 itself.
Suppose that B1 has received two x-PMSI A-D routes, R1 and R2, where:
o R1 and R2 each have a PTA specifying BIER.
o R1's PTA specifies BFR-prefix B2 and Label L2.
o R2's PTA specifies BFR-prefix B3 and Label L3.
Rosen, et al. Standards Track PAGE 8
RFC 8556 MVPN with BIER April 2018
Suppose B1 decides to propagate both R1 and R2, replacing each PTA
with a new PTA specifying BIER. Suppose these new PTAs specify
labels L4 and L5,respectively. Then L4 and L5 MUST be different
(upstream-assigned) label values, UNLESS both of the following
conditions hold:
o R1 and R2 have the same value in the Originating Router field of
their respective NLRIs, and
o B2 is equal to B3, and
o L2 is equal to L3.
The segmentation point (B1, in this example) MUST also program its
data plane appropriately. For example, when:
o B1 receives a BIER packet for which it is a BFER, and
o the BIER header specifies the BFIR-id that corresponds to B2, and
o the BIER payload is an MPLS packet with upstream-assigned label,
and
o the top label value is L2,
then the data plane must be programmed to replace L2 with L4 and to
re-encapsulate the packet in a BIER header with B1's BFR-id in the
BFIR-id field. The BitString of the new BIER header is determined by
applying the procedures for MVPN explicit tracking (see Section 2.2)
in the BIER domain of the next segment, i.e., in the BIER domain for
which B1 is the BFIR).
2.2. Explicit Tracking
When using BIER to transport an MVPN data packet through a BIER
domain, an ingress PE functions as a BFIR (see [RFC 8279]). The BFIR
must determine the set of BFERs to which the packet needs to be
delivered. This can be done in either of two ways:
1. Using the explicit tracking mechanism based on the "Leaf
Information Required" flag specified in [RFC 6513] and [RFC 6514].
This method is further described in Section 2.2.1.
2. Using the OPTIONAL explicit tracking mechanism based on the
LIR-pF flag specified in [RFC 8534]. This method, further
described in Section 2.2.2, may be used if (and only if)
segmented P-tunnels are not being used.
Rosen, et al. Standards Track PAGE 9
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2.2.1. Using the LIR Flag
To determine the set of BFERs to which the packets of a given C-flow
must be sent, a BFIR MUST originate a (C-S,C-G) S-PMSI A-D route for
the given C-flow. It MUST attach a PTA to that route and MUST set
the Leaf Information Required (LIR) flag in the PTA. Per [RFC 6514],
the BFERs that need to receive that C-flow will respond with
(C-S,C-G) Leaf A-D routes. By matching the received Leaf A-D routes
to the originated S-PMSI A-D routes, the originator of the S-PMSI A-D
route determines the set of BFERs that need to receive the multicast
data flow that is identified in the NLRI of S-PMSI A-D route.
Suppose that an ingress PE has originated an I-PMSI A-D route or a
wildcard S-PMSI A-D route [RFC 6625] with a PTA specifying a tunnel
type of BIER. Now suppose that the ingress PE originates an S-PMSI
A-D route specifying (C-S,C-G), where (C-S,C-G) "matches" (according
to the rules of [RFC 6625]) the wildcard S-PMSI A-D route or the
I-PMSI A-D route. Instead of attaching a PTA specifying BIER to the
(C-S,C-G) route, the ingress PE MAY attach a PTA specifying a tunnel
type of "no tunnel information". This is equivalent to attaching the
same PTA attached to the matching "less specific" route.
2.2.2. Using the LIR-pF Flag
If segmented P-tunnels are not being used, the BFIR can determine the
set of BFERs that need to receive the packets of a given (C-S,C-G)
C-flow as follows. The BFIR MUST originate a wildcard S-PMSI A-D
route (either (C-*,C-*), (C-*,C-G), or (C-S,C-G)), and the PTA of
that route MUST use the following settings:
o The LIR-pF flag MUST be set.
o The tunnel type MUST be set to BIER.
o A non-zero MPLS label MUST be specified.
Per [RFC 8534], a BFER that needs to receive (C-S,C-G) traffic from
the BFIR will respond with a Leaf A-D route.
A BFIR MUST NOT use this method of finding the set of BFERs needing
to receive a given C-flow unless it knows that all those BFERs
support the LIR-pF flag. How this is known is outside the scope of
this document.
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This method greatly reduces the number of S-PMSI A-D routes that a
BFIR needs to originate; it can now originate as few as one such
route (a (C-*,C-*) S-PMSI A-D route), rather than one for each
C-flow. However, the method does not provide a way for the BFIR to
assign a distinct label to each C-flow. Therefore, it cannot be used
when segmented P-tunnels are in use (see Section 4 for an
explanation).
Note: If a BFIR originates a (C-*,C-*) S-PMSI A-D route with the
LIR-pF flag set but also originates a more specific wildcard route
that matches a particular (C-S,C-G), the BFERs will not originate
Leaf A-D routes for that (C-S,C-G) unless the LIR-pF flag is also set
in the more specific wildcard route. If the BFIR also originates a
(C-S,C-G) S-PMSI A-D route without the LIR flag set, the BFERs will
not originate Leaf A-D routes for that (C-S,C-G) unless the LIR flag
is also set in that route.
3. Use of the PMSI Tunnel Attribute in Leaf A-D Routes
Before an egress PE can receive a (C-S,C-G) flow from a given ingress
PE via BIER, the egress PE must have received one of the following
x-PMSI A-D routes from the ingress PE:
o A (C-S,C-G) S-PMSI A-D route (i.e., an S-PMSI A-D route whose NLRI
encodes (C-S,C-G)) and whose PTA specifies a tunnel type of BIER.
If such a route is found, we refer to it as the "matching x-PMSI
A-D route."
o A "less specific" x-PMSI A-D route (one specifying (C-*,C-*),
(C-*,C-G), or (C-S,C-G)) whose PTA specifies a tunnel type of
BIER, and that is the egress PE's "match for reception" of
(C-S,C-G).
The rules for determining which x-PMSI A-D route is the match for
reception are given in [RFC 6625]. However, these rules are
modified here to exclude any x-PMSI A-D route that does not have a
PTA or whose PTA specifies "no tunnel type".
If such a route is found, we refer to it as the "matching x-PMSI
A-D route."
If no matching x-PMSI A-D route for (C-S,C-G) is found, the egress PE
cannot receive the (C-S,C-G) flow from the ingress PE via BIER until
such time as a matching route is received.
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When an egress PE determines that it needs to receive a (C-S,C-G)
flow from a particular ingress PE via BIER, it originates a Leaf A-D
route. Construction of the Leaf A-D route generally follows the
procedures specified in [RFC 6514] or, optionally, the procedures
specified in [RFC 8534]. However, when BIER is being used, the Leaf
A-D route MUST carry a PTA that is constructed as follows:
1. The tunnel type MUST be set to BIER.
2. The MPLS Label field SHOULD be set to zero.
3. The sub-domain-id subfield of the Tunnel Identifier field (as
defined in Section 2) MUST be set to the corresponding value from
the PTA of the matching x-PMSI A-D route.
4. The BFR-id subfield of the Tunnel Identifier field MUST be set to
the BFR-id in the sub-domain identified by the sub-domain-id
subfield of the egress PE (BFER).
5. The BFR-prefix field of the Tunnel Identifier field (as defined
in Section 2) MUST be set to the egress PE's (BFER's) BFR-prefix.
The BFR-prefix need not be the same IP address that is carried in
any other field of the Leaf A-D route.
When an ingress PE receives such a Leaf A-D route, it learns the
BFR-prefix of the egress PE from the PTA. The ingress PE does not
make any use the value of the PTA's MPLS label field.
Failure to properly construct the PTA cannot always be detected by
the protocol and will cause improper delivery of the data packets.
4. Data Plane
The MVPN application plays the role of the "multicast flow overlay"
as described in [RFC 8279].
4.1. Encapsulation and Transmission
To transmit an MVPN data packet, an ingress PE follows the rules of
[RFC 6625] to find the x-PMSI A-D route that is a "match for
transmission" for that packet. (In applying the rules of [RFC 6625],
any S-PMSI A-D route with a PTA specifying "no tunnel information" is
ignored.) If the matching route has a PTA specifying BIER, the
(upstream-assigned) MPLS label from that PTA is pushed on the
packet's label stack. Then the packet is encapsulated in a BIER
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RFC 8556 MVPN with BIER April 2018
header. That is, the ingress PE functions as a BFIR. The BIER
sub-domain used for transmitting the packet is specified in the PTA
of the above-mentioned x-PMSI A-D route.
In order to create the proper BIER header for a given packet, the
BFIR must know all the BFERs that need to receive that packet. It
determines this by finding all the Leaf A-D routes that correspond to
the S-PMSI A-D route that is the packet's match for transmission.
There are two different cases to consider:
1. The S-PMSI A-D route that is the match for transmission carries a
PTA that has the LIR flag set but does not have the LIR-pF flag
set.
In this case, the corresponding Leaf A-D routes are those whose
"route key" field is identical to the NLRI of the S-PMSI A-D
route.
2. The S-PMSI A-D route that is the match for transmission carries a
PTA that has the LIR-pF flag.
In this case, the corresponding Leaf A-D routes are those whose
"route key" field is derived from the NLRI of the S-PMSI A-D
route according to the procedures described in Section 5.2 of
[RFC 8534].
The Leaf A-D route from a given BFER will contain a PTA that
specifies the BFER's BFR-prefix. With this information, the BFIR can
construct the BIER BitString.
However, if the PTA of the Leaf A-D route from a given BFER specifies
a sub-domain other than the one being used for transmitting the
packet, the bit for that BFER cannot be determined and that BFER will
not receive the packet.
The BIER-encapsulated packet is then forwarded, according to the
procedures described in [RFC 8279] and [RFC 8296]. (See especially
Section 3, "Imposing and Processing the BIER Encapsulation" in
[RFC 8296].)
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RFC 8556 MVPN with BIER April 2018
4.2. Disposition
When a BFER receives an MVPN multicast data packet that has been
BIER-encapsulated, the BIER layer passes the following information to
the multicast flow overlay:
o The sub-domain-id and the BFIR-id from the BIER header. (As the
sub-domain-id is inferred from the BIFT-id field of the BIER
header, an implementation might choose to pass the BIFT-id rather
than the sub-domain-id; this is an implementation matter.)
o The "payload", which is an MPLS packet whose top label is an
upstream-assigned label. In the data plane, the BFIR-id and the
sub-domain-id provide the context in which the upstream-assigned
label is interpreted.
By looking up the upstream-assigned label in the appropriate context,
the multicast flow overlay determines whether the BFER is an egress
PE for the packet.
Note that if segmented P-tunnels are in use, a BFER might be a
P-tunnel segmentation border router rather than an egress PE, or a
BFER might be both an egress PE and a P-tunnel segmentation border
router. Depending upon the role of the BFER for the given packet, it
may need to follow the procedures of Section 4.2.1, the procedures of
Section 4.2.2, or both.
4.2.1. At a BFER That Is an Egress PE
From looking up the packet's upstream-assigned label in the context
of the packet's BFIR-prefix, the egress PE determines the egress VRF
for the packet. From the IP header of the payload, the multicast
states of the VRF, the upstream-assigned label, and the BFR-prefix,
the egress PE can determine whether the packet needs to be forwarded
out one or more VRF interfaces.
4.2.2. At a BFER That Is a P-tunnel Segmentation Boundary
When segmented P-tunnels are being used, a BFER that receives a BIER-
encapsulated MVPN multicast data packet may need to be forwarded on
its next P-tunnel segment. The choice of the next P-tunnel segment
for the packet depends upon the C-flow to which the packet belongs.
As long as the BFIR has assigned the MPLS label according to the
constraints specified in Section 2.1, the BFIR will have assigned
distinct upstream-assigned MPLS labels to distinct C-flows. The BFER
can thus select the proper "next P-tunnel segment" for a given packet
simply by looking up the upstream-assigned label that immediately
follows the BIER header.
Rosen, et al. Standards Track PAGE 14
RFC 8556 MVPN with BIER April 2018
5. IANA Considerations
IANA has assigned the codepoint 0x0B to BIER in the "P-Multicast
Service Interface Tunnel (PMSI Tunnel) Tunnel Types" registry.
6. Security Considerations
The procedures of this document do not, in themselves, provide
privacy, integrity, or authentication for the control plane or the
data plane. For a discussion of the security considerations
regarding the use of BIER, please see [RFC 8279] and [RFC 8296].
Security considerations regarding VPN technology based on [RFC 4364],
[RFC 6513], and [RFC 6514] can be found in those RFCs.
7. References
7.1. 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,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC 4364, February
2006, <https://www.rfc-editor.org/info/RFC 4364>.
[RFC 5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, DOI 10.17487/RFC 5331, August 2008,
<https://www.rfc-editor.org/info/RFC 5331>.
[RFC 6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC 6513, February
2012, <https://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,
<https://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,
<https://www.rfc-editor.org/info/RFC 6625>.
Rosen, et al. Standards Track PAGE 15
RFC 8556 MVPN with BIER April 2018
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[RFC 8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC 8279, November 2017,
<https://www.rfc-editor.org/info/RFC 8279>.
[RFC 8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC 8296, January
2018, <https://www.rfc-editor.org/info/RFC 8296>.
[RFC 8534] Dolganow, A., Kotalwar, J., Rosen, E., Ed., and Z. Zhang,
"Explicit Tracking with Wildcard Routes in Multicast VPN",
RFC 8534, DOI 10.17487/RFC 8534, February 2019,
<https://www.rfc-editor.org/info/RFC 8534>.
7.2. Informative References
[RFC 7524] Rekhter, Y., Rosen, E., Aggarwal, R., Morin, T.,
Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area
Point-to-Multipoint (P2MP) Segmented Label Switched Paths
(LSPs)", RFC 7524, DOI 10.17487/RFC 7524, May 2015,
<https://www.rfc-editor.org/info/RFC 7524>.
[RFC 7900] Rekhter, Y., Ed., Rosen, E., Ed., Aggarwal, R., Cai, Y.,
and T. Morin, "Extranet Multicast in BGP/IP MPLS VPNs",
RFC 7900, DOI 10.17487/RFC 7900, June 2016,
<https://www.rfc-editor.org/info/RFC 7900>.
Acknowledgments
The authors wish to thank Jeffrey Zhang for his ideas and
contributions to this work. We also thank Stig Venaas for his review
and comments.
Contributors
IJsbrand Wijnands
Cisco Systems, Inc.
De Kleetlaan 6a
Diegem 1831
Belgium
Email: ice@cisco.com
Rosen, et al. Standards Track PAGE 16
RFC 8556 MVPN with BIER April 2018
Authors' Addresses
Eric C. Rosen (editor)
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts 01886
United States of America
Email: erosen52@gmail.com
Mahesh Sivakumar
Juniper Networks, Inc.
1137 Innovation Way
Sunnyvale, California 94089
United States of America
Email: sivakumar.mahesh@gmail.com
Tony Przygienda
Juniper Networks, Inc.
1137 Innovation Way
Sunnyvale, California 94089
United States of America
Email: prz@juniper.net
Sam K Aldrin
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, California
United States of America
Email: aldrin.ietf@gmail.com
Andrew Dolganow
Nokia
438B Alexandra Rd #08-07/10
Alexandra Technopark
Singapore 119968
Email: andrew.dolganow@nokia.com
Rosen, et al. Standards Track PAGE 17
RFC TOTAL SIZE: 38070 bytes
PUBLICATION DATE: Monday, April 8th, 2019
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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