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IETF RFC 6515
Last modified on Monday, February 20th, 2012
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Internet Engineering Task Force (IETF) R. Aggarwal
Request for Comments: 6515 Juniper Networks, Inc.
Updates: 6514 E. Rosen
Category: Standard Track Cisco Systems, Inc.
ISSN: 2070-1721 February 2012
IPv4 and IPv6 Infrastructure Addresses in
BGP Updates for Multicast VPN
 Abstract
To provide Multicast VPN (MVPN) service, Provider Edge routers
originate BGP Update messages that carry Multicast-VPN ("MCAST-VPN")
BGP routes; they also originate unicast VPN routes that carry MVPN-
specific attributes. These routes encode addresses from the
customer's address space, as well as addresses from the provider's
address space. These two address spaces are independent, and the
address family (IPv4 or IPv6) of the two spaces may or may not be the
same. These routes always contain an "address family" field that
specifies whether the customer addresses are IPv4 addresses or
whether they are IPv6 addresses. However, there is no field that
explicitly specifies the address family of the provider addresses.
To ensure interoperability, this document specifies that provider
IPv4 addresses are always encoded in these update messages as 4-octet
addresses, and that the distinction between IPv4 and IPv6 is signaled
solely by the length of the address field. Specific cases are
explained in detail. This document updates RFC 6514.
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 5741.
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 6515.
Aggarwal & Rosen Standards Track PAGE 1 
RFC 6515 MVPN Infrastructure Addresses February 2012
Copyright Notice
Copyright (c) 2012 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 ....................................................2
1.1. IPv4 and IPv6 Addresses in MCAST-VPN Routes ................2
1.2. Specification of Requirements ..............................4
1.3. Acronyms Used in This Document .............................4
2. PE Addresses in MCAST-VPN Routes ................................4
3. VRF Route Import Extended Community .............................5
4. PMSI Tunnel Attributes in I-PMSI A-D Routes .....................6
4.1. Relationship to AFI Value ..................................6
4.2. Relationship to Next Hop Address Family ....................6
5. IANA Considerations .............................................7
6. Security Considerations .........................................7
7. Acknowledgments .................................................7
8. Normative References ............................................7
9. Informative References ..........................................7
1. Introduction
1.1. IPv4 and IPv6 Addresses in MCAST-VPN Routes
[MVPN-BGP] defines a new set of BGP route types that are used by
service providers (SPs) to provide Multicast Virtual Private Network
service to their customers. These routes have a newly defined BGP
NLRI, the "MCAST-VPN" NLRI. The MCAST-VPN NLRI is carried in the
NLRI field of the MP_REACH_NLRI/MP_UNREACH_NLRI attributes defined in
[BGP-MP]. The SAFI field of the MP_REACH_NLRI/MP_UNREACH_NLRI
attribute is used to identify the NLRI as being an MCAST-VPN NLRI.
Aggarwal & Rosen Standards Track PAGE 2
RFC 6515 MVPN Infrastructure Addresses February 2012
When the SAFI field of an MP_REACH_NLRI/MP_UNREACH_NLRI attribute has
the "MCAST-VPN" value, the AFI field has two defined values: 1 and 2.
AFI 1 indicates that any customer multicast addresses occurring in
the MP_REACH_NLRI/MP_UNREACH_NLRI attribute are IPv4 addresses; AFI 2
indicates that such addresses are IPv6 addresses.
However, some of the MCAST-VPN routes also contain addresses of
Provider Edge (PE) routers in the SP network. An SP with an IPv4
network may provide MVPN service for customers using IPv6, and an SP
with an IPv6 network may provide MVPN service for customers that use
IPv4. Therefore, the address family of the PE addresses MUST NOT be
inferred from the AFI field of the associated
MP_REACH_NLRI/MP_UNREACH_NLRI attribute.
The purpose of this document is to make clear that whenever a PE
address occurs in an MCAST-VPN route (whether in the NLRI or in an
attribute), the IP address family of that address is determined by
the length of the address (a length of 4 octets for IPv4 addresses, a
length of 16 octets for IPv6 addresses), NOT by the AFI field of the
route.
In particular, if a SP with an IPv4 core network is providing
MVPN/IPv6 service to a customer, the PE addresses in the MCAST-VPN
routes will be 4-octet IPv4 routes, even though the AFI of those
routes will have the value 2.
Some previous specifications (e.g., [RFC 4659] and [RFC 4798]) have
taken a different approach, requiring that in any routes containing
IPv6 or VPN-IPv6 customer addresses, the IPv4 PE addresses be
represented as IPv6-mapped IPv4 addresses [RFC 4291]. This document
does not use that approach. Rather, this specification uses the
approach adopted in [RFC 4684] and [RFC 5549]. The MCAST-VPN routes
contain enough information to enable the IP address family of the PE
addresses to be inferred from the address lengths.
[MVPN-BGP] also defines an attribute, the "VRF Route Import Extended
Community", that is attached to unicast VPN-IPv4 or VPN-IPv6 routes.
This extended community contains a PE address, and this document
specifies how to encode an IPv6 address in this attribute,
independent of whether the attribute is attached to a VPN-IPv4 route
or a VPN-IPv6 route.
This document also clarifies an issue with respect to the
significance of the Address Family field of an Intra-AS I-PMSI A-D
route that carries a PMSI Tunnel Attribute.
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RFC 6515 MVPN Infrastructure Addresses February 2012
1.2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].
1.3. Acronyms Used in This Document
This document uses a number of acronyms, mostly taken directly from
the BGP and VPN specifications.
- A-D Route: Auto-Discovery Route [MVPN]
- AFI: Address Family Identifier [BGP-MP]
- AS: Autonomous System [BGP]
- I-PMSI: Inclusive PMSI [RFC 4364]
- MVPN: Multicast Virtual Private Network [MVPN]
- MCAST-VPN routes: BGP routes of "MCAST-VPN" Subsequent Address
Family, as defined in [MVPN-BGP]. The NLRI of such routes may be
referred to as MCAST-VPN NLRI.
- MP_REACH_NLRI: Multiprotocol Reachable NLRI [BGP-MP]
- MP_UNREACH_NLRI: Multiprotocol Unreachable NLRI [BGP-MP]
- PMSI: Provider Multicast Service Interface [MVPN]
- NLRI: Network Layer Reachability Information [BGP]
- PE: Provider Edge [RFC 4364]
- S-PMSI: Selective PMSI [RFC 4364]
- SAFI: Subsequent Address Field Identifier [BGP-MP]
- SP: Service Provider
2. PE Addresses in MCAST-VPN Routes
PE addresses occur in MCAST-VPN routes in the following places:
1. "Network Address of Next Hop" field in the MP_REACH_NLRI
attribute, as defined in Section 3 of [BGP-MP]. This field is
preceded by a "length of next hop address" field. Hence, it is
Aggarwal & Rosen Standards Track PAGE 4
RFC 6515 MVPN Infrastructure Addresses February 2012
always clear whether the address is an IPv4 address (length is 4)
or an IPv6 address (length is 16). If the length of the next hop
address is neither 4 nor 16, the MP_REACH_NLRI attribute MUST be
considered to be "incorrect", and MUST be handled as specified in
Section 7 of [BGP-MP].
2. "Intra-AS I-PMSI A-D route", defined in Section 4.1 of [MVPN-BGP].
All MCAST-VPN routes begin with a 1-octet route type field,
followed by a 1-octet "NLRI length" field. In the Intra-AS I-PMSI
A-D route, the length is followed by an 8-octet Route
Distinguisher (RD), which is then followed by the "Originating
Router's IP Address" field. The length of this field (4 octets
for IPv4 or 16 octets for IPv6) can thus be inferred from the NLRI
length field (which will be either 12 or 24, respectively). If
the inferred length of the "Originating Router's IP Address" field
is neither 4 nor 16, the MP_REACH_NLRI attribute MUST be
considered to be "incorrect", and MUST be handled as specified in
Section 7 of [BGP-MP].
3. "S-PMSI A-D Route", defined in Section 4.3 of [MVPN-BGP]. In this
route, the "NLRI length" field is followed by an 8-octet RD, a
variable-length "multicast source" field, a variable-length
"multicast group" field, and an "Originating Router's IP Address"
field. The two variable-length fields have their own length
fields. From these two length fields and the NLRI length field,
one can compute the length of the "Originating Router's IP
Address" field, which again is either 4 for IPv4 or 16 for IPv6.
If the computed length of the "Originating Router's IP Address"
field is neither 4 nor 16, the MP_REACH_NLRI attribute MUST be
considered to be "incorrect", and MUST be handled as specified in
Section 7 of [BGP-MP].
4. "Leaf A-D Route", defined in Section 4.4 of [MVPN-BGP]. In this
route, the "NLRI length" field is following by a variable-length
"route key", which is followed by the "Originating Router's IP
Address" field. The Route Key has its own length field. From the
NLRI length and the route key length, one can compute the length
of the "Originating Router's IP Address" field. If the computed
length of the "Originating Router's IP Address" field is neither 4
nor 16, the MP_REACH_NLRI attribute MUST be considered to be
"incorrect", and MUST be handled as specified in Section 7 of
[BGP-MP].
3. VRF Route Import Extended Community
The "VRF Route Import Extended Community", specified in [MVPN-BGP],
is an attribute carried by unicast VPN-IPv4 or VPN-IPv6 routes. It
is an "IPv4 Address Specific Extended Community" of type "VRF Route
Aggarwal & Rosen Standards Track PAGE 5
RFC 6515 MVPN Infrastructure Addresses February 2012
Import"; hence, it can only carry an IPv4 address. To carry an IPv6
address, an "IPv6 Address Specific Extended Community" [RFC 5701], of
type "VRF Route Import", must be used. A code point for this type of
extended community has been allocated by IANA.
4. PMSI Tunnel Attributes in I-PMSI A-D Routes
When a PMSI Tunnel Attribute occurs in an I-PMSI A-D route originated
by a particular PE or Autonomous System Border Router (ASBR), it
identifies a tunnel that the PE/ASBR uses by default for carrying the
multicast traffic of a particular customer MVPN. The proper encoding
and interpretation of the PMSI Tunnel attribute is affected by both
the AFI and "Network Address of Next Hop" fields.
4.1. Relationship to AFI Value
When the PMSI Tunnel Attribute occurs in a BGP Update message with a
MP_REACH_NLRI attribute whose AFI is 1, the meaning is that the
identified tunnel is used by default to carry IPv4 MVPN traffic for a
particular customer MVPN. When the PMSI Tunnel Attribute occurs in a
BGP Update message with a MP_REACH_NLRI attribute whose AFI is 2, the
meaning is that the identified tunnel is used by default to carry
IPv6 MVPN traffic for a particular customer MVPN. To assign both
IPv4 and IPv6 MVPN traffic to an I-PMSI tunnel, two I-PMSI A-D routes
MUST be used -- one whose MP_REACH_NLRI has an AFI of 1 and one whose
MP_REACH_NLRI has an AFI of 2. To use the same tunnel for both IPv4
and IPv6 traffic, the same value of the PMSI Tunnel attribute can be
used in each route.
4.2. Relationship to Next Hop Address Family
If the "Network Address of Next Hop" field in the MP_REACH_NLRI
attribute contains an IPv4 address, then any IP addresses appearing
in the "Tunnel Identifier" field of the PMSI Tunnel Attribute MUST be
IPv4 addresses.
If the "Network Address of Next Hop" field in the MP_REACH_NLRI
attribute contains an IPv6 address, then any IP addresses appearing
in the "Tunnel Identifier" field of the PMSI Tunnel Attribute MUST be
IPv6 addresses.
If these conditions are not met, the PMSI Tunnel Attribute MUST be
handled as a "malformed" PMSI Tunnel Attribute, as specified in
Section 5 of [MVPN-BGP].
Aggarwal & Rosen Standards Track PAGE 6
RFC 6515 MVPN Infrastructure Addresses February 2012
5. IANA Considerations
IANA has assigned the code point 0x000b for "VRF Route Import" in the
"IPv6 Address Specific Extended Community" registry in the
"transitive communities" portion of the namespace. The references
are to this document and to [MVPN-BGP].
6. Security Considerations
This document does not raise any security considerations beyond those
raised by [MVPN-BGP].
7. Acknowledgments
The authors wish to thank Dongling Duan, Keyur Patel, Yakov Rekhter,
and Karthik Subramanian.
8. Normative References
[BGP] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, January
2006.
[BGP-MP] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760, January
2007.
[MVPN] Rosen, E., Ed., and R. Aggarwal, Ed., "Multicast in
MPLS/BGP IP VPNs", RFC 6513, February 2012.
[MVPN-BGP] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, February 2012.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9. Informative References
[RFC 4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC 4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC 4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
"BGP-MPLS IP Virtual Private Network (VPN) Extension for
IPv6 VPN", RFC 4659, September 2006.
Aggarwal & Rosen Standards Track PAGE 7
RFC 6515 MVPN Infrastructure Addresses February 2012
[RFC 4798] De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS Using IPv6
Provider Edge Routers (6PE)", RFC 4798, February 2007.
[RFC 4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, November 2006.
[RFC 5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
Layer Reachability Information with an IPv6 Next Hop", RFC
5549, May 2009.
[RFC 5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community
Attribute", RFC 5701, November 2009.
Authors' Addresses
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089
EMail: raggarwa_1@yahoo.com
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
EMail: erosen@cisco.com
Aggarwal & Rosen Standards Track PAGE 8
RFC TOTAL SIZE: 17550 bytes
PUBLICATION DATE: Monday, February 20th, 2012
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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