BESS Z. Zhang
Internet-Draft L. Giuliano
Updates: 6514 (if approved) Juniper Networks
Intended status: Standards Track May 19, 2021
Expires: November 20, 2021
MVPN and MSDP SA Interoperation
draft-ietf-bess-mvpn-msdp-sa-interoperation-07
Abstract
This document specifies the procedures for interoperation between
Multicast Virtual Private Network (MVPN) Source Active routes and
customer Multicast Source Discovery Protocol (MSDP) Source Active
routes, which is useful for MVPN provider networks offering services
to customers with an existing MSDP infrastructure. Without the
procedures described in this document, VPN-specific MSDP sessions are
required among the PEs that are customer MSDP peers. This document
updates RFC6514.
Requirements Language
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 20, 2021.
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Copyright Notice
Copyright (c) 2021 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
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described in the Simplified BSD License.
Table of Contents
1. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. MVPN RPT-SPT Mode . . . . . . . . . . . . . . . . . . . . 4
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Terminologies
Familiarity with MVPN and MSDP protocols and procedures is assumed.
Some terminologies are listed below for convenience.
o ASM: Any source multicast.
o SPT: Source-specific Shortest-path Tree.
o RPT: Rendezvous Point Tree.
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-RP: A multicast Rendezvous Point for a VPN customer.
o C-Multicast: Multicast for a VPN customer.
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o EC: Extended Community.
o GTM: Global Table Multicast, i.e., multicast in the default or
global routing table vs. VRF table.
2. Introduction
Section "14. Supporting PIM-SM without Inter-Site Shared C-Trees" of
[RFC6514] specifies the procedures for MVPN PEs to discover (C-S,C-G)
via MVPN Source Active A-D routes and then send (C-S,C-G) C-multicast
routes towards the ingress PEs, to establish SPTs for customer ASM
flows for which they have downstream receivers. (C-*,C-G)
C-multicast routes are not sent among the PEs so inter-site shared
C-Trees are not used and the method is generally referred to as "spt-
only" mode.
With this mode, the MVPN Source Active routes are functionally
similar to MSDP Source-Active messages [RFC3618]. For a VPN, one or
more of the PEs, say PE1, either act as a C-RP and learn of (C-S,C-G)
via PIM Register messages, or have MSDP sessions with some MSDP peers
and learn (C-S,C-G) via MSDP SA messages. In either case, PE1 will
then originate MVPN SA routes for other PEs to learn the (C-S,C-G).
[RFC6514] only specifies that a PE receiving the MVPN SA routes, say
PE2, will advertise (C-S,C-G) C-multicast routes if it has
corresponding (C-*,C-G) state learnt from its CE. PE2 may also have
MSDP sessions for the VPN with other C-RPs at its site, but [RFC6514]
does not specify that it advertises MSDP SA messages to those MSDP
peers for the (C-S,C-G) that it learns via MVPN SA routes. PE2 would
need to have an MSDP session with PE1 (that advertised the MVPN SA
messages) to learn the sources via MSDP SA messages, for it to
advertise the MSDP SA to its local peers. To make things worse,
unless blocked by policy control, PE2 would in turn advertise MVPN SA
routes because of those MSDP SA messages that it receives from PE1,
which are redundant and unnecessary. Also notice that the PE1-PE2
MSDP session is VPN-specific, while the BGP sessions over which the
MVPN routes are advertised are not.
If a PE does advertise MSDP SA messages based on received MVPN SA
routes, the VPN-specific MSDP sessions with other PEs are no longer
needed. Additionally, this MVPN/MSDP SA interoperation has the
following inherent benefits for a BGP based solution.
o MSDP SA refreshes are replaced with BGP hard state.
o Route Reflectors can be used instead of having peer-to-peer
sessions.
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o VPN extranet mechanisms can be used to propagate (C-S,C-G)
information across VPNs with flexible policy control.
While MSDP Source Active routes contain the source, group and RP
addresses of a given multicast flow, MVPN Source Active routes only
contain the source and group. MSDP requires the RP address
information in order to perform peer-RPF. Therefore, this document
describes how to convey the RP address information into the MVPN
Source Active route using an Extended Community so this information
can be shared with an existing MSDP infrastructure.
The procedures apply to Global Table Multicast (GTM) [RFC7716] as
well.
2.1. MVPN RPT-SPT Mode
For comparison, another method of supporting customer ASM is
generally referred to as "rpt-spt" mode. Section "13. Switching
from a Shared C-Tree to a Source C-Tree" of [RFC6514] specifies the
MVPN SA procedures for that mode, but those SA routes are a
replacement for PIM-ASM assert and (s,g,rpt) prune mechanisms, not
for source discovery purposes. MVPN/MSDP SA interoperation for the
"rpt-spt" mode is outside of the scope of this document. In the rest
of the document, the "spt-only" mode is assumed.
3. Specification
The MVPN PEs that act as customer RPs or have one or more MSDP
sessions in a VPN (or the global table in case of GTM) are treated as
an MSDP mesh group for that VPN (or the global table). In the rest
of the document, it is referred to as the PE mesh group. This PE
mesh group MUST NOT include other MSDP speakers, and is integrated
into the rest of MSDP infrastructure for the VPN (or the global
table) following normal MSDP rules and practices.
When an MVPN PE advertises an MVPN SA route following procedures in
[RFC6514] for the "spt-only" mode, it SHOULD attach an "MVPN SA RP-
address Extended Community". This is a Transitive IPv4-Address-
Specific Extended Community. The Local Administrative field is set
to zero and the Global Administrative field is set to an RP address
determined as the following:
o If the (C-S,C-G) is learnt as result of PIM Register mechanism,
the local RP address for the C-G is used.
o If the (C-S,C-G) is learnt as result of incoming MSDP SA messages,
the RP address in the selected MSDP SA message is used.
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In addition to procedures in [RFC6514], an MVPN PE may be provisioned
to generate MSDP SA messages from received MVPN SA routes, with or
without local policy control. If a received MVPN SA route triggers
an MSDP SA message, the MVPN SA route is treated as if a
corresponding MSDP SA message was received from within the PE mesh
group and normal MSDP procedure is followed (e.g. an MSDP SA message
is advertised to other MSDP peers outside the PE mesh group). The
(S,G) information comes from the (C-S,C-G) encoding in the MVPN SA
NLRI and the RP address comes from the "MVPN SA RP-address EC"
mentioned above. If the received MVPN SA route does not have the EC
(this could be from a legacy PE that does not have the capability to
attach the EC), the local RP address for the C-G is used. In that
case, it is possible that the receiving PE's RP for the C-G is
actually the MSDP peer to which the generated MSDP message is
advertised, causing the peer to discard it due to RPF failure. To
get around that problem the peer SHOULD use local policy to accept
the MSDP SA message.
An MVPN PE MAY treat only the best MVPN SA route selected by the BGP
route selection process (instead of all MVPN SA routes) for a given
(C-S,C-G) as a received MSDP SA message (and advertise the
corresponding MSDP message). In that case, if the selected best MVPN
SA route does not have the "MVPN SA RP-address EC" but another route
for the same (C-S, C-G) does, then the next best route with the EC
SHOULD be chosen. As a result, when/if the best MVPN SA route with
the EC changes, a new MSDP SA message is advertised if the RP address
determined according to the newly selected MVPN SA route is different
from before. The previously advertised MSDP SA message with the
older RP address will be timed out.
4. Security Considerations
RFC6514 specifies the procedure for a PE to generate an MVPN SA upon
discovering a (C-S,C-G) flow (e.g. via a received MSDP SA message) in
a VPN. This document extends this capability in the reverse
direction - upon receiving an MVPN SA route in a VPN generate
corresponding MSDP SA and advertise to MSDP peers in the same VPN.
As such, the capabilities specified in this document introduce no
additional security considerations beyond those already specified in
RFC6514 and RFC3618. Moreover, the capabilities specified in this
document actually eliminate the control message amplification that
exists today where VPN-specific MSDP sessions are required among the
PEs that are customer MSDP peers, which lead to redundant messages
(MSDP SAs and MVPN SAs) being carried in parallel between PEs.
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5. IANA Considerations
This document introduces a new Transitive IPv4 Address Specific
Extended Community "MVPN SA RP-address Extended Community". IANA has
registered subcode 0x20 in the Transitive IPv4-Address-Specific
Extended Community Sub-Types registry for this EC.
6. Acknowledgements
The authors thank Eric Rosen and Vinod Kumar for their review,
comments, questions and suggestions for this document. The authors
also thank Yajun Liu for her review and comments.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6514] 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/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[RFC3618] Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
Discovery Protocol (MSDP)", RFC 3618,
DOI 10.17487/RFC3618, October 2003,
<https://www.rfc-editor.org/info/rfc3618>.
[RFC7716] Zhang, J., Giuliano, L., Rosen, E., Ed., Subramanian, K.,
and D. Pacella, "Global Table Multicast with BGP Multicast
VPN (BGP-MVPN) Procedures", RFC 7716,
DOI 10.17487/RFC7716, December 2015,
<https://www.rfc-editor.org/info/rfc7716>.
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Authors' Addresses
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
Lenny Giuliano
Juniper Networks
EMail: lenny@juniper.net
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