Internet DRAFT - draft-zzhang-bess-mvpn-msdp-sa-interoperation
draft-zzhang-bess-mvpn-msdp-sa-interoperation
BESS Z. Zhang
Internet-Draft L. Giuliano
Updates: 6514 (if approved) Juniper Networks
Intended status: Standards Track January 18, 2018
Expires: July 22, 2018
MVPN and MSDP SA Interoperation
draft-zzhang-bess-mvpn-msdp-sa-interoperation-01
Abstract
This document specifies the procedures for interoperation between
MVPN Source Active routes and customer 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.
Requirements Language
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 RFC2119.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 22, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. MVPN RPT-SPT Mode . . . . . . . . . . . . . . . . . . . . 4
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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 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 EC: Extended Community.
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)
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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]. 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 with other C-RPs at its site, but [RFC6514] does not
specify that it advertise 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 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.
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
address 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.
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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 "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 replacement for
PIM-ASM assert and (s,g,rpt) prune mechanisms, not for source
discovery purpose. 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. It 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.
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 fine policy control. If a received MVPN SA route is to
trigger MSDP SA message, it 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
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local RP address for the C-G is used. In that case, it is possible
that 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 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 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 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. IANA Considerations
This document introduces a new Transitive IPv4 Address Specific
Extended Community "MVPN SA RP-address Extended Community". An IANA
request will be submitted for a subcode of 0x20 (pending approval and
subject to change) in the Transitive IPv4-Address-Specific Extended
Community Sub-Types registry.
5. 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.
6. References
6.1. 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>.
[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>.
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[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>.
6.2. Informative References
[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>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
Lenny Giuliano
Juniper Networks
EMail: lenny@juniper.net
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