Internet DRAFT - draft-zzhang-bess-bgp-mvpn-source-active-route
draft-zzhang-bess-bgp-mvpn-source-active-route
bess Z. Zhang
Internet-Draft Juniper Networks
Updates: 6514 (if approved) R. Parekh
Intended status: Standards Track Cisco
Expires: 1 September 2024 29 February 2024
BGP-MVPN Source Active Route Enhancement
draft-zzhang-bess-bgp-mvpn-source-active-route-00
Abstract
RFC6514 specifies the protocol and procedures for multicast in MPLS/
BGP IP VPNs. In the Any-Source Multicast (ASM) case, the section
"14. Supporting PIM-SM without Inter-Site Shared C-Trees" specifies
that the Provider Edge that serves as a customer Rendezvous Point or
runs Multicast Source Discovery Protocol advertises Source Active
(SA) routes for ASM flows when it discovers those flows. This
document describes a situation where an optional enhancement to the
advertisement of SA routes is desired and specifies the procedures.
It updates RFC6514.
Status of This Memo
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This Internet-Draft will expire on 1 September 2024.
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Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
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Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. Normative References . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Background
Section "14. Supporting PIM-SM without Inter-Site Shared C-Trees" of
[RFC6514] specifies one way of supporting Any-Source Multicast (ASM)
for Multicast Virtual Private VPN (MVPN), referred to as SPT-only
mode in this document.
Consider the following topology:
source
|
CE1
|
PE1-------PE2 (c-rp)
\ /
\ /
PE3
|
CE3
|
receiver
When a receiver connected to the Last Hop Router (LHR) CE3 joins an
ASM group, CE3 sends a (*, G) Protocol Independent Multicast (PIM)
[RFC7611] Join Messages to PE3, which is the upstream router towards
the Customer-Rendezvous-Point (C-RP) on PE2. PE3 does not originate
a (C-*, C-G) C-Multicast BGP route (an equivalent of the PIM (*, G)
join message). Rather, it only originates (C-S, C-G) C-multicast BGP
routes (equivalent of PIM (S, G) join messages) when different
sources for the group G are discovered.
When the source starts sending multicast traffic for the ASM group G,
the First Hop Router (FHR) CE1 sends a PIM Register message to the
C-RP. PE2 then originates a (C-S, C-G) Source Active (SA) BGP route
to be imported by all PEs for the VPN. As a result, PE3 originates a
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(C-S, C-G) C-multicast route targeted at PE1 - the Upstream Multicast
Hop (UMH) for the C-S. PE1 then sends a corresponding (S, G) PIM
join message towards CE1.
[RFC6514] specifies the following situations where a PE originates SA
routes:
"A PE can obtain information about active multicast sources within a
given MVPN in a variety of ways. One way is for the PE to act as a
fully functional customer RP (C-RP) for that MVPN. Another way is to
use PIM Anycast RP procedures [PIM-ANYCAST-RP] to convey information
about active multicast sources from one or more of the MVPN C-RPs to
the PE. Yet another way is to use MSDP [MSDP] to convey information
about active multicast sources from the MVPN C-RPs to the PE."
In the above example, only PE2 will originate the SA routes. After
the signaling is done and traffic starts flowing, the LHR CE3 has the
option of sending a PIM (S, G) join message but it may choose not to.
If PE3 does not have the (S, G) join from CE3, and the SA route from
PE2 is withdrawn/invalidated for whatever reason (e.g. the BGP
session with PE2 goes down), PE3 will withdraw its (C-S, C-G)
C-Multicast route and PE1 will stop sending traffic. This
PE2-related failure should not have caused traffic loss since it is
not in the path at all.
This can be avoided if PE1 also originates the (C-S, C-G) SA route
when it receives the (C-S, C-G) C-multicast route. When PE1 does not
receive the (C-S, C-G) traffic for a while, it withdraws its
corresponding SA route, even though it still has the (C-S, C-G)
C-multicast route (otherwise the SA route and C-multicast route will
stay forever).
As long as there is any (C-S, C-G) SA route from any PE, PE3 will
originate its (C-S, C-G) C-Multicast Route targeting at the UMH PE of
its own choice. In the above example, while PE2 first originates the
SA route, PE3 still targets its C-Multicast route at PE1. When PE2's
SA route is invalidated/withdrawn, PE3 will keep its (C-S, C-G)
C-Multicast route if the SA route from PE1 is present.
2. Specification
This section specifies an optional enhancement to the origination of
SA routes in the SPT-only mode for supporting ASM.
Any PE that discovers a (C-S, C-G) flow on its PE-CE interfaces MUST
originate a corresponding (C-S, C-G) SA route, and MUST withdraw the
route when the flow is deemed no longer active.
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Besides the methods of discovering a flow described in the section 14
of [RFC6514] (as quoted earlier), a PE MAY use the its (C-S, C-G)
state for this purpose if the Reverse Path Forwarding (RPF) interface
is a PE-CE interface. The state may have been triggered by the
arrival of traffic on the PE-CE interface or by a corresponding (C-S,
C-G) C-Multicast route. when the (C-S, C-G) state is first created,
the PE MAY immediately originate a corresponding Source Active route
without waiting for the arrival of the traffic. When it stops
receiving traffic for over the PIM Keepalive_Period [RFC7761] or if
the (C-S, C-G) state is deleted, it MUST withdraws the SA route.
Note that while the Keepalive_Period value is used here, it does not
require the Keepalive Timer mechanism in [RFC7761].
3. Security Considerations
This document does not introduce any security issues.
4. Normative References
[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>.
[RFC7611] Uttaro, J., Mohapatra, P., Smith, D., Raszuk, R., and J.
Scudder, "BGP ACCEPT_OWN Community Attribute", RFC 7611,
DOI 10.17487/RFC7611, August 2015,
<https://www.rfc-editor.org/info/rfc7611>.
[RFC7761] 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/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
Rishabh Parekh
Cisco
Email: riparekh@cisco.com
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