One document matched: draft-morin-l3vpn-mvpn-fast-failover-00.txt
Network Working Group T. Morin
Internet-Draft France Telecom - Orange Labs
Intended status: Experimental Y. Rekhter
Expires: May 7, 2009 R. Aggarwal
Juniper Networks
W. Henderickx
P. Muley
Alcatel-Lucent
November 3, 2008
Multicast VPN fast upstream failover
draft-morin-l3vpn-mvpn-fast-failover-00
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 7, 2009.
Abstract
This document defines multicast VPN extensions and procedures that
allow fast failover for upstream failures, by allowing downstream PEs
to take into account the status of Provider-Tunnels (P-tunnels) when
selecting the upstream PE for a VPN multicast flow, and extending BGP
mVPN routing so that a C-multicast route can be advertised toward a
standby upstream PE.
Morin, et al. Expires May 7, 2009 [Page 1]
Internet-Draft mVPN fast upstream failover November 2008
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 RFC 2119 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. UMH Selection based on tunnel status . . . . . . . . . . . . . 3
3.1. Determining the status of a tunnel . . . . . . . . . . . . 4
3.1.1. mVPN tunnel root tracking . . . . . . . . . . . . . . 5
3.1.2. PE-P Upstream link status . . . . . . . . . . . . . . 5
3.1.3. P2MP RSVP-TE tunnels . . . . . . . . . . . . . . . . . 5
3.1.4. Leaf-initiated P-tunnels . . . . . . . . . . . . . . . 6
3.1.5. P2MP LSP OAM . . . . . . . . . . . . . . . . . . . . . 6
3.1.6. (S,G) counter information . . . . . . . . . . . . . . 6
4. Standby C-multicast route . . . . . . . . . . . . . . . . . . 7
4.1. Downstream PE behavior . . . . . . . . . . . . . . . . . . 7
4.2. Upstream PE behavior . . . . . . . . . . . . . . . . . . . 8
4.3. Reachability determination . . . . . . . . . . . . . . . . 9
5. Hot leaf standby . . . . . . . . . . . . . . . . . . . . . . . 9
6. Duplicate packets . . . . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 13
Morin, et al. Expires May 7, 2009 [Page 2]
Internet-Draft mVPN fast upstream failover November 2008
1. Introduction
In the context of multicast in BGP/MPLS VPNs, it is desirable to
provide mechanisms allowing fast recovery of connectivity on
different types of failures. This document addresses failures of
elements in the provider network that are upstream of PEs connected
to VPN sites with receivers.
The two first section describe two independent mechanisms, allowing
different levels of resiliency, and providing different failure
coverage:
o Section 3 describes local procedures allowing an egress PE (a PE
connected to a receiver site) to take into account the status of
P-Tunnels to determine the Upstream Multicast Hop (UMH) for a
given (C-S, C-G).
o Section 4 describes protocol extensions that can speed up failover
by not requiring any multicast VPN routing message exchange at
recovery time.
Moreover, section 5 describes a "hot leaf standby" mechanism, that
uses a combination of these two mechanisms.
2. Terminology
The terminology used in this document is the terminology defined in
[I-D.ietf-l3vpn-2547bis-mcast] and
[I-D.ietf-l3vpn-2547bis-mcast-bgp].
3. UMH Selection based on tunnel status
Current multicast VPN specifications [I-D.ietf-l3vpn-2547bis-mcast],
section 5.1, describe the procedures used by a multicast VPN
downstream PE to determine what the upstream multicast hop (UMH) is
for a said (C-S,C-G).
The procedure described here is an OPTIONAL procedure that consist in
having a downstream PE take into account the status of P-tunnels
rooted at each possible upstream PEs, for including or not including
each said PE in the list of candidate UMHs for a said (C-S,C-G)
state. The result is that, if a P-tunnel is "down" (see
Section 3.1), the PE that is the root of the P-Tunnel won't be
considered for UMH selection, which will result in the downstream PE
to failover to the upstream PE which is next in the list of
candidates.
Morin, et al. Expires May 7, 2009 [Page 3]
Internet-Draft mVPN fast upstream failover November 2008
More precisely, UMH determination for a said (C-S,C-G) will consider
the UMH candidates in the following order:
o first, the UMH candidates that advertise a PMSI bound to a tunnel
that is "up", and *if* the "allowed-SPMSI-only" configuration flag
is set (see below), the UMH candidates that do not advertise any
I- or S- PMSI applicable to the said (C-S,C-G)
o second, the UMH candidates that advertise a PMSI bound to a tunnel
that is "down" -- these will thus be used as a last resort to
ensure a graceful fallback to the basic mVPN UMH selection
procedures in the hypothetical case where a false negative would
occur when determining the status of all tunnels
The "allowed-SPMSI-only" configuration flag mentioned above is a
configuration flag that MUST be provided, that is necessary to allow
an upstream PE to use a policy where no I-PMSI is advertized for a
said VRF and where only S-PMSI are used, the S-PMSI advertisement
being possibly done only after the upstream PE receives a C-multicast
route for (C-S, C-G)/(C-*, C-G) to be carried over the advertised
S-PMSI.
For a said downstream PE and a said VRF, the P-tunnel corresponding
to a said upstream PE for a said (C-S,C-G) state is the S-PMSI tunnel
advertized by that upstream PE for this (C-S,C-G) and imported into
that VRF, or if there isn't any such S-PMSI, the I-PMSI tunnel
advertized by that PE and imported into that VRF.
3.1. Determining the status of a tunnel
Different factors can be considered to determine the "status" of a
P-tunnel and are described in the following sub-sections. The
procedure proposed here also allows that all downstream PEs don't
apply the same rules to define what the status of a P-tunnel is
(please see Section 6), and some of them will produce a result that
may be different for different downstream PEs. Thus what is called
the "status" of a P-tunnel in this section, is not a characteristic
of the tunnel in itself, but is the status of the tunnel, *as seen
from a particular downstream PE*.
Depending on the criteria used to determine the status of a P-tunnel,
there may be an interaction with other resiliency mechanism used for
the P-tunnel itself, and the UMH update may happen immediately or may
need to be delayed. Each particular case is covered in each separate
sub-section below.
Morin, et al. Expires May 7, 2009 [Page 4]
Internet-Draft mVPN fast upstream failover November 2008
3.1.1. mVPN tunnel root tracking
A condition to consider that the status of a P-tunnel is up is that
the root of the tunnel, as determined in the PMSI tunnel attribute,
is reachable through unicast routing tables. In this case the
downstream PE can immediately update its UMH when the reachability
condition changes.
This is similar to BGP next-hop tracking for VPNv4 routes, except
that the address considered is not the BGP next-hop address, but the
root address in the PMSI tunnel attribute.
If BGP next-hop tracking is done for VPNv4 routes, and the root
address of a said tunnel happens to be the same as the next-hop
address in the BGP autodiscovery route advertising the tunnel, then
this mechanisms may be omitted for this tunnel, as it will not bring
any specific benefit.
3.1.2. PE-P Upstream link status
A condition to consider a tunnel status as up can be that the last-
hop link of the P-tunnel is up.
In that case, if the PE can determine that there is no fast
restoration mechanism (such as MPLS FRR [RFC4090]) in place for the
P-tunnel, it can update the UMH immediately. Else, it should wait
before updating the UMH, to let the P-tunnel restoration mechanims
happen. A configurable timer MUST be provided for this purpose, and
it is recommended to provide a reasonable default value for this
timer.
3.1.3. P2MP RSVP-TE tunnels
For P-Tunnels of type P2MP MPLS-TE, the status of the P-Tunnel is
considered up if one or more of the P2MP RSVP-TE LSPs, identified by
the P-Tunnel Attribute, are in up state. The determination of
whether a P2MP RSVP-TE LSP is in up state requires Path and Resv
state for the LSP and is based on procedures in [RFC4875]. In this
case the downstream PE can immediately update its UMH when the
reachability condition changes.
When signaling state for a P2MP TE LSP is removed (e.g. if the
ingress of the P2MP TE LSP sends a PathTear message) or the P2MP TE
LSP changes state from up to down as determined by procedures in
[RFC4875], the status of the corresponding P-Tunnel SHOULD be re-
evaluated. If the P-Tunnel transitions from up to down state, the
upstream PE, that is the ingress of the P-Tunnel, SHOULD not be
considered a valid UMH.
Morin, et al. Expires May 7, 2009 [Page 5]
Internet-Draft mVPN fast upstream failover November 2008
3.1.4. Leaf-initiated P-tunnels
A PE can be removed from the UMH candidate list for a said (S,G) if
the P-tunnel for this S,G (I or S , depending) is leaf triggered
(PIM, mLDP), but for some reason internal to the protocol the
upstream one-hop branch of the tunnel from P to PE cannot be built.
In this case the downstream PE can immediately update its UMH when
the reachability condition changes.
3.1.5. P2MP LSP OAM
When a P2MP connectivity verification mechanism such as
[I-D.katz-ward-bfd-multipoint] used in conjunction with bootstraping
mechanisms described in [I-D.ietf-mpls-mcast-cv] has been setup for a
tunnel, the result of the connectivity verification can be used to
define the status of the tree.
If a MultipointHead session has been established on a P2MP MPLS LSP
so that BFD packets are periodically sent from the root toward
leaves, a condition to consider the status of corresponding tunnel as
up is that the BFD SessionState is Up.
When such a procedure is used, in context where fast restoration
mechanisms are used for the P-tunnels, downstream PEs should be
configured to wait before updating the UMH, to let the P-tunnel
restoration mechanims happen. A configurable timer MUST be provided
for this purpose, and it is recommended to provide a reasonable
default value for this timer.
3.1.6. (S,G) counter information
In cases, where the downstream node can be configured so that the
maximum inter-packet time is known for all the multicast flows mapped
on a P-tunnel, the local per-(C-S,C-G) traffic counter information
for traffic received on this P-tunnel can be used to determine the
status of the P-tunnel.
When such a procedure is used, in context where fast restoration
mechanisms are used for the P-tunnels, downstream PEs should be
configured to wait before updating the UMH, to let the P-tunnel
restoration mechanims happen. A configurable timer MUST be provided
for this purpose, and it is recommended to provide a reasonable
default value for this timer.
This method can be applicable for instance when a (S,G) flow is
mapped on an S-PMSI.
In cases where this mechanism is used in conjunction with Hot leaf
Morin, et al. Expires May 7, 2009 [Page 6]
Internet-Draft mVPN fast upstream failover November 2008
standby, then no prior knowledge of the rate of the multicast streams
is required ; downstream PEs can compare reception on the two
P-tunnels to determine when one of them is down.
4. Standby C-multicast route
The procedures described below are limited to the case where the site
that contains C-S is connected to exactly two PEs. The procedures
require all the PEs of that mVPN to follow the single forwarder PE
selection, as specified in [I-D.ietf-l3vpn-2547bis-mcast]. The
procedures assume that if a site of a given mVPN that contains C-S is
dual-homed to two PEs, then all then other sites of that mVPN would
have two VPN-IPv4 routes to C-S, each with its own RD.
As long as C-S is reachable via both PEs, a said downstream PE will
select one of the PEs connected to C-S as its Upstream PE with
respect to C-S. We will refer to the other PE connected to C-S as
the "Standby Upstream PE". Note that if the connectivity to C-S
through the Primary Upstream PE becomes unavailable, then the PE will
select the Standby Upstream PE as its Upstream PE with respect to
C-S.
For readability, in the following sub-sections, the procedures are
described for BGP C-multicast Source Tree Join routes, but they apply
equally to BGP C-multicast Shared Tree Join routes failover for the
case where the customer RP is dual-homed (substitute "C-RP" to
"C-S").
4.1. Downstream PE behavior
When a (downstream) PE connected to some site of an mVPN needs to
send a C-multicast route (C-S, C-G), then following the procedures
specified in Section "Originating C-multicast routes by a PE" of
[I-D.ietf-l3vpn-2547bis-mcast-bgp] the PE sends the C-multicast route
with RT that identifies the Upstream PE selected by the PE
originating the route. As long as C-S is reachable via the Primary
Upstream PE, the Upstream PE is the Primary Upstream PE. If C-S is
reachable only via the Standby Upstream PE, then the Upstream PE is
the Standby Upstream PE.
If C-S is reachable via both the Primary and the Standby Upstream PE,
then in addition to sending the C-multicast route with an RT that
identifies the Primary Upstream PE, the PE also originates and sends
a C-multicast route with an RT that identifies the Standby Upstream
PE. This route is formed so that it carries the semantic of being a
'standby' C-multicast route (to be completed in a further revision).
.
Morin, et al. Expires May 7, 2009 [Page 7]
Internet-Draft mVPN fast upstream failover November 2008
If at some later point the local PE determines that C-S is no longer
reachable through the Primary Upstream PE, the Standby Upstream PE
becomes the Upstream PE, and the local PE re-sends the C-multicast
route with RT that identifies the Standby Upstream PE, except that
now the route does not carry the Standby PE BGP Community (which
results in replacing the old route with a new route, with the only
difference between these routes being the presence/absence of the
Standby PE BGP Community).
4.2. Upstream PE behavior
When a PE receives a C-multicast route for a particular (C-S, C-G),
and the RT carried in the route results in importing the route into a
particular VRF on the PE, if the route carries the Standby PE BGP
Community, then the PE performs as follows:
when the PE determines that C-S is not reachable through some
other PE, the PE SHOULD install VRF PIM state corresponding to
this BGP C-multicast route (the result will be that a PIM Join
message will be sent to the CE towards C-S, and that the PE will
receive (C-S,C-G) traffic), and the PE SHOULD forward (C-S, C-G)
traffic received by the PE to other PEs through a P-tunnel rooted
at the PE.
Furthermore, irrespective of whether C-S carried in that route is
reachable through some other PE:
a) based on local policy, as soon as the PE receives this BGP
C-multicast route, the PE MAY install VRF PIM state corresponding
to this BGP Source Tree Join route (the result will be that Join
messages will be sent to the CE toward C-S, and that the PE will
receive (C-S,C-G) traffic)
b) based on local policy, as soon as the PE receives this BGP
C-multicast route, the PE MAY forward (C-S, C-G) traffic to other
PEs through a P-tunnel independently of the reachability of C-S
through some other PE. [note that this implies also doing (a)]
Doing neither (a), nor (b) for a said (C-S,C-G) is called "cold root
standby".
Doing (a) but not (b) for a said (C-S,C-G) is called "mild root
standby".
Doing (b) (which implies also doing (a)) for a said (C-S,C-G) is
called "hot root standby".
Morin, et al. Expires May 7, 2009 [Page 8]
Internet-Draft mVPN fast upstream failover November 2008
4.3. Reachability determination
The standby PE can use the following information to determine that
C-S can or cannot be reached through the primary PE:
o presence/absence of a VPNv4 route toward C-S
o supposing that the standby PE is an egress of the tunnel rooted at
the Primary PE, the standby PE can determine the reachability of
C-S through the Primary PE based on the status of this tunnel,
determined thanks to the same criteria as the ones described in
Section 3.1 (without using the UMH selection procedures of
Section 3)
o other mechanisms MAY be used
5. Hot leaf standby
The mechanisms defined in the two previous section can be used
together as follows.
The principle is that, for a said VRF (or possibly only for a said
C-S,C-G):
o downstream PEs advertise a Standby BGP C-multicast route (based on
Section 4)
o upstream PEs use the "hot standby" optional behavior and thus will
forward traffic for a said multicast state as soon as they have
whether a (primary) BGP C-multicast route or a Standby BGP
C-multicast route for that state (or both)
o downstream PEs accept traffic from the primary or standby tunnel,
based on the status of the tunnel (based on Section 3)
Other combinations of the mechanisms proposed in Section 4) and
Section 3 are for further study.
6. Duplicate packets
Multicast VPN specifications [I-D.ietf-l3vpn-2547bis-mcast] impose
that a PE only forwards to CEs the packets coming from the expected
usptream PE (Section 9.1).
We highlight the reader's attention to the fact that the respect of
this part of multicast VPN specifications is especially important
Morin, et al. Expires May 7, 2009 [Page 9]
Internet-Draft mVPN fast upstream failover November 2008
when two distinct upstream PEs are succeptible to forward the same
traffic on P-tunnels at the same time in steady state. This will be
the case when "hot root standby" mode is used (Section 4), and which
can also be the case if procedures of Section 3 are used and (a) the
rules determining the status of a tree are not the same on two
distinct downstream PEs or (b) the rule determining the status of a
tree depend on conditions local to a PE (e.g. the PE-P upstream link
being up).
7. IANA Considerations
Allocation is expected from IANA for the BGP "Standby PE" community.
(TBC)
[Note to RFC Editor: this section may be removed on publication as an
RFC.]
8. Security Considerations
9. Acknowledgements
TBC.
10. References
10.1. Normative References
[I-D.ietf-l3vpn-2547bis-mcast]
Aggarwal, R., Bandi, S., Cai, Y., Morin, T., Rekhter, Y.,
Rosen, E., Wijnands, I., and S. Yasukawa, "Multicast in
MPLS/BGP IP VPNs", draft-ietf-l3vpn-2547bis-mcast-07 (work
in progress), July 2008.
[I-D.ietf-l3vpn-2547bis-mcast-bgp]
Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", draft-ietf-l3vpn-2547bis-mcast-bgp-05 (work in
progress), June 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
"Extensions to Resource Reservation Protocol - Traffic
Morin, et al. Expires May 7, 2009 [Page 10]
Internet-Draft mVPN fast upstream failover November 2008
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
10.2. Informative References
[I-D.ietf-mpls-mcast-cv]
Swallow, G., "Connectivity Verification for Multicast
Label Switched Paths", draft-ietf-mpls-mcast-cv-00 (work
in progress), April 2007.
[I-D.katz-ward-bfd-multipoint]
Katz, D. and D. Ward, "BFD for Multipoint Networks",
draft-katz-ward-bfd-multipoint-01 (work in progress),
January 2008.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
Authors' Addresses
Thomas Morin
France Telecom - Orange Labs
2, avenue Pierre Marzin
Lannion 22307
France
Email: thomas.morin@orange-ftgroup.com
Yakov Rekhter
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
U.S.A.
Email: yakov@juniper.net
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
U.S.A.
Email: rahul@juniper.net
Morin, et al. Expires May 7, 2009 [Page 11]
Internet-Draft mVPN fast upstream failover November 2008
Wim Henderickx
Alcatel-Lucent
Copernicuslaan 50
Antwerp 2018
Belgium
Email: wim.henderickx@alcatel-lucent.com
Praveen Muley
Alcatel-Lucent
701 East Middlefield Rd
Mountain View, CA 94043
U.S.A.
Email: praveen.muley@alcatel-lucent.com
Morin, et al. Expires May 7, 2009 [Page 12]
Internet-Draft mVPN fast upstream failover November 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Morin, et al. Expires May 7, 2009 [Page 13]
| PAFTECH AB 2003-2026 | 2026-04-24 01:47:19 |