Internet DRAFT - draft-dong-pwe3-redundancy-spe
draft-dong-pwe3-redundancy-spe
Network Working Group J. Dong
Internet-Draft H. Wang
Intended status: Standards Track Huawei Technologies
Expires: May 26, 2013 November 22, 2012
Pseudowire Redundancy on S-PE
draft-dong-pwe3-redundancy-spe-04
Abstract
This document describes Multi-Segment Pseudowire (MS-PW) protection
scenarios in which the pseudowire redundancy is provided on the
Switching-PE (S-PE). Operations of the S-PEs which provide PW
redundancy are specified. Signaling of the preferential forwarding
status as defined in [I-D.ietf-pwe3-redundancy-bit] is reused. This
document does not require any change to the T-PEs of MS-PW.
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].
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 May 26, 2013.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. PW Redundancy on S-PE . . . . . . . . . . . . . . . . . . . . . 3
3. S-PE Operations . . . . . . . . . . . . . . . . . . . . . . . . 4
4. VCCV Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
[RFC6718] describes the framework and requirements for pseudowire
(PW) redundancy, and [I-D.ietf-pwe3-redundancy-bit] specifies
Pseudowire (PW) redundancy mechanism for scenarios where a set of
redundant PWs is configured between provider edge (PE) nodes in
single-segment pseudowire (SS-PW) [RFC3985]applications, or between
terminating provider edge (T-PE) nodes in multi-segment pseudowire
(MS-PW) [RFC5659] applications.
In some MS-PW scenarios, there are some benefits to provide PW
redundancy on S-PEs, such as reducing the burden on the access T-PE
nodes, and faster protection switching. This document describes some
scenarios in which PW redundancy is provided on S-PEs, and specifies
the operations of the S-PEs. Signaling of the preferential
forwarding status as defined in [I-D.ietf-pwe3-redundancy-bit] is
reused. This document does not require any change to the T-PEs of
MS-PW.
2. PW Redundancy on S-PE
In some MS-PW deployment scenarios, there are some benefits to
provide PW redundancy on S-PEs. This section gives some examples of
PW redundancy on S-PE.
+-----+
+---+ +-----+ | | +---+
| | | |------|T-PE2|----| |
| | +-----+ | ..PW-Seg2.......| | |
| | |....PW-Seg1..... | +-----+ | |
|CE1|----|T-PE1|------|S-PE1| |CE2|
| | | | | . | +-----+ | |
| | +-----+ | ..PW-Seg3.......| | |
| | | |------|T-PE3|----| |
+---+ +-----+ | | +---+
+-----+
Figure 1.MS-PW Redundancy on S-PE
As illustrated in Figure 1, CE1 is connected to T-PE1 while CE2 is
dual-homed to T-PE2 and T-PE3. T-PE1 is connected to S-PE1 only, and
S-PE1 is connected to T-PE2 and T-PE3. The MS-PW is switched on
S-PE1, and PW-Seg2 and PW-Seg3 provides resiliency on S-PE1 for
failure of T-PE2 or T-PE3 or the connected ACs. PW-Seg2 is selected
as primary PW segment, and PW-Seg3 is secondary PW segment.
MS-PW redundancy on S-PE is beneficial for the scenario in Figure 1
since T-PE1 as an access node may not be able to provide PW
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redundancy, especially when the PW-Seg1 between T-PE1 and S-PE1 is
statically configured. And with PW redundancy on S-PE, the number of
PW segments needed between T-PE1 and S-PE1 is only half of the number
of PW segments needed for end-to-end MS-PW redundancy. In addition,
PW redundancy on S-PE could provide faster protection switching than
end-to-end protection switching of MS-PW.
+---+ +-----+ +-----+ +-----+
| | | | | | | |
| | |......PW1-Seg1......PW1-Seg2........|
| | | . | | |
|CE1|----|T-PE1|------|S-PE1|-----------|T-PE2|
| | | . | | . | PW1-Seg3 | | +---+
| | +---.-+ | ......... ......|----| |
| | |. | | . .| | | |
+---+ |. +-----+ . . +-----+ | |
|. . . |CE2|
|. .. | |
|. +-----+ . . +-----+ | |
|. | | . .| |----| |
|...PW2-Seg1.......... ......| +---+
| | . | PW2-Seg2 | |
----------|S-PE2|-----------|T-PE3|
| . | | |
| .....PW2-Seg3........|
| | | |
+-----+ +-----+
Figure 2. MS-PW Redundancy on S-PE with S-PE protection
As illustrated in Figure 2, CE1 is connected to T-PE1 while CE2 is
dual-homed to T-PE2 and T-PE3. T-PE1 is connected to S-PE1 and
S-PE2, and both S-PE1 and S-PE2 are connected to T-PE2 and T-PE3.
There are two MS-PWs which are switched at S-PE1 and S-PE2
respectively to provide S-PE node protection. For MS-PW1, the S-PE1
provides resiliency using PW1-Seg2 and PW1-Seg3. For MS-PW2, the
S-PE2 provides resiliency using PW2-Seg2 and PW2-Seg3. MS-PW1 is the
primary PW and PW1-Seg2 is the primary PW segment.
MS-PW redundancy on S-PE is beneficial for the scenario in Figure 2
since it reduces the number of end-to-end MS-PWs required for both
T-PE and S-PE protection. In addition, PW redundancy on S-PE could
provide faster protection switching than end-to-end protection
switching of MS-PW.
3. S-PE Operations
For an S-PE which provides PW redundancy, it is important to
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advertise proper preferential forwarding status to the PW segments on
both sides and perform protection switching according to the received
status. This section specifies the operations of S-PEs on which PW
redundancy is provisioned. This document does not make any change to
the T-PEs of MS-PW.
The S-PE SHOULD work as a Slave node for the single-connected side,
and SHOULD work in Independent mode for the multi-connected side.
The S-PE SHOULD pass the preferential forwarding status received from
the single-connected side unchanged to the PW segments on the multi-
connected side. The S-PE SHOULD advertise Standby status to the
single-connected side if it receives Standby status from all the PW
segments on the multi-connected side, and it SHOULD advertise Active
status to the single-connected side if it receives Active status from
any of the PW segments on the multi-connected side. For the single-
connected side, the active PW segment is determined by the T-PE on
this side, which works as the Master node. On the multi-connected
side, the PW segment which has both local and remote Preferential
Forwarding status as Active SHOULD be selected for traffic
forwarding.
The Signaling of Preferential Forwarding bit defined in
[I-D.ietf-pwe3-redundancy-bit] is reused in these scenarios.
For the scenario in Figure 1, assume the AC from CE2 to T-PE2 is
active. In normal operation, S-PE1 would receive Active Preferential
Forwarding status bit on the single-connected side from T-PE1, then
it would advertise Active Preferential Forwarding status bit on both
PW-Seg2 and PW-Seg3. T-PE2 and T-PE3 would advertise Active and
Standby preferential status bit respectively to S-PE1, reflecting the
forwarding state of the two ACs to CE2. By matching the local and
remote Up/Down status and Preferential Forwarding status, PW-Seg2
would be used for traffic forwarding.
On failure of the AC between CE2 and T-PE2, the forwarding state of
AC on T-PE3 is changed to Active. T-PE3 then advertises Active
Preferential Status to S-PE1, and T-PE2 would advertise the
Preferential Status bit of Standby to S-PE1. S-PE1 would perform the
switchover according to the updated local and remote Preferential
Forwarding status, and select PW-Seg3 for traffic forwarding. Since
S-PE1 still connects to an Active PW segment on the multi-connected
side, it will not advertise any change of the PW Preferential
Forwarding status to T-PE1. T-PE1 would not be aware of the
switchover on S-PE1.
For scenario of Figure 2, assume the AC from CE2 to T-PE2 is active.
T-PE1 works in Master mode and it would advertise Active and Standby
Preferential Forwarding status bit respectively to S-PE1 and S-PE2.
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According to the received Preferential Forwarding status bit, S-PE1
would advertise Active Preferential Forwarding status bit to both
T-PE2 and T-PE3, and S-PE2 would advertise Standby Preferential
Forwarding status bit to both T-PE2 and T-PE3. T-PE2 would advertise
Active Preferential Forwarding status bit to both S-PE1 and S-PE2,
and T-PE3 would advertise Standby Preferential Forwarding status bit
to both S-PE1 and S-PE2, reflecting the forwarding state of the two
ACs to CE2. By matching the local and remote Up/Down Status and
Preferential Forwarding status, PW1-Seg2 from S-PE1 to T-PE2 would be
used for traffic forwarding. Since S-PE1 connects to the Active PW
segment on the multi-connected side, it would advertise Active
Preferential Forwarding status bit to T-PE1, and S-PE2 would
advertise Standby Preferential Forwarding status bit to T-PE1 since
it does not have any Active PW segment on the multi-connected side.
On failure of the AC between CE2 and T-PE2, the forwarding state of
AC on T-PE3 is changed to Active. T-PE3 would then advertise Active
Preferential Forwarding status bit to both S-PE1 and S-PE2, and T-PE2
would advertise Standby Preferential Forwarding status bit to both
S-PE1 and S-PE2. S-PE1 would perform the switchover according to the
updated local and remote Preferential Forwarding status, and select
PW1-Seg3 for traffic forwarding. Since S-PE1 still has an Active PW
segment on the multi-connected side, it would not advertise any
change of the PW status to T-PE1. Thus T-PE1 would not be aware of
the switchover on S-PE1.
If S-PE1 fails, T-PE1 would notice this through some detection
mechanism and then advertise the Active Preferential Forwarding
status bit to S-PE2, and PW2-Seg1 would be selected by T-PE1 for
traffic forwarding. On receipt of the newly changed Preferential
Forwarding status, S-PE2 would advertise the Active Preferential
Forwarding status to both T-PE2 and T-PE3. T-PE2 and T-PE3 would
also notice the failure of S-PE1 by some detection mechanism. Then
by matching the local and remote Up/Down and Preferential Forwarding
status, PW2-Seg2 would be selected for traffic forwarding.
4. VCCV Considerations
PW VCCV [RFC5085] CC type 1 "PW ACH" can be used with S-PE redundancy
mechanism. VCCV CC type 2 "Router Alert Label" is not supported for
MS-PW as specified in [RFC6073]. If VCCV CC type 3 "TTL Expiry" is
to be used, the hop count from one T-PE to the remote T-PE needs to
be obtained in advance. This can be achieved either by control plane
SP-PE TLVs or through data plane tracing of the MS-PW.
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5. IANA Considerations
This document makes no request of IANA.
6. Security Considerations
This document has the same security properties as in the PWE3 control
protocol [RFC4447] and [I-D.ietf-pwe3-redundancy-bit].
7. Acknowledgements
The authors would like to thank Mach Chen, Lizhong Jin, Mustapha
Aissaoui, Luca Martini, Matthew Bocci and Stewart Bryant for their
comments and discussions.
8. References
8.1. Normative References
[I-D.ietf-pwe3-redundancy-bit]
Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", draft-ietf-pwe3-redundancy-bit-08
(work in progress), September 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
October 2009.
[RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", RFC 6718, August 2012.
8.2. Informative References
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
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Pseudowires", RFC 5085, December 2007.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.
Authors' Addresses
Jie Dong
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
Haibo Wang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing 100095
China
Email: rainsword.wang@huawei.com
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