Network Working Group J. Dong
Internet-Draft H. Wang
Intended status: Standards Track Huawei Technologies
Expires: September 10, 2012 March 9, 2012
Pseudowire Redundancy on S-PE
draft-dong-pwe3-redundancy-spe-01
Abstract
This document describes Multi-Segment Pseudowire (MS-PW) protection
scenarios in which the pseudowire redundancy is provided on the
Switching-PE (S-PE). Signaling of preferential forwarding defined in
[I-D.ietf-pwe3-redundancy-bit] is reused.
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
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provisions of BCP 78 and BCP 79.
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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 . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
[I-D.ietf-pwe3-redundancy] and [I-D.ietf-pwe3-redundancy-bit]
describe Pseudowire (PW) redundancy mechanism for scenarios where a
set of redundant PWs terminate on either provider edge (PE) nodes in
single-segment pseudowire (SS-PW) [RFC3985]applications, or on
terminating provider edge (T-PE) nodes in multi-segment pseudowire
(MS-PW) [RFC5659] applications. This document describes the
scenarios where PW redundancy is provided on S-PEs of MS-PW.
Signaling of preferential forwarding defined in
[I-D.ietf-pwe3-redundancy-bit] is reused for these scenarios, and
operations on S-PE are specified.
2. PW Redundancy on S-PE
In some MS-PW deployment scenarios, PW redundancy may need to be
provided on S-PE. 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 scenario in Figure 1 since
on T-PE1 side it may be impossible to provide PW redundancy,
especially when the PW-Seg1 between T-PE1 and S-PE1 is statically
configured. For 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 PW redundancy. Also PW redundancy on
S-PE could provide faster protection switching than end-to-end
protection switching of MS-PW.
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+---+ +-----+ +-----+ +-----+
| | | | | | | |
| | |......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, 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 scenario in Figure 2 since
it reduces the number of end-to-end MS-PWs required for both T-PE and
S-PE protection. Also redundancy on S-PE could provide faster
protection switching than end-to-end protection switching of MS-PW.
3. S-PE Operations
When S-PE redundancy is provisioned, it is necessary that S-PE could
perform protection switching according to the status change of PW
segments and announce appropriate PW status to adjacent PEs.
Signaling of preferential forwarding defined in
[I-D.ietf-pwe3-redundancy-bit] is reused for these scenarios, and
operation on S-PE is specified as below.
For scenario of Figure 1, assume the AC from CE2 to T-PE2 is active.
if S-PE1 knows PW-Seg1 is in "PW forwarding" State, it would
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advertise "Preferential Forwarding" status bit of "Active" on both
PW-Seg2 and PW-Seg3. T-PE2 advertises the preferential status
"Active" and T-PE3 advertises the preferential status "Standby", by
matching the local and remote 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 would then advertise the
preferential status "Active" to S-PE1, and T-PE2 would advertise the
preferential status "Standby". S-PE1 would perform the switchover
according to the updated local and remote preferential forwarding
status, and select PW-Seg3 to forward traffic. If S-PE selects a new
Active PW segment successfully, it SHOULD NOT advertise any change of
the PW status to T-PE1. Hence T-PE1 would not be aware of the
failure on the remote side.
For scenario of Figure 2, assume the AC from CE2 to T-PE2 is active.
T-PE1 would advertise preferential status "Active" on PW1-Seg1 and
"Standby" on PW2-Seg1. According to the received preferential
status, S-PE1 SHOULD advertise preferential status "Active" on both
PW1-Seg2 and PW1-Seg3, and S-PE2 SHOULD advertise preferential status
"Standby" on both PW2-Seg2 and PW2-Seg3. T-PE2 advertises
preferential status "Active" on both PW1-Seg2 and PW2-Seg3, and T-PE3
advertises preferential status "Standby" on both PW1-Seg3 and PW2-
Seg3. By matching the local and remote preferential forwarding
status, PW1-Seg2 would be used for traffic forwarding. Since S-PE1
connects to the primary PW segment PW1-Seg2, it would advertise
preferential status "Active" to T-PE1. S-PE2 would advertise
preferential status "Standby" to T-PE1 since it does not connect to
the primary PW segment.
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 the
preferential status "Active" to S-PE1, and T-PE2 would advertise the
preferential status "Standby". S-PE1 would perform the switchover
according to the updated local and remote preferential forwarding
status, and select PW1-Seg3 to forward traffic. Since S-PE1 selects
a new Active PW segment successfully, it SHOULD NOT advertise any
change of the PW status to T-PE1, and T-PE would not be aware of the
failure on the remode side.
When the S-PE1 fails, T-PE1 would advertise the preferential status
"Active" to S-PE2, On receiving the change of preferential status,
S-PE2 SHOULD advertise the preferential status "Active" on both PW2-
Seg2 and PW2-Seg3. Then by matching the local and remote
preferential forwarding status, PW2-Seg2 would be selected as primary
PW segment, and traffic would be forwarded on MS-PW2.
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4. VCCV Considerations
PW VCCV [RFC5085] CC type 1 "PW ACH" can be used with S-PE redundancy
mechanism smoothly. If VCCV CC type 3 "TTL Expiry" is to be used,
the hop counts from T-PE1 to the remote T-PE needs be obtained in
advance. This can be achieved either by control plane SP-PE TLVs or
through data plane tracing of the MS-PW.
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 and Lizhong Jin for their
comments and suggestions.
8. References
8.1. Normative References
[I-D.ietf-pwe3-redundancy]
Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", draft-ietf-pwe3-redundancy-06 (work in
progress), February 2012.
[I-D.ietf-pwe3-redundancy-bit]
Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", draft-ietf-pwe3-redundancy-bit-06
(work in progress), February 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,
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October 2009.
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
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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