Network Working Group J. Dong
Internet-Draft H. Wang
Intended status: Standards Track Huawei Technologies
Expires: February 5, 2016 August 4, 2015
Pseudowire Redundancy on S-PE
draft-ietf-pals-redundancy-spe-02
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 in this document. Signaling of the
preferential forwarding status as defined in RFC 6870 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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on February 5, 2016.
Copyright Notice
Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Typical Scenarios of PW Redundancy on S-PE . . . . . . . . . 3
2.1. MS-PW Redundancy on S-PE . . . . . . . . . . . . . . . . 3
2.2. MS-PW Redundancy on S-PE with S-PE Protection . . . . . . 3
3. S-PE Operations . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Operations of Scenario 1 . . . . . . . . . . . . . . . . 5
3.2. Operations of Scenario 2 . . . . . . . . . . . . . . . . 6
4. VCCV Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[RFC6718] describes the framework and requirements for pseudowire
(PW) redundancy, and [RFC6870] 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 benefits to provide PW redundancy
on S-PEs, such as reducing the burden on the access T-PE nodes, and
enabling faster protection switching compared to the end-to-end MS-PW
protection mechanisms. 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 [RFC6870] is reused. This document does not
require any change to the T-PEs of MS-PW.
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2. Typical Scenarios of PW Redundancy on S-PE
In some MS-PW deployment scenarios, there are benefits to provide PW
redundancy on S-PEs. This section describes typical scenarios of PW
redundancy on S-PE.
2.1. MS-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 both 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 the primary PW segment, and PW-Seg3 is the 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 support PW redundancy.
Besides, with PW redundancy on S-PE, the number of PW segments
required between T-PE1 and S-PE1 is only half of the number of PW
segments needed when end-to-end MS-PW redundancy is used. In
addition, in this scenario PW redundancy on S-PE could provide faster
protection switching, compared with end-to-end protection switching
of MS-PW.
2.2. MS-PW Redundancy on S-PE with S-PE Protection
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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, and both S-PE1 and S-PE2 are connected to both 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, S-PE1
provides resiliency using PW1-Seg2 and PW1-Seg3. For MS-PW2, S-PE2
provides resiliency using PW2-Seg2 and PW2-Seg3. MS-PW1 is the
primary PW and PW1-Seg2 between S-PE1 and T-PE2 is the primary PW
segment. MS-PW2 is the secondary PW.
MS-PW redundancy on S-PE is beneficial for this scenario 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, compared with end-to-end protection
switching of MS-PW.
3. S-PE Operations
For an S-PE which provides PW redundancy for MS-PW, it is important
to advertise proper preferential forwarding status to the PW segments
on both sides and perform protection switching according to the
received status information. Note that when PW redundancy for MS-PW
is provided on S-PE, the optional S-PE Bypass Mode as defined in
[RFC6478] MUST NOT be used. This section specifies the operations of
S-PEs on which PW redundancy is provisioned. This section does not
make any change to the T-PEs of MS-PW.
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The S-PEs connect to the neighboring T-PEs or other S-PEs on two
sides with PW segments. For the S-PE which provides PW redundancy
for an MS-PW, on one side there is a single PW segment, which is
called the single-homed side, and on the other side there are
multiple PW segments, which is called the multi-homed side. The
scenario in which the S-PE has two multi-homed sides is out of scope.
In general, the S-PE MUST work as a Slave node for the single-homed
side, and MUST work in Independent mode for the multi-homed side.
Consequently, The T-PE on the single-homed side MUST work in the
Master mode, and the T-PEs on the multi-homed side MUST work in the
Independent mode. The S-PE MUST pass the preferential forwarding
status received from the single-homed side unchanged to the PW
segments on the multi-homed side. The S-PE MUST advertise Standby
status to the single-homed side if it receives Standby status from
all the PW segments on the multi-homed side, and it MUST advertise
Active status to the single-homed side if it receives Active status
from any of the PW segments on the multi-homed side. For the single-
homed side, the active PW segment is determined by the T-PE on this
side, which works as the Master node. On the multi-homed side, since
both the S-PE and T-PEs work in the Independent mode, the PW segment
which has both local and remote Up/Down status and Preferential
Forwarding status as Up and Active MUST be selected for traffic
forwarding.
The Signaling of Preferential Forwarding bit as defined in [RFC6870]
and [RFC6478] is reused in these scenarios.
3.1. Operations of Scenario 1
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-homed 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 to S-PE1 respectively, reflecting the
forwarding state of the two ACs connected 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 a PW status
Notification message to S-PE1, indicating that the AC between CE2 and
T-PE2 is down. S-PE1 would perform the switchover according to the
updated local and remote Preferential Forwarding status and the
status of "Pseudowire forwarding", and select PW-Seg3 as the new PW
Segment for traffic forwarding. Since S-PE1 still connects to an
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Active PW segment on the multi-homed side, it will not advertise any
change of the PW status to T-PE1. If S-PE1 supports the SP-PE TLV
processing as defined in [RFC6073], it SHOULD advertise the updated
SP-PE TLVs by sending a Label Mapping message to T-PE1.
3.2. Operations of Scenario 2
For the 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 according to configuration. 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 connected
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-homed 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-homed 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 a PW status Notification message to both S-PE1 and
S-PE2, indicating that the AC between CE2 and T-PE2 is down. S-PE1
would perform the switchover according to the updated local and
remote Preferential Forwarding status and the status of "Pseudowire
forwarding", and select PW1-Seg3 for traffic forwarding. Since S-PE1
still has an Active PW segment on the multi-homed side, it would not
advertise any change of the PW status to T-PE1. If S-PE1 supports
the SP-PE TLV processing as defined in [RFC6073], it SHOULD advertise
the updated SP-PE TLVs by sending a Label Mapping message to T-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.
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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 PW label TTL MUST be set to the appropriate value to
reach the target PE. The hop count from one T-PE to the target PE
can be obtained either via SP-PE TLVs, through MS-PW path trace or
based on management plane information.
5. IANA Considerations
This document makes no request of IANA.
6. Security Considerations
This document specifies the mechanisms of providing PW redundancy on
the S-PEs of MS-PWs. The security considerations specified in
[RFC4447], [RFC6073], [RFC6870] and [RFC6478] apply to this document.
7. Acknowledgements
The authors would like to thank Mach Chen, Lizhong Jin, Mustapha
Aissaoui, Luca Martini, Matthew Bocci and Stewart Bryant for their
valuable comments and discussions.
8. References
8.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
G. Heron, "Pseudowire Setup and Maintenance Using the
Label Distribution Protocol (LDP)", RFC 4447,
DOI 10.17487/RFC4447, April 2006,
<http://www.rfc-editor.org/info/rfc4447>.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073,
DOI 10.17487/RFC6073, January 2011,
<http://www.rfc-editor.org/info/rfc6073>.
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[RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci,
"Pseudowire Status for Static Pseudowires", RFC 6478,
DOI 10.17487/RFC6478, May 2012,
<http://www.rfc-editor.org/info/rfc6478>.
[RFC6870] Muley, P., Ed. and M. Aissaoui, Ed., "Pseudowire
Preferential Forwarding Status Bit", RFC 6870,
DOI 10.17487/RFC6870, February 2013,
<http://www.rfc-editor.org/info/rfc6870>.
8.2. Informative References
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<http://www.rfc-editor.org/info/rfc3985>.
[RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
Circuit Connectivity Verification (VCCV): A Control
Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
December 2007, <http://www.rfc-editor.org/info/rfc5085>.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
DOI 10.17487/RFC5659, October 2009,
<http://www.rfc-editor.org/info/rfc5659>.
[RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", RFC 6718, DOI 10.17487/RFC6718, August 2012,
<http://www.rfc-editor.org/info/rfc6718>.
Authors' Addresses
Jie Dong
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
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Haibo Wang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing 100095
China
Email: rainsword.wang@huawei.com
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