Network Working Group A. Malis
Internet-Draft L. Andersson
Updates: 6870 (if approved) Huawei Technologies Co., Ltd
Intended status: Standards Track H. van Helvoort
Expires: April 13, 2015 Hai Gaoming BV
J. Shin
SK Telecom
L. Wang
China Mobile
A. D'Alessandro
Telecom Italia
October 10, 2014
S-PE Outage Protection for Static Multi-Segment Pseudowires
draft-shawam-pwe3-ms-pw-protection-02.txt
Abstract
In MPLS and MPLS-TP environments, statically provisioned Single-
Segment Pseudowires (SS-PWs) are protected against tunnel failure via
MPLS-level and MPLS-TP-level tunnel protection. With statically
provisioned Multi-Segment Pseudowires (MS-PWs), each segment of the
MS-PW is likewise protected from tunnel failures via MPLS-level and
MPLS-TP-level tunnel protection. However, static MS-PWs are not
protected end-to-end against failure of one of the switching PEs
(S-PEs) along the path of the MS-PW. This document describes how to
achieve this protection by updating the existing procedures in RFC
6870. It also contains an optional approach based on MPLS-TP Linear
Protection.
Status of This Memo
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This Internet-Draft will expire on April 13, 2015.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Extension to RFC 6870 to Protect Statically Provisioned SS-
PWs and MS-PWs . . . . . . . . . . . . . . . . . . . . . . . 3
3. Operational Considerations . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Optional Linear Protection Approach . . . . . . . . 6
A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 6
A.2. Encapsulation of the PSC Protocol for Pseudowires . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
As described in RFC 5659 [RFC5659], Multi-Segment Pseudowires (MS-
PWs) consist of terminating PEs (T-PEs), switching PEs (S-PEs), and
PW segments between the T-PEs at each of the MS-PW and the interior
S-PEs. In MPLS and MPLS-TP environments, statically provisioned
Single-Segment Pseudowires (SS-PWs) are protected against tunnel
failure via MPLS-level and MPLS-TP-level tunnel protection. With
statically provisioned Multi-Segment Pseudowires (MS-PWs), each PW
segment of the MS-PW is likewise protected from tunnel failure via
MPLS-level and MPLS-TP-level tunnel protection. However, PSN tunnel
protection does not protect static MS-PWs from failures of S-PEs
along the path of the MS-PW.
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RFC 6718 [RFC6718] provides a general framework for PW protection,
and RFC 6870 [RFC6870], which is based upon that framework, describes
protection procedures for MS-PWs that are dynamically signaled using
LDP. This document describes how to achieve protection against S-PE
failure in a static MS-PW by extending RFC 6870 to be applicable for
statically provisioned MS-PWs pseudowires (PWs) as well.
This document also contains an optional alternative approach based on
MPLS-TP Linear Protection. This approach, described in Appendix A,
MUST be identically provisioned in the PE endpoints for the protected
MS-PW in order to be used. See Appendix A for further details on
this alternative approach.
1.1. 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].
2. Extension to RFC 6870 to Protect Statically Provisioned SS-PWs and
MS-PWs
Section 3.2.3 of RFC 6718 and Section A.5 of RFC 6870 document how to
use redundant MS-PWs to protect an MS-PW against S-PE failure in the
case of a singly-homed CE, using the following network model from RFC
6718:
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Native |<----------- Pseudowires ----------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|.PW1-Seg2......|-------| |
| CE1| | |=========| |=========| | | CE2|
| | +-----+ +-----+ +-----+ | |
+----+ |.||.| |.||.| +----+
|.||.| +-----+ |.||.|
|.||.|=========| |========== .||.|
|.||...PW2-Seg1......|.PW2-Seg2...||.|
|.| ===========|S-PE2|============ |.|
|.| +-----+ |.|
|.|============+-----+============= .|
|.....PW3-Seg1.| | PW3-Seg2......|
==============|S-PE3|===============
| |
+-----+
Figure 1: Single-Homed CE with Redundant MS-PWs
In this figure, CE1 is connected to PE1 and CE2 is connected to PE2.
There are three MS PWs. PW1 is switched at S-PE1, PW2 is switched at
S-PE2, and PW3 is switched at S-PE3. This scenario provides N:1
protection against S-PE failure for the subset of the path of the
emulated service from T-PE1 to T-PE2.
The procedures in RFCs 6718 and 6870 rely on LDP-based PW status
signaling to signal the state of the primary MS-PW that is being
protected, and the precedence in which redundant MS-PW(s) should be
used to protect the primary MS-PW should it fail. These procedures
make use of information carried by the PW Status TLV, which for
dynamically signaled PWs is carried by the LDP protocol.
However, statically provisioned PWs (SS-PWs or MS-PWs) do not use the
LDP protocol for PW set and signaling, rather they are provisioned by
network management systems or other means at each T-PE and S-PE along
their path. They also do not use the LDP protocol for status
signaling. Rather, they use procedures defined in RFC 6478 [RFC6478]
for status signaling via the PW OAM message using the PW Associated
Channel Header (ACH). The PW Status TLV carried via this status
signaling is itself identical to the PW Status TLV carried via LDP-
based status signaling, including the identical PW Status Codes.
Sections 6 and 7 of RFC 6870 describes the management of a primary PW
and its secondary PW(s) to provide resiliency to the failure of the
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primary PW. They use status codes transmitted between endpoint T-PEs
using the PW Status TLV transmitted by LDP. For this management to
apply to statically provisioned PWs, the PW status signaling defined
in RFC 6478 MUST be used for the primary and secondary PWs. In that
case, the endpoint T-PEs can then use the PW status signaling
provided by RFC 6478 in the place of LDP-based status signaling, but
otherwise operate identically as described in RFC 6870.
3. Operational Considerations
Because LDP is not used between the T-PEs for statically provisioned
MS-PWs, the negotiation procedures described in RFC 6870 cannot be
used. Thus, operational care must be taken so that the endpoint
T-PEs are identically provisioned regarding the use of this document,
specifically whether or not MS-PW redundancy is being used, and for
each protected MS-PW, the identity of the primary MS-PW and the
precedence of the secondary MS-PWs.
4. Security Considerations
The security considerations defined for RFC 6478 apply to this
document as well. As the security considerations in RFCs 6718 and
6870 are related to their use of LDP, they are not required for this
document.
If the alternative approach in Appendix A is used, then the security
considerations defined for RFCs 6378, 7271, and 7324 also apply.
5. IANA Considerations
There are no requests for IANA actions in this document.
Note to the RFC Editor - this section can be removed before
publication.
6. Acknowledgements
The authors would like to thank Matthew Bocci, Yaakov Stein, and
David Sinicrope for their comments on this document.
Figure 1 and the explanatory paragraph following the figure were
taken from RFC 6718.
7. References
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7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
Protection", RFC 6378, October 2011.
[RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci,
"Pseudowire Status for Static Pseudowires", RFC 6478, May
2012.
[RFC6870] Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", RFC 6870, February 2013.
[RFC7271] Ryoo, J., Gray, E., van Helvoort, H., D'Alessandro, A.,
Cheung, T., and E. Osborne, "MPLS Transport Profile (MPLS-
TP) Linear Protection to Match the Operational
Expectations of Synchronous Digital Hierarchy, Optical
Transport Network, and Ethernet Transport Network
Operators", RFC 7271, June 2014.
[RFC7324] Osborne, E., "Updates to MPLS Transport Profile Linear
Protection", RFC 7324, July 2014.
7.2. Informative References
[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.
Appendix A. Optional Linear Protection Approach
A.1. Introduction
In "MPLS Transport Profile (MPLS-TP) Linear Protection" [RFC6378], as
well as in the later updates of this RFC in "MPLS Transport Profile
(MPLS-TP) Linear Protection to Match the Operational Expectations of
SDH, OTN and Ethernet Transport Network Operators" [RFC7271] and in
"Updates to MPLS Transport Profile Linear Protection" [RFC7324], the
Protection State Coordination (PSC) protocol was defined for MPLS
LSPs only.
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This Appendix extends these RFCs to be applicable for PWs (SS-PW and
MS-PW) as well. This is useful especially in the case of end-to-end
static provisioned MS-PWs running over MPLS-TP where tunnel
protection alone cannot be relied upon for end-to-end protection of
PWs against S-PE failure. It also enables a uniform operational
approach for protection at LSP and PW layers and an easier management
integration for networks that already use RFCs 6378, 7271, and 7324.
This Appendix is optional alternative approach to the one in
Section 2, therefore all implementations MUST include the approach in
Section 2 even if this alternative approach is used. The operational
considerations in Section 3 continue to apply when this approach is
used, and operational care must be taken so that the endpoint T-PEs
are identically provisioned regarding the use of this document.
A.2. Encapsulation of the PSC Protocol for Pseudowires
The PSC protocol can be used to protect against defects on any LSP
(segment, link or path). In the case of MS-PW, the PSC protocol can
also protect failed intermediate nodes (S-PE). Linear protection
protects an LSP or PW end-to-end and if a failure is detected,
switches traffic over to another (redundant) set of resources.
Obviously, the protected entity does not need to be of the same type
as the protecting. For example, it is possible to protect a link by
a path. Likewise it is possible to protect a SS-PW with a MS-PW and
vice versa.
From a PSC protocol point of view it is possible to view a SS-PW as a
single hop LSP, and a MS-PW as a multiple hop LSP. Thus, this
provides end-to-end protection for the SS-PW or MS-PW. The G-ACh
carrying the PSC protocol information is placed in the label stack
directly beneath the PW identifier. The PSC protocol will then work
as specified in RFCs 6378, 7271, and 7324.
Authors' Addresses
Andrew G. Malis
Huawei Technologies Co., Ltd
Email: agmalis@gmail.com
Loa Andersson
Huawei Technologies Co., Ltd
Email: loa@mail01.huawei.com
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Huub van Helvoort
Hai Gaoming BV
Email: huubatwork@gmail.com
Jongyoon Shin
SK Telecom
Email: jongyoon.shin@sk.com
Lei Wang
China Mobile
Email: wangleiyj@chinamobile.com
Alessandro D'Alessandro
Telecom Italia
Email: alessandro.dalessandro@telecomitalia.it
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