Internet DRAFT - draft-ietf-pwe3-redundancy-spe
draft-ietf-pwe3-redundancy-spe
Network Working Group J. Dong
Internet-Draft H. Wang
Intended status: Standards Track Huawei Technologies
Expires: May 14, 2015 November 10, 2014
Pseudowire Redundancy on S-PE
draft-ietf-pwe3-redundancy-spe-03
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 [RFC6870] 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on May 14, 2015.
Copyright Notice
Copyright (c) 2014 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
Dong & Wang Expires May 14, 2015 [Page 1]
Internet-Draft PW redundancy on S-PE November 2014
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Typical Scenarios of PW Redundancy on S-PE . . . . . . . . . 2
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 . . . . . . . . . . . . . . . . 5
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
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
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 [RFC6870] is reused. This document does not
require any change to the T-PEs of MS-PW.
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.
Dong & Wang Expires May 14, 2015 [Page 2]
Internet-Draft PW redundancy on S-PE November 2014
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 be able to provide PW
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 required between T-PE1 and S-PE1 is only half of the
number of PW segments needed when using end-to-end MS-PW redundancy.
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
Dong & Wang Expires May 14, 2015 [Page 3]
Internet-Draft PW redundancy on S-PE November 2014
+---+ +-----+ +-----+ +-----+
| | | | | | | |
| | |......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. 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.
Dong & Wang Expires May 14, 2015 [Page 4]
Internet-Draft PW redundancy on S-PE November 2014
In general, 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 Up/Down status and Preferential Forwarding status as
Up and Active SHOULD be selected for traffic forwarding.
The Signaling of Preferential Forwarding bit defined in [RFC6870] 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-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 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 status of
"Pseudowire forwarding", and select PW-Seg3 as the new PW Segment 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 status to T-PE1. S-PE1 may advertise the updated Switching
Point PE TLVs (SP-PE TLVs) [RFC6073] using 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
Dong & Wang Expires May 14, 2015 [Page 5]
Internet-Draft PW redundancy on S-PE November 2014
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 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 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 status of "Pseudowire
forwarding", 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. S-PE1 may
advertise the updated SP-PE TLVs [RFC6073] using Label Mapping
message to T-PE1.
If S-PE1 fails, T-PE1 would notice this through some kind of
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 kind of
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.
Dong & Wang Expires May 14, 2015 [Page 6]
Internet-Draft PW redundancy on S-PE November 2014
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 [RFC6870].
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, March 1997.
[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.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.
[RFC6870] Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", RFC 6870, February 2013.
8.2. Informative References
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[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.
Dong & Wang Expires May 14, 2015 [Page 7]
Internet-Draft PW redundancy on S-PE November 2014
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
Dong & Wang Expires May 14, 2015 [Page 8]
