Network Working Group W. Cheng
Internet-Draft L. Wang
Intended status: Informational H. Li
Expires: October 28, 2017 China Mobile
S. Davari
Broadcom Corporation
J. Dong
Huawei Technologies
April 26, 2017
Dual-Homing Protection for MPLS and MPLS-TP Pseudowires
draft-ietf-pals-mpls-tp-dual-homing-protection-06
Abstract
This document describes a framework and several scenarios for a
Pseudowire (PW) dual-homing local protection mechanism which avoids
unnecessary switchovers and which can be used for scenarios using a
control plane or not using a control plane. A Dual-Node
Interconnection (DNI) PW is used for carrying traffic between the
dual-homing Provider Edge (PE) nodes for carrying traffic when a
failure occurs in one of the Attachment Circuits (AC) or PWs. This
PW dual-homing local protection mechanism is complementary to
existing PW protection mechanisms.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 28, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Reference Models of Dual-homing Local Protection . . . . . . 3
2.1. PE Architecture . . . . . . . . . . . . . . . . . . . . . 3
2.2. Dual-Homing Local Protection Reference Scenarios . . . . 4
2.2.1. One-Side Dual-Homing Protection . . . . . . . . . . . 4
2.2.2. Two-side Dual-Homing Protection . . . . . . . . . . . 6
3. Generic Dual-homing PW Protection Mechanism . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[RFC6372] and [RFC6378] describe the framework and mechanism of MPLS-
TP Linear protection, which can provide protection for the MPLS LSP
or pseudowire (PW) between the edge nodes. This mechanism does not
protect the failure of the Attachment Circuit (AC) or the Provider
Edge (PE) node. [RFC6718] and [RFC6870] describe the framework and
mechanism for PW redundancy to provide protection for AC or PE node
failure. The PW redundancy mechanism is based on the signaling of
Label Distribution Protocol (LDP), which is applicable to PWs with a
dynamic control plane. [I-D.ietf-pals-endpoint-fast-protection]
describes a fast local repair mechanism for PW egress endpoint
failures, which is based on PW redundancy, upstream label assignment
and context specific label switching. The mechanism defined in
[I-D.ietf-pals-endpoint-fast-protection] is only applicable to PWs
with a dynamic control plane.
There is a need to support a dual-homing local protection mechanism
which avoids unnecessary switches of the AC or PW, and which can be
used regardless if a control plane is used. In some scenarios such
as mobile backhauling, the MPLS PWs are provisioned with dual-homing
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topology, in which at least the CE node on one side is dual-homed to
two PEs. If some fault occurs in the primary AC, operators usually
prefer to have the switchover only on the dual-homing PE side and
keep the working pseudowires unchanged if possible. This is to avoid
massive PW switchover in the mobile backhaul network due to the AC
failure in the mobile core site, which may in turn lead to congestion
due to the migration of traffic from the paths preferred by the
network planners. Similarly, as multiple PWs share the physical AC
in the mobile core site, it is preferable to keep using the working
AC when one working PW fails in PSN network, which could avoid
unnecessary switchover for other PWs. To meet the above
requirements, a fast dual-homing local PW protection mechanism is
needed to protect against the failures of an AC, the PE node, and the
PSN network.
This document describes the framework and several typical scenarios
of pseudowire (PW) dual-homing local protection. A Dual-Node
Interconnection (DNI) PW is used between the dual-homing PE nodes for
carrying traffic when a failure occurs in the AC or PW side. In
order for the dual-homing PE nodes to determine the forwarding state
of AC, PW and DNI PW, necessary state exchange and coordination
between the dual-homing PEs is needed. The necessary mechanisms and
protocol extensions are defined in a companion document
[I-D.ietf-pals-mpls-tp-dual-homing-coordination].
2. Reference Models of Dual-homing Local Protection
This section shows the reference architecture of the dual-homing PW
local protection and the usage of the architecture in different
scenarios.
2.1. PE Architecture
Figure 1 shows the PE architecture for dual-homing local protection.
This is based on the architecture in Figure 4a of [RFC3985]. In
addition to the AC and the service PW between the local and remote
PEs, a DNI PW is used to connect the forwarders of the dual-homing
PEs. It can be used to forward traffic between the dual-homing PEs
when a failure occurs in the AC or service PW side. As [RFC3985]
specifies: "any required switching functionality is the
responsibility of a forwarder function", in this case, the forwarder
is responsible for switching the payloads between three entities: the
AC, the service PW and the DNI PW.
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+----------------------------------------+
| Dual-homing PE Device |
+----------------------------------------+
AC | | | Service PW
<------>o Forwarder + Service X<===========>
| | PW |
+--------+--------+ |
| DNI PW | |
+--------X--------+----------------------+
^
| DNI PW
|
V
+--------X--------+----------------------+
| DNI PW | |
+--------+--------+ | Service PW
AC | | Service X<===========>
<------>o Forwarder + PW |
| | |
+----------------------------------------+
| Dual-homing PE Device |
+----------------------------------------+
Figure 1: PE Architecture for Dual-homing Protection
2.2. Dual-Homing Local Protection Reference Scenarios
2.2.1. One-Side Dual-Homing Protection
Figure 2 illustrates the network scenario of dual-homing PW local
protection where only one of the CEs is dual-homed to two PE nodes.
CE1 is dual-homed to PE1 and PE2, while CE2 is single-homed to PE3.
A DNI-PW is established between the dual-homing PEs, which is used to
bridge traffic when a failure occurs in the PSN network or in the AC
side. A dual-homing control mechanism enables the PEs and CE to
determine which AC should be used to carry traffic between CE1 and
the PSN network. The necessary control mechanisms and protocol
extensions are defined in a companion document
[I-D.ietf-pals-mpls-tp-dual-homing-coordination].
This scenario can protect the node failure of PE1 or PE2, or the
failure of one of the ACs between CE1 and the dual-homing PEs. In
addition, dual-homing PW protection can protect a failure occuring in
the PSN network which impacts the working PW, thus it can be an
alternative solution of PSN tunnel protection mechanisms. This
topology can be used in mobile backhauling application scenarios.
For example, CE2 might be a cell site equipment such as a NodeB,
whilst CE1 is the shared Radio Network Controller (RNC). PE3
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functions as an access side MPLS device while PE1 and PE2 function as
core side MPLS devices.
|<--------------- Emulated Service --------------->|
| |
| |<------- Pseudo Wire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC1 +----+ +----+ V
+-----+ | | PE1| | | +-----+
| |----------|........PW1.(working).......| | |
| | | | | | | |
| | +-+--+ | | AC3 | |
| | | | | | | |
| CE1 | DNI-PW | |PE3 |----------| CE2 |
| | | | | | |
| | +-+--+ | | | |
| | | | | | | |
| |----------|......PW2.(protection)......| | |
+-----+ | | PE2| | | +-----+
AC2 +----+ +----+
Figure 2. One-side dual-homing PW protection
Consider in normal state AC1 from CE1 to PE1 is initially active and
AC2 from CE1 to PE2 is initially standby, PW1 is the working PW and
PW2 is the protection PW.
When a failure occurs in AC1, then the state of AC2 changes to active
based on the AC dual-homing control mechanism. In order to keep the
switchover local and continue using PW1 for traffic forwarding as
preferred according to traffic planning, the forwarder on PE2 needs
to connect AC2 to the DNI PW, and the forwarder on PE1 needs to
connect the DNI PW to PW1. In this way the failure in AC1 will not
impact the forwarding of the service PWs across the network. After
the switchover, traffic will go through the bidirectional path: CE1-
(AC2)-PE2-(DNI-PW)-PE1-(PW1)-PE3-(AC3)-CE2.
When a failure in the PSN network affects the working PW (PW1),
according to PW protection mechanisms [RFC6378], traffic is switched
onto the protection PW (PW2), while the state of AC1 remains active.
Then the forwarder on PE1 needs to connect AC1 to the DNI PW, and the
forwarder on PE2 needs to connect the DNI PW to PW2. In this way the
failure in the PSN network will not impact the state of the ACs.
After the switchover, traffic will go through the bidirectional path:
CE1-(AC1)-PE1-(DNI-PW)-PE2-(PW2)-PE3-(AC3)-CE2.
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When a failure occurs in the working PE (PE1), it is equivalent to a
failure of the working AC, the working PW and the DNI PW. The state
of AC2 changes to active based on the AC dual-homing control
mechanism. And according to the PW protection mechanism, traffic is
switched on to the protection PW "PW2". In this case the forwarder
on PE2 needs to connect AC2 to PW2. After the switchover, traffic
will go through the bidirectional path: CE1-(AC2)-PE2-(PW2)-PE3-
(AC3)-CE2.
2.2.2. Two-side Dual-Homing Protection
Figure 3 illustrates the network scenario of dual-homing PW
protection where the CEs in both sides are dual-homed. CE1 is dual-
homed to PE1 and PE2, and CE2 is dual-homed to PE3 and PE4. A dual-
homing control mechanism enables the PEs and CEs to determine which
AC should be used to carry traffic between CE and the PSN network.
DNI-PWs are used between the dual-homing PEs on both sides. One
service PW is established between PE1 and PE3, another service PW is
established between PE2 and PE4. The role of working and protection
PW can be determined either by configuration or via existing
signaling mechanisms.
This scenario can protect the node failure on one of the dual-homing
PEs, or the failure on one of the ACs between the CEs and their dual-
homing PEs. Also, dual-homing PW protection can protect if the
failure occured in the PSN network which impacts one of the PWs, thus
it can be used as an alternative solution of PSN tunnel protection
mechanisms. Note, this scenario is mainly used for services
requiring high availability as it requires redundancy of the PEs and
network utilization. In this case, CE1 and CE2 can be regarded as
service access points.
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|<---------------- Emulated Service -------------->|
| |
| |<-------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC1 +----+ +----+ AC3 V
+-----+ | | ...|...PW1.(working)..|... | | +-----+
| |----------| PE1| | PE3|----------| |
| | +----+ +----+ | |
| | | | | |
| CE1 | DNI-PW1 | | DNI-PW2 | CE2 |
| | | | | |
| | +----+ +----+ | |
| | | | | | | |
| |----------| PE2| | PE4|--------- | |
+-----+ | | ...|.PW2.(protection).|... | | +-----+
AC2 +----+ +----+ AC4
Figure 3. Two-side dual-homing PW protection
Consider in normal state, AC1 between CE1 and PE1 is initially active
and AC2 between CE1 and PE2 is initially standby, AC3 between CE2 and
PE3 is initially active and AC4 from CE2 to PE4 is initially standby,
PW1 is the working PW and PW2 is the protection PW.
When a failure occurs in AC1, the state of AC2 changes to active
based on the AC dual-homing control mechanism. In order to keep the
switchover local and continue using PW1 for traffic forwarding, the
forwarder on PE2 needs to connect AC2 to the DNI-PW1, and the
forwarder on PE1 needs to connect DNI-PW1 with PW1. In this way
failures in the AC side will not impact the forwarding of the service
PWs across the network. After the switchover, traffic will go
through the bidirectional path: CE1-(AC2)-PE2-(DNI-PW1)-PE1-(PW1)-
PE3-(AC3)-CE2.
When a failure occurs in the working PW (PW1), according to the PW
protection mechanism [RFC6378], traffic needs to be switched onto the
protection PW "PW2". In order to keep the state of AC1 and AC3
unchanged, the forwarder on PE1 needs to connect AC1 to DNI-PW1, and
the forwarder on PE2 needs to connect DNI-PW1 to PW2. On the other
side, the forwarder of PE3 needs to connect AC3 to DNI-PW2, and the
forwarder on PE4 needs to connect PW2 to DNI-PW2. In this way, the
state of the ACs will not be impacted by the failure in the PSN
network. After the switchover, traffic will go through the
bidirectional path: CE1-(AC1)-PE1-(DNI-PW1)-PE2-(PW2)-PE4-(DNI-PW2)-
PE3-(AC3)-CE2.
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When a failure occurs in the working PE (PE1), it is equivalent to
the failures of the working AC, the working PW and the DNI PW. The
state of AC2 changes to active based on the AC dual-homing control
mechanism. And according to the PW protection mechanism, traffic is
switched on to the protection PW "PW2". In this case the forwarder
on PE2 needs to connect AC2 to PW2, and the forwarder on PE4 needs to
connect PW2 to DNI-PW2. After the switchover, traffic will go
through the bidirectional path: CE1-(AC2)-PE2-(PW2)-PE4-(DNI-PW2)-
PE3-(AC3)-CE2.
3. Generic Dual-homing PW Protection Mechanism
As shown in the above scenarios, with the described dual-homing PW
protection, failures in the AC side will not impact the forwarding
behavior of the PWs in the PSN network, and vice-versa.
In order for the dual-homing PEs to coordinate the traffic forwarding
during the failures, synchronization of the status information of the
involved entities and coordination of switchover between the dual-
homing PEs are needed. For PWs with a dynamic control plane, such
information synchronization and coordination can be achieved with a
dynamic protocol, such as [RFC7275], possibly with some extensions.
For PWs which are manually configured without a control plane, a new
mechanism is needed to exchange the status information and coordinate
switchover between the dual-homing PEs, e.g. over an embedded PW
control channel. This is described in a companion document
[I-D.ietf-pals-mpls-tp-dual-homing-coordination].
4. IANA Considerations
This document does not require any IANA action.
5. Security Considerations
The scenarios defined in this document do not affect the security
model as defined in [RFC3985].
With the proposed protection mechanism, the disruption of a dual-
homed AC, a component which is outside the core network, would have a
reduced impact on the traffic flows in the core network. This could
also avoid unnecessary congestion in the core network.
The security consideration of the DNI PW is the same as for Service
PWs in the data plane [RFC3985]. Security considerations for the
coordination/control mechanism will be addressed in the companion
document that defines the mechanism.
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6. Contributors
The following individuals substantially contributed to the content of
this document:
Kai Liu
Huawei Technologies
Email: alex.liukai@huawei.com
Alessandro D'Alessandro
Telecom Italia
alessandro.dalessandro@telecomitalia.it
7. References
7.1. Normative References
[I-D.ietf-pals-mpls-tp-dual-homing-coordination]
Cheng, W., Wang, L., Li, H., Dong, J., and A.
D'Alessandro, "Dual-Homing Coordination for MPLS Transport
Profile (MPLS-TP) Pseudowires Protection", draft-ietf-
pals-mpls-tp-dual-homing-coordination-05 (work in
progress), January 2017.
[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>.
7.2. Informative References
[I-D.ietf-pals-endpoint-fast-protection]
Shen, Y., Aggarwal, R., Henderickx, W., and Y. Jiang, "PW
Endpoint Fast Failure Protection", draft-ietf-pals-
endpoint-fast-protection-05 (work in progress), January
2017.
[RFC6372] Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
Profile (MPLS-TP) Survivability Framework", RFC 6372,
DOI 10.17487/RFC6372, September 2011,
<http://www.rfc-editor.org/info/rfc6372>.
[RFC6378] Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher,
N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-
TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378,
October 2011, <http://www.rfc-editor.org/info/rfc6378>.
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[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>.
[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>.
[RFC7275] Martini, L., Salam, S., Sajassi, A., Bocci, M.,
Matsushima, S., and T. Nadeau, "Inter-Chassis
Communication Protocol for Layer 2 Virtual Private Network
(L2VPN) Provider Edge (PE) Redundancy", RFC 7275,
DOI 10.17487/RFC7275, June 2014,
<http://www.rfc-editor.org/info/rfc7275>.
Authors' Addresses
Weiqiang Cheng
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: chengweiqiang@chinamobile.com
Lei Wang
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: Wangleiyj@chinamobile.com
Han Li
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: Lihan@chinamobile.com
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Shahram Davari
Broadcom Corporation
3151 Zanker Road
San Jose 95134-1933
United States
Email: davari@broadcom.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
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