Internet DRAFT - draft-cheng-pwe3-mpls-tp-dual-homing-protection
draft-cheng-pwe3-mpls-tp-dual-homing-protection
Network Working Group W. Cheng
Internet-Draft L. Wang
Intended status: Standards Track H. Li
Expires: April 30, 2015 China Mobile
K. Liu
Huawei Technologies
S. Davari
Broadcom Corporation
J. Dong
Huawei Technologies
A. D'Alessandro
Telecom Italia
October 27, 2014
Dual-Homing Protection for MPLS and MPLS-TP Pseudowires
draft-cheng-pwe3-mpls-tp-dual-homing-protection-01
Abstract
This document describes a framework and several scenarios for
pseudowire (PW) dual-homing local protection. A Dual-Node
Interconncetion (DNI) PW is provisioned between the dual-homing
Provider Edge (PE) nodes for carrying traffic when failure accurs in
the Attachment Circuit (AC) or PW side. In order for the dual-homing
PE nodes to determine the forwarding state of AC, PW and the DNI PW,
necessary state exchange and coordination between the dual-homing PEs
are needed. The PW dual-homing local protection mechanism is
complementary to the existing PW protection mechanisms.
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
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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 April 30, 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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 . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[RFC6372] and [RFC6378] describe the framework and mechanism of MPLS-
TP Linear protection, which can provide protection for the MPLS LSP
or PW between the edge nodes. Such mechanism does not protect the
failure of the Attachement 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-pwe3-endpoint-fast-protection]
describes a fast local repair mechanism for PW egress endpoint
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failures, which is based on PW redundancy, upstream label assignment
and context specific label switching. Such mechanism is applicable
to PWs with a dynamic control plane.
In some scenarios such as mobile backhauling, the MPLS PWs are
provisioned with dual-homing topology, in which at least the CE node
in one side is dual-homed to two PEs. If some fault occurs in the
primary AC, operators usually prefer to have the switchover only in
the dual-homing PE side and keeps the working pseudowires unchanged
if possible. This is to avoid massive PWs switchover in the mobile
backhaul network due to one AC failure in the core site, and also
could achieve efficient and balanced link bandwidth utilization.
Similarly, it is preferable to keep using the working AC when one
working PW fails in the PSN network. To meet the above requirement,
a fast dual-homing PW local protection mechanism is needed to protect
the failures in AC, the PE node and the PSN network.
This document describes a framework and several scenarios for
pseudowire (PW) dual-homing local protection. A Dual-Node
Interconncetion (DNI) PW is provisioned between the dual-homing
Provider Edge (PE) nodes for carrying traffic when failure accurs 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
mechanism defined in this document is complementary to the existing
protection mechanisms. The neccessary protocol extensions will be
described in a seperate document.
The proposed mechanism has been deployed in several mobile backhaul
networks which use static MPLS-TP PWs for the backhauling of mobile
traffic.
2. Reference Models of Dual-homing Local Protection
This section shows the reference architecture of the PE for 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, a DNI PW is provisioned to
connect the forwarders of the dual-homing PEs. It can be used to
forward traffic between the dual-homing PEs when failure accurs 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
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the payloads between three entities: the AC, the service PW and the
DNI PW. The specific behavior of forwarder is determined according
to the forwarding state machine defined in this document.
+----------------------------------------+
| Dual-homing PE Device |
Single +----------------------------------------+
AC | | | Service PW
<------>o Forwarder + Service X<===========>
| | PW |
+--------+--------+ |
| DNI PW | |
+--------X--------+----------------------+
^
| DNI PW
|
V
+--------X-------------------------------+
| Peer 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 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. 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 control mechanism enables the PEs and CE to determine which
AC should be used to carry traffic between CE1 and the PSN network.
These mechanisms/protocols are beyond the scope of this document.
The working and protection PWs can be determined either by
configuration or by existing signaling mechanisms.
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 the failure occured
in the PSN network which impacts the working PW, thus it can be an
alternative to PSN tunnel protection mechanisms. This topology can
be used in mobile backhauling application scenarios. For example,
the NodeB serves as CE2 while the RNC serves as CE1. PE3 works as an
access side MPLS device while PE1 and PE2 works as core side MPLS
devices.
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|<--------------- 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 some AC redundancy mechanism. In order to keep the
switchover local and continue using PW1 to forward traffic, the
forwarder on PE2 needs to connect AC2 to the DNI PW, and the
forwarder on PE1 needs to connect the DNI PW to the PW1. In this way
the failure in the AC1 do not impact the forwarding of the service
PWs across the network. After the switchover, traffic will go
through the 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, 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 do not impact the state of the ACs. After
the switchover, traffic will go through the path: CE1-(AC1)-PE1-(DNI-
PW)-PE2-(PW2)-PE3-(AC3)-CE2.
In both AC and PW failure cases, the dual-homing PW protection needs
to coordinate the PEs to set the forwarding state between the AC,
service PW and DNI PW properly.
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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.
The DNI-PWs are provisioned between the dual-homing PEs on both side.
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 mechansims.
This scenario can protect the node failure of one of the dual-homing
PEs, or the failure of one of the ACs between the CEs and their dual-
homing PEs. Meanwhile, dual-homing PW protection can protect the
failure occured in the PSN network which impacts one of the PWs, thus
it can be an alternative to PSN tunnel protection mechanisms. This
scenario is mainly used for services provisioning for important
business customers. In this case, CE1 and CE2 can be regarded as
service access points.
|<---------------- 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 from CE1 to PE1 is initially active and
AC2 from CE1 to PE2 is initially standby, AC3 from CE2 to PE3 is
initially active and AC4 from CE2 to PE4 is initially standby, PW1 is
the working PW and PW2 is the protection PW.
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When a failure occurs in AC1, the state of AC2 changes to active
based on some AC redundancy mechanism. In order to keep the
switchover local and continue using PW1 to forward traffic, the
forwarder on PE2 needs to connect AC2 to the DNI PW, and the
forwarder on PE1 needs to connect the DNI PW with PW1. In this way
failures in the AC side do not impact the forwarding of the service
PWs across the network. After the switchover, traffic will go
through the 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, traffic is 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 the DNI-PW1, and the
forwarder on PE2 needs to connect the DNI-PW1 to PW2. On the other
side, the forwarder of PE3 needs to connect AC3 to the DNI-PW2, and
the forwarder on PE4 needs to connect PW2 to the 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 path:
CE1-(AC1)-PE1-(DNI-PW1)-PE2-(PW2)-PE4-(DNI-PW2)-PE3-(AC3)-CE2.
In both AC and PW failure cases, the dual-homing PW protection needs
to coordinate the PEs to set the forwarding state between the AC,
service PW and the DNI PW properly.
3. Generic Dual-homing PW Protection Mechanism
As shown in the above scenarios, with the described Dual-Homing PW
Protection, the failures in the AC side do not impact the forwarding
behavior of the PWs in the PSN network, and vice-versa. This is
achieved by properly setting the forwarding state between the
following entities:
o AC
o Service PWs
o DNI PW
The forwarding behavior of the dual-homing PE nodes are determined by
the forwarding state machine as shown in table 1:
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+-----------+---------+--------+---------------------+
|Service PW | AC | DNI PW | Forwarding Behavior |
+-----------+---------+--------+---------------------+
| Active | Active | Up |Service PW <-> AC |
+-----------+---------+--------+---------------------+
| Active | Standby | Up |Service PW <-> DNI PW|
+-----------+---------+--------+---------------------+
| Standby | Active | Up | DNI PW <-> AC |
+-----------+---------+--------+---------------------+
| Standby | Standby | Up | Drop all packets |
+-----------+---------+--------+---------------------+
Table 1. Dual-homing PE Forwarding State Machine
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 sychronization 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. This is described in a
separate document.
4. IANA Considerations
This document does not require any IANA action.
5. Security Considerations
The mechanism defined in this document do not affect the security
model as defined in [RFC3985].
6. References
6.1. Normative References
[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.
6.2. Informative References
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[I-D.ietf-pwe3-endpoint-fast-protection]
Shen, Y., Aggarwal, R., Henderickx, W., and Y. Jiang, "PW
Endpoint Fast Failure Protection", draft-ietf-pwe3-
endpoint-fast-protection-01 (work in progress), July 2014.
[RFC6372] Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS-
TP) Survivability Framework", RFC 6372, September 2011.
[RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
Protection", RFC 6378, October 2011.
[RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", RFC 6718, August 2012.
[RFC6870] Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", RFC 6870, February 2013.
[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, June
2014.
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
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Han Li
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: Lihan@chinamobile.com
Kai Liu
Huawei Technologies
Huawei Base, Bantian, Longgang District
Shenzhen 518129
China
Email: alex.liukai@huawei.com
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
Alessandro D'Alessandro
Telecom Italia
via Reiss Romoli, 274
Torino 10148
Italy
Email: alessandro.dalessandro@telecomitalia.it
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