Internet DRAFT - draft-cheng-mpls-tp-pwe3-dual-homed-protection
draft-cheng-mpls-tp-pwe3-dual-homed-protection
Network Working Group WQ. Cheng
Internet-Draft L. Wang
Intended status: Standards Track H. Li
Expires: April 24, 2014 China Mobile
K. Liu
Huawei Technologies Co., Ltd.
S. Davari
Broadcom Corporation
October 21, 2013
MPLS-TP PWE3 dual-homed protection (MPDP)
draft-cheng-mpls-tp-pwe3-dual-homed-protection-00
Abstract
This document presents the requirements for Dual-homed protection in
the MPLS-TP networks and defines a protocol that can protect the
failure of an attachment circuit (AC) or the failure of a provider
edge (PE) node or the failure of a pseudowire (PW) in the packet-
switched network (PSN).
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Application scenarios of Dual-Homed protection . . . . . . . 3
2.1. One-side Dual-Homing topology . . . . . . . . . . . . . . 4
2.2. Two-side Dual-Homing topology . . . . . . . . . . . . . . 4
3. PWE3 dual-homed protection mechanism . . . . . . . . . . . . 5
3.1. Multi-chassis PW protection . . . . . . . . . . . . . . . 5
3.2. Multi-chassis LAG . . . . . . . . . . . . . . . . . . . . 7
4. Three point-switch collaboration . . . . . . . . . . . . . . 8
5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. Author's Addresses . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The linear protection and Ring protection mechanisms for MPLS-TP is
described in RFC 6378, RFC 6974 and other IETF drafts. These
mechanisms work within the PSN and provide fast recovery when link
failure or P node failure occurs. However, they are unable to
protect against the failure of a PE node or the failure of an
attachment circuit.
The PW redundancy solution which is defined by RFC 6718 requires
separate mechanisms to recover the PE and AC link failure from the
PSN failure.
The operators need an end-to-end network's survivability for
guaranteed services, so the protection mechanisms for AC,PE and
failure within PSN are all needed. In order to meet the requirement,
multiple layers and across nested recovery domains protection should
be deployed. It raised the following issues:
o longer recovery time, because hold-off time should be set to avoid
race scenarios, which makes the switching time longer.
o lower bandwidth efficiency because of multi-layer protections.
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o extra configuration makes the operation and maintenance more
complicated.
o if RFC 6718 is used, the AC link failure will result in protection
switching performed within PSN, that means the failure of an AC are
propagated to the remote PEs on the other side of the network.
In order to improve on RFC 6718, dual-homed protection mechanism
should meet the following requirements
O Using a single layer protection for PSN,AC and PE failure
PWE3 Dual-Homed protection needs to recover PE failures, tunnel
failures within PSN and AC link failures through a single layer
protection mechanism so that the multi-layer protection can be
avoided.
O Independent failure recovery
The principle of independent failure recovery is that the protection
switching is solely performed within the network domain where the
failure takes place. For instance, When a failure in a an AC
happens, there is no need to inform the remote PE about the failure
and there is no need to change the PW and path in the PSN.
O To deploy dual-homed network protection, as far as protocols which
PE previously support, such as linear protection protocol, can be
reused, upgrading remote PEs should be avoided.
According to RFC5654 "2.5.6. Topology-Specific Recovery Mechanisms",
"MPLS-TP MAY support recovery mechanisms that are optimized for
specific network topologies. These mechanisms MUST be interoperable
with the mechanisms defined for arbitrary topology (mesh) networks to
enable the protection of end-to-end transport paths ",this document
presents a single layer dual-homed protection to meet those
requirements.
2. Application scenarios of Dual-Homed protection
The application scenarios of Dual-homed protection can be classified
into a One-side Dual-Homing topology and a Two-side Dual-homing
topology.
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2.1. One-side Dual-Homing topology
|------------- Emulated Service ------------|
| |
| |-------- Pseudo Wire -------| |
| | | |
| | |--- PSN Tunnels---| | |
| V V V V |
V AC +----+ +----+ V
+-----+ | | PE1| | | +-----+
| |-------|....|...PW1.(active)...|....| | |
| | | | | | | |
| | +----+ | | AC | |
| | || | | | | |
| CE1 | DNI |PE2 |------| CE2 |
| | || | | | |
| | +----+ | | | |
| | | | | | | |
| |-------|....|...PW2.(standby)..|....| | |
+-----+ | | PE3| | | +-----+
AC +----+ +----+
Figure 1 One-side PW Dual-Homing protection
Figure 1 illustrates the network scenario of one-side CE dual-homing
topology. The dual-homing gateways for CE1 are PE1 and PE3, while
PE2 is the single-homing for CE2. This scheme protects the node
failures of PE1 and PE3 and the link failures between PE1 and CE1/PE3
and CE1. This scheme can be used in back hauling application
scenarios. For example, nodeB serves for CE2 while RNC serves for
CE1. PE2 works as an access layer MPLS-TP device while PE1 and PE3
works as a a pair of core layer MPLS-TP devices.
2.2. Two-side Dual-Homing topology
|------------- Emulated Service -------------|
| |
| |--------- Pseudowire -------| |
| | | |
| | |--- PSN Tunnels---| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | |....|.......PW1........|....| | +-----+
| |------| PE1| | PE2|--------| |
| | +----+ +----+ | |
| | || || | |
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| CE1 | DNI DNI | CE2 |
| | || || | |
| | +----+ +----+ | |
| | | | | | | |
| |------| PE3| | PE4|------- | |
+-----+ | |....|.....PW2..........|....| | +-----+
AC +----+ +----+ AC
Figure 2 dual-side PW Dual-Homing protection
Figure 2 illustrates the network scenario of two-side CE dual-homing.
The dual- homing nodes are PE1 and PE3 for CE1, and PE2 and PE4 for
CE2, respectively. This scenario protects the PE1/PE3 and PE2/PE4
nodes failures. It also protects the links failure between PE1 and
CE1, PE3 and CE1, PE2 and CE2, and PE4 and CE2. Meanwhile, dual-
homing protection needs to handle the recovery of PSN Tunnel failure
as well. As for broadband services provider, this scenario is mainly
used in services for important business customers. Here, CE1 and CE2
can be regarded as service access points.
3. PWE3 dual-homed protection mechanism
In a PWE3 dual-homed protection mechanism, Multi-chassis PW
protection is used between PEs, Multi-chassis LAG is used between
dual-homed PE node group.
3.1. Multi-chassis PW protection
RFC6738(MPLS Transport Profile (MPLS-TP) Linear Protection) and ITU-T
G.8131 have defined linear protection mechanism for MPLS-TP network.
The PEs of working PW are the same as its protecting PW and the
protection switching mechanism is running on each PE.
Dual-homed PW protection mechanism keeps the same protection
switching mechanism with linear protection in the Remote PE (PE3 in
figure 3) and the working PW and protecting PW are terminated in
Dual-homed PEs (PE1 and PE2 in figure 3) respectively in order to
protect Dual-homed PEs.The protection switching mechanism will be
detailed in the following chapters.
Dual nodes interconnection (DNI) PW is set up between two dual-homed
PE nodes, and it is used to bridge traffic when failure occurs.
Messages between two dual-homed node include channel status notify
message and protection group status notify message. The format of
these messages is TBD.
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+--------------------+ +--------+
| | | |
| PE1 | Working PW | |
| +-----------------------| |
| | |\ | |
| | | \ | |
| | | \ | |
| | | \ | |
+-------------|------+ \ | |
DNI PW MC PW Protection | PE3 |
| / | |
+-------------|------+ / | |
| | | / | |
| | | / | |
| | |- protection PW | |
| +-----------------------| |
| | | |
| PE2 | | |
+--------------------+ +--------+
Figure 3 MC PW linear protection mechanism
The failure scenarios are listed as follows:
O One direction Failure of Working PW (PE1 to PE3):
PE3 detects failure and sends PSC or APS message in protection PW.
When PE2 receives the failure information, it will exchange a
switching message with PE3. At last, PE2 and PE3 will switch the
traffic to the protection PW. PE2 will periodically send PE1 MC PW
protection group status messages,and then PE1 will execute the
switching according to the status of the MC PW protection.
O One direction Failure of Working PW (PE3 to PE1):
PE1 will detect the failure and send PE2 a MC PW protection message
to notify work PW failure through DNI PW. PE2 will execute the
switch with PE3 based on PSC or APS. PE2 will periodically send PE1
MC PW protection group status messages, and PE1 will execute
switching according to the status of the MC PW protection.
O Bi-direction Failure of Working PW (Between PE3 and PE1):
Both of PE1 and PE3 will detect link fault respectively. PE3
executes switching to protection PW based on APS or PSC. PE1 sends
PE2 a MC PW protection message to notify working PW failure through
DNI PW,and then PE2 will execute switching to protection PW. PE2
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will periodically send PE1 MC PW protection group status messages,
and PE1 will execute switching according to the status of the MC PW
protection.
O Working PE failure:
PE3 will detect failure, and send PSC or APS message in the
protection PW. After PE2 exchanges the switching message with PE3,
PE2 and PE3 will switch traffic to the protection PW.
3.2. Multi-chassis LAG
LAG(Link Aggregation Group) and LACP(Link Aggregation control
protocol) is defined in IEEE802.1ax. LAG is used to expand bandwidth
and protect link failure.
DRNI (Distributed Resilient Network Interconnect) and DRCP
(Distributed Relay Control Protocol) is defined in IEEE P802.1AX-
REV-D2.2. DRNI expands the concept of Link Aggregation so that, at
either one or both ends of a Link Aggregation Group, the single
Aggregation System is replaced by a Portal, composed from one to
three Portal Systems.
In the document, DRNI is used to protect Ethernet link failure
between CE and PE and dual-homed node Failure on the CE side as shown
in figure 4.
O Working PE failure: Detailed signaling between PE1, PE2, CE is TBD
+-----------+ +--------+
| PE1 | | |
| +----+| Ethernet |+----+ |
| |port|-------------||port| |
| +----+| /|+----+ |
+-------|---+ | | |
| \ | | |
DRCP DRNI LAG | CE |
| / | | |
+-------|---+ | | |
| PE2 | | | | |
| +----+| \|+----+ |
| |port||------------||port| |
| +----+| Ethernet |+----+ |
+-----------+ +--------+
Figure 4 DRNI mechanism
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4. Three point-switch collaboration
In dual-homed PE nodes, the protection mechanism in PSN network(MC PW
protection) and protection mechanism between PE and CE(DRNI) should
cooperate to ensure an appropriate switch operation.
+------------+ +------------------+
| PE3 | | PE1 |
| +---+| service PW |+---+ +---+|
| |PW1|--------------|PW1| |AC1||
| +---+| |+---+ +---+|
| | | +------+ |
| | | |DNI PW| |
| | | +------+ |
| | +------------------+
| | ||
| | ||DNI PW
| | ||
| | +------------------+
| | | +------+ |
| | | |DNI PW| |
| | | +------+ |
| | | |
| +---+| service PW |+---+ +---+|
| |PW2|--------------|PW2| |AC1||
| +---+| |+---+ PE2 +---+|
+------------+ +------------------+
Figure 6 three point status machine
Service PW is the PW which carry service between dual-homed PE and
remote PE. Service PW status is decided by MC PW protection
mechanism.
DNI PW is the bridge PW between two dual-homed PE nodes. It is used
to bridge traffic when PSN tunnel or AC failure occurs.
AC status is the status of AC port between dual-homed PW and CE,
being either active or standby. It is decided by DRNI mechanism.
+--------+--------+--------+---------+--------+
|srv PW | AC | PW fwd | DNI fwd | AC fwd |
+--------+--------+--------+---------+--------+
| Active | Active | to AC | to PW | to PW |
+--------+--------+--------+---------+--------+
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| Active | Standby| to DNI | to PW | to PW |
+--------+--------+--------+---------+--------+
| Standby| Active | to AC | to AC | to DNI|
+--------+--------+--------+---------+--------+
| Standby| Standby| to DNI | to AC | to DNI|
+--------+--------+--------+---------+--------+
Figure 7 three point status machine in dual-homed nodes
The principle of three point status machine in dual-homed nodes:
O If AC status is active, establish connection from service PW to AC.
If AC status is standby, establish connection from service PW to DNI
PW.
O If service PW is active, establish connection from AC to service
PW. If service PW status is standby, establish connection from AC to
DNI PW.
O If service PW is active, establish connection from DNI PW to
service PW. If service PW status is standby, establish connection
from DNI PW to AC.
5. Formal Syntax
None
6. Security Considerations
None
7. Acknowledgments
None
8. Author's Addresses
None
9. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
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[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile",
RFC 5654, September 2009.
[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.
[RFC6974] Weingarten, Y., Bryant, S., Ceccarelli, D., Caviglia, D.,
Fondelli, F., Corsi, M., Wu, B., and X. Dai,
"Applicability of MPLS Transport Profile for Ring
Topologies", RFC 6974, July 2013.
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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Kai Liu
Huawei Technologies Co., Ltd.
Huawei base, Bantian, Longgang District
Shenzhen 518129
China
Email: alex.liukai@huawei.com
Shahram Davari
Broadcom Corporation
3151 Zanker Road
San Jose, CA 95134-1933
Email: davari@broadcom.com
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