Networking Working Group Z. Liu
Internet-Draft China Telecom
Intended status: BCP L. Jin
Expires: August 12, 2014
R. Chen
ZTE Corporation
D. Cai
S. Salam
Cisco
February 8, 2014
Redundancy provisioning for VPLS Inter-domain
draft-ietf-l2vpn-vpls-inter-domain-redundancy-04
Abstract
In many existing Virtual Private LAN Service (VPLS) deployments based
on RFC4762, inter-domain connectivity has been deployed without node
redundancy, or with node redundancy in a single domain. This
document describes a solution for inter-domain VPLS based on RFC4762
with node and link redundancy in both domains.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 12, 2014.
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
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Network Use Case . . . . . . . . . . . . . . . . . . . . . . . 4
5. PW redundancy application procedure for inter-domain
redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. ICCP switchover condition . . . . . . . . . . . . . . . . 6
5.1.1. Inter-domain PW failure . . . . . . . . . . . . . . . 6
5.1.2. PE node isolation . . . . . . . . . . . . . . . . . . 6
5.1.3. PE node failure . . . . . . . . . . . . . . . . . . . 6
5.2. Inter-domain redundancy with two-PWs . . . . . . . . . . . 6
5.3. Inter-domain redundancy with four-PWs . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative references . . . . . . . . . . . . . . . . . . . 9
10.2. Informative references . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
In many existing Virtual Private LAN Service (VPLS) deployments based
on [RFC4762], inter-domain connectivity has been deployed without
node redundancy, or with node redundancy in a single domain. This
document describes a solution for inter-domain VPLS based on
[RFC4762] with node and link redundancy in both domains. The domain
in this document refers to autonomous system (AS), or other
administrative domains.
2. Conventions used in this document
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 [RFC2119].
3. Motivation
Inter-AS VPLS offerings are widely deployed in service provider
networks today. Typically, the ASBRs and associated physical links
that connect the domains carry a multitude of services. As such, it
is important to provide link and node redundancy, to ensure service
high availability and meet end customer service level
agreements(SLAs).
Several current deployments of inter-AS VPLS are implemented like
Inter-AS option A in [RFC4364] section 10, where VLANs are used to
hand-off the services between two domains. In these deployments,
link/node redundancy is achieved using MC-LAG (Multi-Chassis Link
Aggregation) and [I-D.ietf-pwe3-iccp]. This, however, places two
restrictions on the interconnection: the two domains must be
interconnected using Ethernet links, and the links must be
homogeneous, i.e. of the same speed, in order to be aggregated.
These two conditions cannot always be guaranteed in live deployments.
For instance, there are many scenarios where the interconnect between
the domains uses Packet over Sonet/SDH (POS), thereby ruling out the
applicability of MC-LAG as a redundancy mechanism. As such, from a
technical point of view, it is desirable to use PWs to interconnect
the VPLS domains, and to offer resiliency using PW redundancy
mechanisms.
MP-BGP can be used for VPLS inter-domain protection, as described in
[RFC6074], using either option B or option C inter-AS models.
However, with this solution, the protection time relies on BGP
control plane convergence. In certain deployments, with tight SLA
requirements on availability, this mechanism may not provide the
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desired failover time characteristics. Furthermore, in certain
situations MP-BGP is not deployed for VPLS. The redundancy solution
described in this draft reuses ICCP [I-D.ietf-pwe3-iccp] and PW
redundancy [RFC6718] to provide fast convergence.
Furthermore, in the case where Label Switched Multicast is not used
for VPLS multicast [I-D.ietf-l2vpn-vpls-mcast], the solution
described here provides a better behavior compared to inter-AS option
B: with option B, each PE must perform ingress replication to all
other PEs in its local as well as the remote domain. Whereas, with
the ICCP solution, the PE only replicates to local PEs and to the
Autonomous System Border Router (ASBR). The ASBR then sends traffic
P2P to the remote ASBR, and the remote ASBR replicates to its local
PEs. As a result, the load of replication is distributed and is more
efficient than option B.
Two PW redundancy modes defined in [RFC6718], namely independent mode
and master/slave mode, are applicable in this solution. In order to
maintain control plane separation between two domains, the
independent mode is preferred by operators. The master/slave mode
provides some enhanced capabilities and, hence, is included in this
draft.
4. Network Use Case
There are two network use cases for VPLS inter-domain redundancy:
two-PWs redundancy case, and four-PWs redundancy case.
Figure 1 presents an example use case with two inter-domain PWs.
Provider Edge (PE) 3/PE4/PE5/PE6 may be ASBRs of their respective AS,
or VPLS PEs within its own AS. A deployment example of this use case
is where there are only two physical links between two domains and
PE3 is physically connected with PE5, and PE4 is physically connected
with PE6.
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+---------+ +---------+
+---+ | +-----+ | active PW1 | +-----+| +---+
|PE1|---|-| PE3 |-|-----------------|--| PE5 ||----|PE7|
+---+\ |/+-----+ | | +-----+\ /+---+
| \ / | * | | * | |\ / |
| \| | |ICCP| |ICCP| | | \ |
| / \ | * | | * | |/ \ |
+---+/ |\+-----+ | | +-----+/ \+---+
|PE2|---|-| PE4 |-|-----------------|--| PE6 ||----|PE8|
+---+ | +-----+ | standby PW2 | +-----+| +---+
| | | |
| | | |
| RG1 | | RG2 |
+---------+ +---------+
operator A network operator B network
Figure 1
Figure 2 presents a four-PWs inter-domain VPLS redundancy use-case.
PE3/PE4/PE5/PE6 may be ASBRs of their respective AS, or VPLS PEs
within its own AS, A deployment example of this use case is where
there are four physical links between two domains and four PEs are
physically connected with each other with four links.
+---------+ +---------+
+---+ | +-----+ | | +-----+| +---+
|PE1|---|-| PE3 |-|--------PW1------|--| PE5 ||----|PE7|
+---+\ |/+-----+ |-PW3-\ /-------| +-----+\ /+---+
| \ / | * | \ / | * | |\ / |
| \| | |ICCP| X |ICCP| | | \ |
| / \ | * | / \ | * | |/ \ |
+---+/ |\+-----+ |-PW4-/ \-------| +-----+/ \+---+
|PE2|---|-| PE4 |-|----PW2----------|--| PE6 ||----|PE8|
+---+ | +-----+ | | +-----+| +---+
| | | |
| | | |
| RG1 | | RG2 |
+---------+ +---------+
operator A network operator B network
Figure 2
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5. PW redundancy application procedure for inter-domain redundancy
PW redundancy application procedures are described in section 9.1 of
[I-D.ietf-pwe3-iccp]. When a PE node encounters a failure, the other
PE takes over. This document reuses the PW redundancy mechanism
defined in[I-D.ietf-pwe3-iccp], with new ICCP switchover conditions
as specified in following section.
There are two PW redundancy modes defined in [RFC6870]: Independent
mode and Master/Slave mode. For the inter-domain four-PW scenario,
it is required for PEs to ensure that the same mode is supported on
the two ICCP peers in the same redundancy group (RG).
5.1. ICCP switchover condition
5.1.1. Inter-domain PW failure
When a PE receives advertisements from the active PE, in the same RG,
indicating that all the inter-domain PW status has changed to DOWN/
STANDBY, then if it has the highest priority (after the advertising
PE), it SHOULD advertise active state for all of its associated
inter-domain PWs.
5.1.2. PE node isolation
When a PE detects failure of all PWs to the local domain, it SHOULD
advertise standby state for all its inter-domain PWs to trigger
remote PE to switchover.
5.1.3. PE node failure
When a PE node detects that the active PE, that is member of the same
RG, has gone down, if the local PE has redundant PWs for the affected
services and has the highest priority (after the failed PE), it
advertises the active state for all associated inter-domain PWs.
5.2. Inter-domain redundancy with two-PWs
In this use case, it is recommended that the operation be as follows:
o ICCP deployment option: ICCP is deployed on VPLS edge nodes in
both domains;
o PW redundancy mode: independent mode only;
o Protection architectures: 1:1(1 standby, 1 active).
The switchover rules described in section 5.1 apply. Before
deploying this inter-domain VPLS, the operators MUST negotiate to
configure same PW high/low priority at two PW end-points. E.g, in
figure 1, PE3 and PE5 MUST both have higher/lower priority than PE4
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and PE6, otherwise both PW1 and PW2 will be in standby state.
5.3. Inter-domain redundancy with four-PWs
In this use case, there are generally three options to provide 1:1
protection or 3:1 protection. The inter-domain PWs that connect to
the same PE should have proper PW priority to advertise same active/
standby state. E.g, in figure 2, both PW1 and PW3 connected to PE3
would advertise active/standby state.
For 1:1 protection model, the operation would be as follows:
o ICCP deployment option: ICCP is deployed on VPLS edge nodes in
both domains;
o PW redundancy mode: independent mode only;
o Protection architectures: 1:1(1 standby, 1 active).
The switchover rules described in section 5.1 apply. In this case,
the operators do not need to do any coordination of the inter-domain
PW priority. The PE detecting one PW DOWN should set the other PW to
STANDBY if available, and then synchronize the updated state to its
ICCP peer. When a PE detects that the PWs from ICCP peer PE are DOWN
or STANDBY, it should switchover as described in section 5.1.1.
There are two variants of the 3:1 protection model. We will refer to
them as option A and B. For option A of the 3:1 protection model, the
support of 'request switchover' bit is required. The operation is as
follows:
o ICCP deployment option: ICCP is deployed on VPLS edge nodes in
both domains;
o PW redundancy mode: Independent mode with 'request switchover' bit
support;
o Protection architectures: 3:1 (3 standby, 1 active).
In this case, the procedure on the PE for the PW failure is per
section 6.3 of [RFC6870], and with the following additions:
o When the PE detects failure of the active inter-domain PW, it
should switch to the other local standby inter-domain PW if
available, and send an updated LDP pseudowire status message with
the 'request switchover' bit set on that local standby inter-
domain PW to the remote PE;
o Local and remote PE should also update the new PW status to their
ICCP peers, respectively, in Application Data Messages with PW-RED
Synchronization Request TLV for corresponding service, so as to
synchronize the latest PW status on both PE sides;
o While waiting for the acknowledgment, the PE that sent the
'request switchover' bit may receive a switchover request from its
ICCP peer's PW remote endpoint by virtue of the ICCP
synchronization. The PE MUST compare IP addresses with that PW
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remote peer. The PE with a higher IP address will ignore the
request and continue to wait for the acknowledgement from its peer
in the remote domain. The PE with the lower IP address MUST clear
'request switchover' bit and set 'Preferential Forwarding' local
status bit, and update the PW status to ICCP peer.
o The remote PE receiving 'request switchover' bit will acknowledge
the request and activate the PW only when it is ready to take over
as described in section 5.1, otherwise, it MUST ignore the
request.
The node isolation failure and node failure is described in section
5.1.
For option B of 3:1 protection model, master/slave mode support is
required, and should be as follows:
o ICCP deployment option: ICCP is deployed on VPLS edge nodes in
only one domain;
o PW redundancy mode: master/slave only;
o Protection architectures: 3:1 (3 standby, 1 active).
When master/slave PW redundancy mode is employed, the network
operators of two domains must agree on which domain PEs will be
master, and configure the devices accordingly. The inter-domain PWs
that connect to one PE should have higher PW priority than the PWs on
the other PE in the same RG. The procedure on the PE for PW failure
is as follows:
o The PE with higher PW priority should only enable one PW active,
and the other PWs standby.
o When the PE detects active PW DOWN, it should enable the other
local standby PW to be active with preference. Only when two
inter-domain PWs connect to the PE are DOWN, the ICCP peer PE in
the same RG would switchover as described in section 5.1.
The node isolation failure and node failure is described in section
5.1.
6. Security Considerations
This draft will have the same security properties of
[I-D.ietf-pwe3-iccp] and [RFC4762]
7. IANA Consideration
No IANA allocation is required in this draft.
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8. Acknowledgements
The author would like to thank Sami Boutros, Giles Heron for their
valuable comments.
9. Contributors
Daniel Cohn
Email:daniel.cohn.ietf@gmail.com
Yubao Wang
ZTE Corporation
Nanjing, China
Email: wang.yubao@zte.com.cn
10. References
10.1. Normative references
[I-D.ietf-pwe3-iccp]
Martini, L., Salam, S., Sajassi, A., and Matsushima, S.,
"Inter-Chassis Communication Protocol for L2VPN PE
Redundancy", draft-ietf-pwe3-iccp-13 (work in progress),
January 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6870] Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", RFC 6870, February 2013.
10.2. Informative references
[I-D.ietf-l2vpn-vpls-mcast]
Aggarwal, R., Rekhter, Y., Kamite, Y., and L. Fang,
"Multicast in VPLS", draft-ietf-l2vpn-vpls-mcast-16 (work
in progress), November 2013.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
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[RFC6074] Rosen, E., Davie, B., Radoaca, V., and W. Luo,
"Provisioning, Auto-Discovery, and Signaling in Layer 2
Virtual Private Networks (L2VPNs)", RFC 6074,
January 2011.
[RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", RFC 6718, August 2012.
Authors' Addresses
Zhihua Liu
China Telecom
109 Zhongshan Ave.
Guangzhou 510630
P.R.China
Email: zhliu@gsta.com
Lizhong Jin
Shanghai
P.R.China
Email: lizho.jin@gmail.com
Ran Chen
ZTE Corporation
NO.19 East Huayuan Road
Haidian District Beijing 100191
P.R.China
Email: chen.ran@zte.com.cn
Dennis Cai
Cisco
3750 Cisco Way,
San Jose, California 95134
USA
Email: dcai@cisco.com
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Samer Salam
Cisco
595 Burrard Street, Suite:2123
Vancouver, BC V7X 1J1
Canada
Email: ssalam@cisco.com
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