Internet DRAFT - draft-liu-l2vpn-vpls-inter-domain-redundancy
draft-liu-l2vpn-vpls-inter-domain-redundancy
Networking Working Group Z. Liu
Internet-Draft China Telecom
Intended status: BCP L. Jin
Expires: January 3, 2013 R. Chen
ZTE
D. Cai
S. Salam
Cisco
July 2, 2012
Redundancy provisioning for VPLS Inter-domain
draft-liu-l2vpn-vpls-inter-domain-redundancy-04
Abstract
In many 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
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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 . . . . . 5
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 . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative references . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
In many VPLS deployment 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 domain.
The domain in this document refers to 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 using
Inter-AS Option A, where VLANs are used to hand-off the services
between the 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
interconnect: 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 aggregate-able. These two conditions cannot always be
guaranteed in live deployments. For instance, there are many
scenarios where the interconnect between the domains uses POS (Packet
over Sonet/SDH), 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
desired failover time characteristics. Furthermore, in certain
situations MP-BGP is not deployed for VPLS. The redundancy solution
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described in this draft reuses ICCP [I-D.ietf-pwe3-iccp] and PW
redundancy [I-D.ietf-pwe3-redundancy] 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
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.
The two PW redundancy modes defined in
[I-D.ietf-pwe3-redundancy-bit], namely independent mode and master/
slave mode, are applicable in this solution. In order to maintain
control plane separation between the two domains, the independent
mode is preferred by operators. While 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.
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 only two physical links between the two domains and PE3 is
physically connected with PE5, and PE4 is physically connected with
PE6.
+---------+ +---------+
+---+ | +-----+ | active PW1 | +-----+| +---+
|PE1|---|-| PE3 |-|-----------------------|--| PE5 ||----|PE7|
+---+\ |/+-----+ | | +-----+\ /+---+
| \ / | * | | * | |\ / |
| \| | |ICCP| |ICCP| | | \ |
| / \ | * | | * | |/ \ |
+---+/ |\+-----+ | | +-----+/ \+---+
|PE2|---|-| PE4 |-|-----------------------|--| PE6 ||----|PE8|
+---+ | +-----+ | standby PW2 | +-----+| +---+
| | | |
| | | |
| RG1 | | RG2 |
+---------+ +---------+
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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 the two domains and the 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
5. PW redundancy application procedure for inter-domain
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 the following section.
There are two PW redundancy modes defined in
[I-D.ietf-pwe3-redundancy-bit]: Independent mode and Master/Slave
mode. For the inter-domain four-PW scenario, it is required for the
PEs to ensure that the same mode is supported on the two ICCP peers
in the same RG.
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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 PEs 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 domain;
o PW redundancy mode: independent mode only;
o Protection architectures: 1:1 (1 standby, 1 active).
The switchover rules described in section 5.2 apply. Before
deploying this inter-domain VPLS, the operators MUST negotiate to
configure same PW high/low priority at the two PW end-points. E.g,
in figure 1, PE3 and PE5 MUST both have higher/lower priority than
PE4 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:
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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 5.2 apply. In this case,
the operator does 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 5.2.1.
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 domain;
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 [I-D.ietf-pwe3-redundancy-bit], 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 remote the 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
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 5.2, otherwise, it MUST ignore the
request.
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The node isolation failure and node failure is described in section
5.2.
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 the 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 the two
inter-domain PWs connect to the PE are DOWN, the ICCP peer PE in
the same RG would switchover as described in section 5.2..
The node isolation failure and node failure is described in section
5.2.
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.
8. Acknowledgements
The authors wish to acknowledge the contributions of Daniel Cohn and
Yubao Wang.
Daniel Cohn
Orckit-Corrigent
Email: danielc@orckit.com
Yubao Wang
ZTE Corporation
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Email: wang.yubao@zte.com.cn
9. References
9.1. Normative references
[I-D.ietf-pwe3-iccp]
Martini, L., Salam, S., Sajassi, A., Bocci, M.,
Matsushima, S., and T. Nadeau, "Inter-Chassis
Communication Protocol for L2VPN PE Redundancy",
draft-ietf-pwe3-iccp-05 (work in progress), April 2011.
[I-D.ietf-pwe3-redundancy-bit]
Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", draft-ietf-pwe3-redundancy-bit-07
(work in progress), May 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. 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-10 (work
in progress), February 2012.
[I-D.ietf-pwe3-redundancy]
Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", draft-ietf-pwe3-redundancy-09 (work in
progress), June 2012.
[RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
Le Roux, "LDP Capabilities", RFC 5561, July 2009.
[RFC6074] Rosen, E., Davie, B., Radoaca, V., and Luo, W.,
"Provisioning, Auto-Discovery, and Signaling in Layer 2
Virtual Private Networks (L2VPNs)", RFC 6074, January
2011.
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Authors' Addresses
Zhihua Liu
China Telecom
109 Zhongshan Ave.
Guangzhou 510630
P.R.China
Email: zhliu@gsta.com
Lizhong Jin
ZTE Corporation
889 Bibo Road
Shanghai 201203
P.R.China
Email: lizhong.jin@zte.com.cn
Ran Chen
ZTE Corporation
68 Zijinghua Road
Nanjing 210012
P.R.China
Email: chen.ran@zte.com.cn
Dennis Cai
Cisco
3750 Cisco Way,
San Jose, California 95134
USA
Email: dcai@cisco.com
Samer Salam
Cisco
595 Burrard Street, Suite 2123
Vancouver, BC V7X 1J1
Canada
Email: ssalam@cisco.com
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