Network Working Group Albert J. Tian
Internet Draft
Expiration Date: Aug 2006 Redback Networks
Feb 2006
Generation ID for LDP
draft-tian-ldp-gen-id-00.txt
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Abstract
This document proposed two optional Generation ID TLVs in LDP Hello
messages and in LDP Initialization messages to speed up LDP
convergence in certain scenarios.
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1. Introduction
Consider two LSRs, LSRa and LSRb, that have an LDP session
established between them. LSRa is playing an active role in the LDP
session establishment, while LSRb is playing a passive role. For
certain LDP implementations, it is possible for the passive LSR LSRb
to fail and recover before the Hello Hold Time expires on its LDP
neighbor LSRa. It is also possible for LSRb to fail in a way that it
could not properly shutdown the TCP connections.
In this scenario, the only way for the active LDP neighbor LSRa to
detect the failure of LSRb would be for the KeepAlive Time to expire
on LSRa. In normal LDP configurations, the KeepAlive Time is usually
configured on the order of minutes. Before the KeepAlive Time
expires, proper LDP convergence can not be initiated.
2. LDP Extension
To solve this problem, we propose two new optional TLVs, Hello
Generation ID TLV in LDP Hello messages, and Session Generation
Generation ID TLV in Initialization Messages. Both two TLVs have the
same format but with different types:
Optional Parameter Type Length Value
Hello Generation ID TBD 4 See below
Session Generation ID TBD 4 See below
Hello Generation ID TLV and Session Generation ID TLV specify a 4
octet unsigned generation ID that identifies an LDP instance.
3. Operation
3.1. Sending Generation ID
For each LSR, when its LDP instance is initialized, a 4 octet
Generation ID should be generated. The Generation ID should remain
the same for the life time of the LDP instance.
Whenever the LSR needs to send out LDP Hello messages, it should
include the Generation ID value in the Hello Generation TLV in the
Hello messages; whenever the LSR needs to send out LDP Initialization
messages, it should include the Generation ID value in the Session
Generation TLV in the Initialization messages.
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3.2. Receiving Generation ID
Whenever an LSR receives LDP Initialization message from another LSR
with optional Session Generation ID TLV, it may remember the
Generation ID for the neighbor.
Whenever an LSR receives an LDP Hello message from an LDP neighbor
with a Hello Generation ID that is different from the remembered
Session Generation ID received from the same neighbor, then the LSR
may choose to terminate the LDP session to that neighbor. A
Notification message may be generated before the termination of the
session with error code TBD that indicates a Generation ID mismatch.
4. Security Considerations
This document does not introduce any new security issues.
5. IANA Considerations
This document proposes two new optional TLVs in LDP Hello messages
and LDP Initialization messages. The types of the two TLVs need to be
assigned by IANA. The document also proposes a new LDP Notification
error code for Generation ID mismatch. The new error code also needs
to be assigned by IANA.
6. Acknowledgments
The author would like to thank Venkatesan Pradeep for his help.
7. References
[RFC3036] L. Andersson, P. Doolan, N. Feldman, A. Fredette, and B.
Thomas, "LDP Specification", RFC 3036, January 2001.
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8. Author Information
Albert J. Tian
Redback Networks, Inc.
350 Holger Way
San Jose, CA 95134
Email: tian@redback.com
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