Network Working Group J. Dong
Internet-Draft M. Chen
Intended status: Standards Track Huawei Technologies
Expires: January 5, 2012 K. Patel
Cisco Systems
July 4, 2011
BGP End-of-RIB Usage Extension and Negotiation
draft-dong-idr-end-of-rib-use-extension-00
Abstract
This document describes the use of BGP End-of-RIB marker in improving
BGP routing convergence during initial route exchange. A mechanism
to negotiate the extension of End-of-RIB usage is also specified.
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.
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This Internet-Draft will expire on January 5, 2012.
Copyright Notice
Copyright (c) 2011 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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. BGP Convergence Problem in Initial Route Exchange . . . . . . . 3
3. End-of-RIB Usage Extension . . . . . . . . . . . . . . . . . . 3
4. BGP End-of-RIB Capability . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
BGP Graceful Restart (GR) [RFC4724] defines an End-of-RIB marker to
convey routing convergence information during BGP restart. It is
also specified that the generation of such a marker upon completion
of the initial update would be useful for routing convergence in
general.
Currently most of BGP routers neither generate End-of-RIB marker upon
completion of initial route advertisement nor anticipate the arrival
of End-of-RIB from peers during initial route exchange. In addition,
for some BGP implementations receiving End-of-RIB marker in scenarios
other than BGP GR may be treated as an error.
This document describes the benefit of using BGP End-of-RIB marker to
inform completion of initial BGP route exchange. A mechanism to
negotiate the extension of End-of-RIB usage is also specified.
2. BGP Convergence Problem in Initial Route Exchange
When a BGP speaker establishes BGP sessions with multiple peers, the
initial route exchange begins. Normally whenever a route is received
from one of the peers, BGP path calculation would be executed and new
UPDATE message will be advertised to peers immediately. Since during
initial route exchange the BGP speaker may consecutively receive
different routes to the same prefixes from different peers, this
normal procedure may cause the BGP speaker execute the path
calculation for some prefixes for multiple times, and would further
result in advertising non-optimal routes before routing convergence.
Apparently this is a waste of processing resource and also impacts
routing convergence and stability of the network. Some optimization
has been proposed. One typical approach is to set a timer for
initial route exchange, and BGP speaker will not execute path
calculation and advertise routes to peers until that timer expires.
The disadvantage of this approach is value of the timer would be
critical for BGP convergence performance, and since the timer value
would be fixed once configured, it cannot guarantee best performance
and convergence time for different cases.
3. End-of-RIB Usage Extension
[RFC4724] defines the use of End-of-RIB marker in BGP Graceful
Restart scenario, and it also specifies that "generation of such a
marker upon completion of the initial update would be useful for
routing convergence in general, and thus the practice is
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recommended".
Actually End-of-RIB marker should be used as an individual feature
independent of whether BGP GR is enabled or not. One example is
[RFC4684] specifies the use of End-of-RIB for RT Membership
information advertisement.
Similar to the use in BGP Graceful Restart, End-of-RIB marker could
also be used to inform completion of initial route exchange. Thus
route calculation and further advertisement would be suspended until
End-of-RIB marker is received from all or a predefined portion of BGP
peers. In addition, a relative large timer could be used as a backup
trigger to ensure path calculation and advertisement would always be
executed within a predefined time range.
Although it is easy to understand the use of End-of-RIB in improving
initial routing convergence, such benefit may not be obtained
directly, as currently most of BGP routers neither generate End-of-
RIB marker upon completion of initial route advertisement nor
anticipate the arrival of End-of-RIB from peers during initial route
exchange. In addition, for some BGP implementations receiving End-
of-RIB marker in scenarios other than BGP GR may be treated as an
error. Thus to use End-of-RIB for initial route exchange scenario,
some negotiation between the sending and receiving BGP speaker would
be necessary.
4. BGP End-of-RIB Capability
A new BGP capability called End-of-RIB Capability is defined. The
Capability code for this capability is to be assigned. The
Capability length field is zero.
By advertising this capability to a peer, a BGP speaker conveys to
the peer that the speaker support advertising and receiving End-of-
RIB marker and the related procedures described in this document.
After capability negotiation, if both the peer speaker and local
speaker support this capability, then End-of-RIB marker MUST be sent
to peer after finishing initial route advertisement, and both
speakers MUST use the End-of-RIB marker received from peer as
notification of initial exchange completion and trigger of local
route processing and further advertisement. If any one of the
peering speakers does not support this extension, End-of-RIB MUST not
be used in initial route exchange scenario.
When End-of-RIB is used for initial exchange, a timer MAY also be
used to control the maximum initial delay of route processing and
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UPDATEs advertisement. The timer value SHOULD be configurable.
5. IANA Considerations
A new BGP capability - End-of-RIB Capability is defined in this
document. The Capability code needs to be assigned by the IANA.
6. Security Considerations
This document does not change the security properties of BGP.
7. Acknowledgements
The authors would like to thank John Scudder, Shunwan Zhuang, Qing
Zeng for their valuable comments and discussions to this document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
January 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
8.2. Informative References
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, November 2006.
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Authors' Addresses
Jie Dong
Huawei Technologies
Huawei Building, No.3 Xinxi Rd
Beijing, 100085
China
Email: jie.dong@huawei.com
Mach Chen
Huawei Technologies
Huawei Building, No.3 Xinxi Rd
Beijing, 100085
China
Email: mach.chen@huawei.com
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: keyupate@cisco.com
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