Network Working Group Q. Zeng
Internet-Draft J. Dong
Intended status: Standards Track Huawei Technologies
Expires: January 5, 2012 July 4, 2011
Maximum Transmission Unit Extended Community for BGP-4
draft-zeng-idr-bgp-mtu-extension-00
Abstract
Proper functioning of [RFC1191] path Maximum Transmission Unit (MTU)
discovery requires that IP routers have knowledge of the MTU for each
link to which they are connected. As MPLS progresses, [RFC3988]
specifies some extensions to LDP in support of LDP LSP MTU discovery.
For the LSP created using Border Gateway Protocol (BGP) [RFC3107], it
does not have the ability to signal the path MTU to the ingress Label
Switching Router (LSR). In the absence of this functionality, the
MTU for the BGP LSP must be statically configured by network
operators or by equivalent off-line mechanisms.
This document defines the MTU Extended Community for BGP in support
of BGP LSP MTU discovery.
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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 5, 2012.
Copyright Notice
Zeng & Dong Expires January 5, 2012 [Page 1]
Internet-Draft MTU Extended Community for BGP-4 July 2011
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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. BGP LSP MTU Discovery . . . . . . . . . . . . . . . . . . . . . 3
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. MTU Extended Community . . . . . . . . . . . . . . . . . . 3
2.3. Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Applicability Considerations . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Zeng & Dong Expires January 5, 2012 [Page 2]
Internet-Draft MTU Extended Community for BGP-4 July 2011
1. Introduction
Proper functioning of [RFC1191] path Maximum Transmission Unit (MTU)
discovery requires that IP routers have knowledge of the MTU for each
link to which they are connected. As MPLS progresses, [RFC3988]
specifies some extensions to LDP in support of LDP LSP MTU discovery.
For the LSP created using Border Gateway Protocol (BGP) [RFC3107], it
does not have the ability to signal the path MTU to the ingress Label
Switching Router (LSR). Without knowledge of the path MTU of the
whole BGP LSP, ingress BGP LSRs may transmit packets along that LSP
which are either too big or too small, thus these packets may be
silently discarded by LSRs or inefficient transmitted. In the
absence of this functionality, the MTU for each BGP LSP must be
statically configured by network operators or by equivalent off-line
mechanisms.
This document defines the MTU Extended Community for BGP in support
of BGP LSP MTU discovery.
2. BGP LSP MTU Discovery
2.1. Definitions
BGP LSP Path MTU: The Path MTU of the LSP from given BGP LSR to a
specific prefix. It is carried as a Extended Community with the BGP
labeled IPv4 (or IPv6) route.
BGP LSR Link MTU: If the two BGP LSRs are directly adjacent, the BGP
LSR Link MTU is the MTU of the interface; If the two BGP LSRs are not
directly adjacent, the BGP LSR Link MTU is the Path MTU of the
underlying tunnel. If there are multiple links between the two BGP
LSRs, the BGP LSR Link MTU is the minimum of those link MTUs.
2.2. MTU Extended Community
BGP LSP Path MTU is carried in the MTU extended community for BGP-4.
The MTU extended community is an optional transitive attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU extended community Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | MTU Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The MTU extended community type is to be assigned by IANA. The first
four octets of the value field should be reserved, and the MTU value
Zeng & Dong Expires January 5, 2012 [Page 3]
Internet-Draft MTU Extended Community for BGP-4 July 2011
is carried in the following two octets of the value field.
2.3. Signaling
The MTU is advertised hop-by-hop from BGP egress LSR to BGP ingress
LSR along an BGP LSP. The steps are as follows:
A. If BGP speaker A is originator of the labeled IPv4 (or IPv6)
route, A sets its BGP LSP Path MTU to the maximal value, advertises
the labeled IPv4 (or IPv6) route with the MTU Extended Community to
its BGP Peer (its upstream BGP LSR).
B. BGP speaker B receives the labeled IPv4 (or IPv6) route with BGP
LSP Path MTU from its BGP peer.
a) B SHOULD computes the BGP LSR Link MTU to the Next Hop of the
received message, then sets its BGP LSP Path MTU to the minimum of
the received BGP LSP Path MTU and the BGP LSR Link MTU.
b). If B distributes the route with the Next Hop attribute
unchanged, it MUST keep the MTU Extended Community unchanged when
advertising the message to its upstream BGP LSRs.
c). If B would change the Next Hop attribute to itself in the
subsequent advertisement, it SHOULD set the MTU Extended Community in
the message with its BGP LSP Path MTU obtained through step (a).
3. Applicability Considerations
The BGP MTU Extended Community is applicable to the BGP LSP defined
in [RFC3107].
4. IANA Considerations
IANA is requested to assign a type and sub-type value for BGP MTU
extended community.
5. Security Considerations
This extension to BGP does not change the underlying security issues
in [RFC4271].
Zeng & Dong Expires January 5, 2012 [Page 4]
Internet-Draft MTU Extended Community for BGP-4 July 2011
6. Contributors
The following individuals contributed to this document:
Haibo Wang
Haijun Xu
7. Acknowledgements
TBD
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.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in
BGP-4", RFC 3107, May 2001.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
8.2. Informative References
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[RFC3988] Black, B. and K. Kompella, "Maximum Transmission Unit
Signalling Extensions for the Label Distribution
Protocol", RFC 3988, January 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
"BGP-MPLS IP Virtual Private Network (VPN) Extension for
IPv6 VPN", RFC 4659, September 2006.
Zeng & Dong Expires January 5, 2012 [Page 5]
Internet-Draft MTU Extended Community for BGP-4 July 2011
Authors' Addresses
Qing Zeng
Huawei Technologies
Huawei Building, No.3 Xinxi Rd
Beijing 100085
China
Email: zengqing@huawei.com
Jie Dong
Huawei Technologies
Huawei Building, No.3 Xinxi Rd
Beijing 100085
China
Email: jie.dong@huawei.com
Zeng & Dong Expires January 5, 2012 [Page 6]