IDR Z. Li
Internet-Draft China Mobile
Updates: 4271, 4360, 7153 (if approved) J. Dong
Intended status: Experimental Huawei Technologies
Expires: January 1, 2018 June 30, 2017
Carry congestion status in BGP extended community
draft-li-idr-congestion-status-extended-community-05
Abstract
A new extended community, called congestion status extended
community, is introduced in this document to carry the link
congestion status, especially for the exit link of one AS.
Congestion status extended community can be used by the BGP speakers
to steer the AS-outgoing traffic among the exit links.
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 [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
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This Internet-Draft will expire on January 1, 2018.
Copyright Notice
Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Congestion Status Extended Community . . . . . . . . . . . . 4
3. Application Considerations . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Knowing the congestion status of the AS exit links is useful for
traffic steering, especially for steering the AS outgoing traffic
among the exit links.
AS A, as shown in the following figure, has multiple exit links
connected to AS B. Both AS A and B has exit link to AS C, and AS B
provides transit service for AS A. Due to cost or some other
reasons, AS A prefers using AS B to transmit its' traffic to AS C,
not the directly connected link between AS A and C. If the exit
routers, Router 7 and 8, in AS A tell their iBGP peers the congestion
status of the exit links, the peers in turn can steer some outgoing
traffic toward the less loaded exit link. If AS A knows the link
between AS B and AS C is congested, it can steer some traffic towards
AS C from AS B to the directly connected link by applying some route
policies.
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+-------------------------------------------+
| AS C |
| +----------+ +----------+ |
+--| Router 1 |---------------| Router 2 |--+
+----------+ +----------+
| |
| |
| +----------+
| +--------| Router 3 |----------+
| | +----------+ |
| | AS B |
| | +----------+ +----------+ |
| +-| Router 4 |----| Router 5 |-+
| +----------+ +----------+
| | |
| | |
+----------+ +----------+ +----------+
+--| Router 6 |--------| Router 7 |----| Router 8 |-+
| +----------+ +----------+ +----------+ |
| AS A |
+---------------------------------------------------+
In [constrained-multiple-path], authors from France Telecom also
specified the requirement to know the congestion status of a link.
This document introduces a new extended community [RFC4360] to
deliver the congestion status of the exit link to other BGP speakers.
The BGP receiver can then use this extended community to deploy route
policy, thus steer AS outgoing traffic according to the congestion
status of the exit links. This mechanisum can be used by both iBGP
and eBGP.
In a network deployed SDN (Software Defined Network) controller,
congestion status extended community can be used by the controller to
steer the AS outgoing traffic among all the exit links from the
perspective of the whole network.
For the network with Route Reflectors (RRs) [RFC4456], RRs by default
only advertise the best route for a specific prefix to their clients.
Thus RR clients has no opportunity to compare the congestion status
among all the exit links. In this situation, to allow RR clients
learning all the routes for a specific prefix from all the exit
links, RRs are RECOMMENDED to enable add-path functionality
[RFC7911].
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2. Congestion Status Extended Community
As described in [RFC4360], the extended community attribute is an
8-octet value with the first one or two octets to indicate the type
of this attribute. Since congestion status extended community needs
to be delivered from on AS to other ASes, and used by the BGP
speakers both in other ASes and within the same AS as the sender, it
MUST be a transitive extended community, i.e. the T bit in the first
octet MUST be zero.
We only define the congestion status extended community for four-
octet AS number [RFC6793], since all the BGP speakers can handle
four-octet AS number now and the two-octet AS numbers can be mapped
to four-octet AS numbers by setting the two high-order octets of the
four-octet field to zero, as per [RFC6793].
Congestion status extended community is a sub-type allocated from
Transitive Four-Octet AS-Specific Extended Community Sub-Types
defined in section 5.2.4 of [RFC7153]. Its format is as Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type =0x02 | Sub-Type | Sender AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender AS Number (cont.) | Bandwidth | Utilization |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Congestion status extended community
The "Type" field MUST be 0x02, which indicate this is a Transitive
Four-Octet AS-Specific Extended Community.
The "Sub-Type" field is used to indicate this is a Congestion
Status Extended Community. Its value is to be assigned by IANA.
The "Sender AS Number" field is 4 octets. Its value is the AS
number of the BGP speaker who generates this congestion status
extended community. If the generator has 2-octct AS number, it
MUST encode its AS number in the last (low order) two bytes and
set the first (high order) two bytes to zero, as per [RFC6793].
The "Bandwidth" field is 1 octet. Its value is the bandwidth of
the exit link in unit of 10 gbps (gigabits per second). The link
with bandwidth less than 10 gbps is not suitable to use this
feature.
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The "Utilization" field is 1 octet. Its value is the utilization
of the exit link in unit of percent. We can use the "Utilization"
field together with the "Bandwidth" field to calculate the traffic
load that we can further steer to this exit link.
3. Application Considerations
To avoid route oscillation, the exit router SHOULD set a threshold.
When the utilization change reaches the threshold, the exit router
SHOULD generate a BGP update message with congestion status extended
community. Implementations SHOULD further reduce the BGP update
messages trigered by link utilization change using the method similar
to BGP Route Flap Damping [RFC2439]. When link utilization change by
small amounts that fall under thresholds that would cause the
announcement of BGP update message, implementations SHOULD suppress
the announcement and set the penalty value accordingly.
To avoid traffic oscillation, i.e. more traffic than expected is
attracted to the low utilized link, and some traffic has to be
steered back to other links, route policy can be set at the exit
router. Congestion status extended community is only conveyed for
some specific routes or only for some specific BGP peers. Congestion
status extended community can also be used in a SDN network. The SDN
controller uses the exit link utilization information to steer the
Internet access traffic among all the exit links from the perspective
of the whole network.
4. Security Considerations
This document only defines a new extended communities to carry the
congestion status of the exit link. This new extended community does
not directly introduce any new security issues. The same security
considerations as for the BGP extended community [RFC4360] applies.
5. IANA Considerations
One sub-type is solicited to be assigned from Transitive Four-Octet
AS-Specific Extended Community Sub-Types registry to indicate the
Congestion Status Extended Community defined in this document.
6. Acknowledgments
Many thanks to Rudiger Volk, Susan Hares, John Scudder, Randy Bush
for their review and comments to improve this document.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
[RFC7153] Rosen, E. and Y. Rekhter, "IANA Registries for BGP
Extended Communities", RFC 7153, DOI 10.17487/RFC7153,
March 2014, <http://www.rfc-editor.org/info/rfc7153>.
7.2. Informative References
[constrained-multiple-path]
Boucadair, M. and C. Jacquenet, "Constrained Multiple BGP
Paths", October 2010.
[RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
Flap Damping", RFC 2439, DOI 10.17487/RFC2439, November
1998, <http://www.rfc-editor.org/info/rfc2439>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<http://www.rfc-editor.org/info/rfc4456>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<http://www.rfc-editor.org/info/rfc6793>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<http://www.rfc-editor.org/info/rfc7911>.
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Authors' Addresses
Zhenqiang Li
China Mobile
No.32 Xuanwumenxi Ave., Xicheng District
Beijing 100032
P.R. China
Email: li_zhenqiang@hotmail.com
Jie Dong
Huawei Technologies
Huawei Campus, No.156 Beiqing Rd.
Beijing 100095
P.R. China
Email: jie.dong@huawei.com
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