IDR Z. Li
Internet-Draft China Mobile
Updates: 4271, 4360, 7153 (if approved) J. Dong
Intended status: Standards Track Huawei Technologies
Expires: January 7, 2017 July 6, 2016
Carry congestion status in BGP extended community
draft-li-idr-congestion-status-extended-community-01
Abstract
A new extended community is introduced in this document to carry the
link congestion status, especially for the exit link of one AS. It
is called congestion status extended community. This extended
community can be used by the BGP routers to steer the Internet-access
traffic among the exit links by deploying policy routing.
Status of This Memo
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This Internet-Draft will expire on January 7, 2017.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Congestion Status Extended Community . . . . . . . . . . . . 4
4. Application Considerations . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
typically the architecture of a large scale ISP's network is multi-
layered, as illustrated in Figure 1. The national backbone network
has its own AS, and each of the province or state network has a
specific AS. Backbone network connects all the province or state
networks together and has several exit links to access the Internet.
The province or state networks usually have direct exit links to the
Internet. The total bandwidth of the backbone exit links is usually
much bigger than that of the direct exit links in the province or
state networks. Thus, the Internet-access traffic is mainly
transported through the backbone exit links by deploying route
policies on the ASBR routers in the province or state networks. The
ASBR routers in the province or state networks, for example, prefer
the routes learned from the backbone by setting higher local
preference for those routes. However, when the backbone exit links
are congested due to traffic increasing or delay of the capacity
expansion, the ASBR routers in the province or state networks do not
know this, and still delivery Internet-access traffic to the
backbone. The customer experience deteriorates, the operator, in
turn, will receive more and more complaints for its bad network
performance. Then, the operator has to steer some Internet-access
traffic to the direct exit links in the province or state networks by
deploying route policy on the ASBR routers. This kind of policy
should be removed when the capacity expansion of the backbone exit
links is done. The ASBR routers do not know this again.
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+---------------------------------------------------------+
| |
| Internet |
| +----------+ +----------+ +----------+ |
+-| Router a |----------| Router b |---------| Router c |-+
+----------+ +----------+ +----------+
/ \ \ /
---/-----\-------------------\------------------/----------
| \ \ /ISP Network
| +----------+ +----------+ +----------+
| +-| Router 1 |----| Router 2 |----| Router 3 |-+
| | +----------+ +----------+ +----------+ |
| | |
| | BACKBONE |
| | AS B |
| | +----------+ +----------+ +----------+ |
| +-| Router L |----| Router M |----| Router N |-+
| +----------+ +----------+ +----------+
| / | \
| / | \
+----------+ +----------+ +----------+
+-| Router X |-+ +-| Router Y |-+ +-| Router Z |-+
| +----------+ | | +----------+ | | +----------+ |
| province X | | province Y | | province Z |
| AS X | | AS Y | | AS Z |
+--------------+ +--------------+ +--------------+
Figure 1: Typical architecture of a large scale ISP's network
This document introduces a new extended community [RFC4360] to
delivery 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 Internet-access traffic according to
the congestion status of the exit link. Router X in the above
figure, for example, can steer some Internet-access traffic to the
direct exit link when it knows the backbone exit link is congested.
On the other hand, when Router X knows the exit link of the backbone
is not congested anymore, it can steer all the Internet-access
traffic back to the backbone network. The introduced extended
community is called congestion status extended community.
Congestion status extended community is good not only to the ASBRs in
other AS, but also to the BGP peers within one AS. For instance,
Router M in backbone AS chooses Router 2 to transport the Internet-
access traffic by default, because the IGP cost from Router M to
Router 2 is smallest. When Router M receives congestion status
extended communities from Router 1,2,3, which indicate the
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utilization of the exit link of Router 1,2,3 is 90%, 70%, and 50%
respectively, it can choose Router 3 to transport some Internet-
access traffic using route policy.
2. Terminology
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. 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 number can be encoded
in the first two bytes of the Sender AS Number field defined below.
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 2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x02 | Sub-Type | Sender AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender AS Number (cont.) | Bandwidth | Utilization |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: 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.
0x06 is suggested.
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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. The generator MUST have 4-octct AS number.
The "Bandwidth" field is 1 octet. Its value is the bandwidth of
the exit link in unit of gbps (gigabits per second).
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.
4. Application Considerations
To avoid route osilation, the exit router SHOULD set a threshold.
Only when the utilization change reach the threshold, the exit router
generates BGP update message with congestion status extended
community. Implementations SHOULD further reduce the BGP update
messages trigered by link utilization change using the method
simillar 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 accrodingly.
To avoid traffic osilation, 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 point of
the whole network.
5. Security Considerations
This document only defines a new extended communities to carry the
congestion status of the exit link. So, this document itself does
not directly introduce security issues. The same security
considerations as for the BGP extended community [RFC4360] applies.
6. 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. 0x06
is suggested.
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7. Acknowledgments
Many thanks to Rudiger Volk for his review and comments to improve
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,
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>.
8.2. Informative References
[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>.
[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>.
Authors' Addresses
Zhenqiang Li
China Mobile
No.32 Xuanwumenxi Ave., Xicheng District
Beijing 100032
P.R. China
Email: li_zhenqiang@hotmail.com
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Jie Dong
Huawei Technologies
Huawei Campus, No.156 Beiqing Rd.
Beijing 100095
P.R. China
Email: jie.dong@huawei.com
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