Network Working Group Srihari R. Sangli
Internet Draft Procket Networks
Expiration Date: February 2002
Daniel Tappan
Cisco Systems
Yakov Rekhter
Juniper Networks
BGP Extended Communities Attribute
draft-ietf-idr-bgp-ext-communities-01.txt
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as ``work in progress.''
The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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2. Abstract
This document describes an extension to BGP [BGP-4] which may be used
to provide flexible control over the distribution of routing
information.
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3. Introduction
The Extended Community Attribute provides two important enhancements
over the existing BGP Community Attribute:
- It provides an extended range, ensuring that communities can be
assigned for a plethora of uses, without fear of overlap.
- The addition of a Type field provides structure for the
community space.
The addition of structure allows the usage of policy based on the
application for which the community value will be used. For example,
one can filter out all communities of a particular type, or allow
only certain values for a particular type of community. It also
allows one to specify whether a particular community is transitive or
non-transitive across Autonomous system boundary. Without structure,
this can only be accomplished by explicitly enumerating all community
values which will be denied or allowed and passed to BGP speakers in
neighboring ASes based on the transitive property.
4. BGP Extended Communities Attribute
The Extended Communities Attribute is a transitive optional BGP
attribute. The attribute consists of a set of "extended
communities". Each extended community is coded as an eight octet
value. All routes with the Extended Communities attribute belong to
the communities listed in the attribute.
The Extended Communities Attribute has Type Code 16.
Each Extended Community is encoded as an eight octet quantity, as
follows:
- Type Field : 1 or 2 octets
- Value Field : Remaining octets
Type Field:
Two classes of Type Field are introduced: Regular type and
Extended type.
The size of Type Field for Regular types is 1 octet and the
size of the Type Field for Extended types is 2 octets.
The value of the high-order octet will determine if its a
regular type or an extended type. The value of the high-order
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octet of the Type Field defined as regular type (or extended
type) for a extended community MUST NOT be reused as the value
of the high-order octet of the Type Field defined as extended
type (or regular type). In other words, a new extended
community of regular type (extended type) should have unique
(and new) value for the high-order octet (high-order and low-
order octet).
The high-order octet of the Type Field is as shown below:
First bit (MSB) : IANA authority bit
Value 0 : IANA assignable type
Value 1 : Vendor-specific types
Second bit : Transitive bit
Value 0 : The community is
Transitive across ASes
Value 1 : The community is
Non-Transitive across ASes
Remaining 6 bits : Indicates the structure of the
community
Value Field:
The encoding of the Value Field is dependent on the "type" of
the community as specified by the Type Field. The encoding of
the community for the transitive communities should be such
that it is unique globally (i.e. across the Autonomous
Systems).
Two extended communities are declared equal only when entire 8
octets are equal.
The two members in the tuple <Type, Value> should be enumerated to
specify any community value. Based on the value of the Type field,
the remaining octets of the community should be interpreted.
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5. New BGP Extended Community Types.
This document introduces a few extended types and defines the Value
Field for those types.
Type 0x00:
This is an extended type with Type Field comprising of 2 octets
and Value Field comprising of 6 octets.
The value of the high-order octet of this extended type is
0x00. The low-order octet of this extended type is used to
indicate sub-types.
The Value Field consists of two sub-fields:
Global Administrator sub-field: 2 octets
This sub-field contains an Autonomous System number
assigned by IANA.
Local Administrator sub-field: 4 octets
The organization identified by Autonomous System number
in the Global Administrator sub-field, can encode any
information in this sub-field. The value and meaning of
the value encoded in this sub-field should be defined by
the sub-type of the community.
Type 0x01:
This is an extended type with Type Field comprising of 2 octets
and Value Field comprising of 6 octets.
The value of the high-order octet of this extended type is
0x01. The low-order octet of this extended type is used to
indicate sub-types.
The Value field consists of two sub-fields.
Global Administrator sub-field: 4 octets
This sub-field contains an IPv4 address assigned by IANA.
Local Administrator sub-field: 2 octets
The organization which has been assigned the IPv4 address
in the Global Administrator sub-field, can encode any
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information in this sub-field. The value and meaning of
this value encoded in this sub-field should be defined by
the sub-type of the community.
Type 0x02:
This is an extended type with Type Field comprising of 2 octets
and Value Field comprising of 6 octets.
The value of the high-order octet of this extended type is
0x02. The low-order octet of this extended type is used to
indicate sub-types.
The Value Field consists of two sub-fields.
Global Administrator sub-field: 4 octets
This sub-field contains a 4-octets Autonomous System
number assigned by IANA.
Local Administrator sub-field: 2 octets
The organization identified by Autonomous System number
in the Global Administrator sub-field, can encode any
information in this sub-field. The value and meaning of
the value encoded in this sub-field should be defined by
the sub-type of the community.
6. Route Target Community
The Route Target Community identifies one or more routers that may
receive a set of routes (that carry this Community) carried by BGP.
This is transitive across the Autonomous system boundary.
The value of the Type field for the Route Target Community is 0x00 or
0x01. The value of the low-order octet of the extended type field
for this community is 0x02.
When the value of the Type field is 0x00, the value of the Local
Administrator sub-field in the Value Field MUST be unique within the
Autonomous system carried in the Global Administrator sub-field.
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7. Route Origin Community
The Route Origin Community identifies one or more routers that inject
a set of routes (that carry this Community) into BGP. This is
transitive across the Autonomous system boundary.
The value of the Type field for the Route Origin Community is 0x00 or
0x01. The value of the low-order octet of the extended type field
for this community is 0x03.
When the value of the Type field is 0x00, the value of the Local
Administrator sub-field in the Value Field MUST be unique within the
Autonomous system carried in the Global Administrator sub-field.
8. Link Bandwidth Community
When a router receives a route from a directly connected external
neighbor (the external neighbor that is one IP hop away), and
advertises this route (via IBGP) to internal neighbors, as part of
this advertisement the router may carry the bandwidth of the link
that connects the router with the external neighbor. The bandwidth of
such a link is carried in the Link Bandwidth Community. The community
is non-transitive across the Autonomous system boundary.
The value of the high-order octet of the extended Type Field is 0x40.
The value of the low-order octet of the extended type field for this
community is 0x04.
The value of the Global Administrator sub-field in the Value Field
MUST represent the Autonomous System of the router that attaches the
Link Bandwidth Community. When a router receives a route with the
community, the router may check the AS number in the Global
Administrator sub-field to see if its not the local AS and hence
ignore the information carried in the Link Bandwidth Community.
The bandwidth of the link is expressed as 4 octets in IEEE floating
point format, units being bytes per second. It is carried in the
Local Administrator sub-field of the Value Field.
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9. Operations
A BGP speaker may use the Extended Communities attribute to control
which routing information it accepts, prefers or distributes to its
peers.
A BGP speaker receiving a route that doesn't have the Extended
Communities attribute may append this attribute to the route when
propagating it to its peers.
A BGP speaker receiving a route with the Extended Communities
attribute may modify this attribute according to the local policy.
A BGP speaker should not propagate a non-transitive extended
community across the Autonomous system boundary.
A route may carry both the BGP Communities attribute as defined in
[RFC1997]), and the Extended BGP Communities attribute. In this case
the BGP Communities attribute is handled as specified in [RFC1997],
and the Extended BGP Communities attribute is handled as specified in
this document.
10. IANA Considerations
For the high-order octet of the Type Field, values 0x00 through 0x02
are assigned in this document and are defined as extended types. For
the low-order octet of the Type Field, values 0x02 through 0x04 are
assigned in this document.
The Type Field values 0x03-0x3f for regular types (0x0300-0x3fff when
expressed as extended types) are to be assigned by IANA, using the
"First Come First Served" policy defined in RFC 2434. The extended
type field values 0x0005-0x00ff, 0x0104-0x01ff and 0x0200-0x02ff are
to be assigned by IANA, using the "First Come First Served" policy
defined in RFC 2434. Type values 0x80-0xbf for regular types
(0x8000-0xbfff when expressed as extended types) are for vendor-
specific types, and values in this range are not to be assigned by
IANA.
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11. Security Considerations
This extension to BGP does not change the underlying security issues.
12. Acknowledgements
The authors would like to thank John Hawkinson, Jeffrey Haas for
their feedback.
13. References
[BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
(BGP-4)", RFC 1771, March 1995.
[RFC1997] Chandra, R., Traina, P., Li, T., "BGP Communities
Attribute", RFC1997, August 1996.
14. Author Information
Srihari R. Sangli
Procket Networks, Inc.
1100 Cadillac Court
Milpitas, CA - 95035
e-mail: srihari@procket.com
Dan Tappan
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
e-mail: tappan@cisco.com
Yakov Rekhter
Juniper Networks, Inc.
1194 N. Mathilda Ave
Sunnyvale, CA 94089
e-mail: yakov@juniper.net
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