draft-ietf-idr-as4bytes-00.txt   draft-ietf-idr-as4bytes-01.txt 
Network Working Group Quaizar Vohra Network Working Group Quaizar Vohra
Internet Draft Juniper Networks Internet Draft Juniper Networks
Expiration Date: July 2001 Enke Chen Expiration Date: August 2001 Enke Chen
Network Working Group Redback Networks, Inc. Network Working Group Redback Networks, Inc.
BGP support for four-octet AS number space BGP support for four-octet AS number space
draft-ietf-idr-as4bytes-00.txt draft-ietf-idr-as4bytes-01.txt
1. Status of this Memo 1. Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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material or to cite them other than as ``work in progress.'' material or to cite them other than as ``work in progress.''
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
2. Abstract 2. Abstract
Currently the Autonomous System number is encoded in BGP as a two- Currently the Autonomous System number is encoded in BGP [BGP] as a
octets field. This document describes extensions to BGP to carry the two-octets field. This document describes extensions to BGP to carry
Autonomous System number as a four-octets field. the Autonomous System number as a four-octets field.
3. Protocol Extensions 3. Protocol Extensions
For the purpose of this document lets define a BGP speaker which For the purpose of this document lets define a BGP speaker which
doesn't support the new 4-octets AS number extensions as an OLD BGP doesn't support the new 4-octets AS number extensions as an OLD BGP
speaker, and a BGP speaker which supports the new 4-octets AS number speaker, and a BGP speaker which supports the new 4-octets AS number
extensions as a NEW BGP speaker. extensions as a NEW BGP speaker.
BGP carries the Autonomous System number in the My Autonomous System BGP carries the Autonomous System number in the My Autonomous System
field of the OPEN message, in the AS_PATH attribute of the UPDATE field of the OPEN message, in the AS_PATH attribute of the UPDATE
message, and in the AGGREGATOR attribute of the UPDATE message. BGP message, and in the AGGREGATOR attribute of the UPDATE message. BGP
also carries the Autonomous System number in the BGP Communities also carries the Autonomous System number in the BGP Communities
attribute. attribute.
A NEW BGP speaker uses BGP Capability Advertisements [BGP-CAP] to A NEW BGP speaker uses BGP Capability Advertisements [RFC2842] to
advertise to its neighbors (either internal or external) that it advertise to its neighbors (either internal or external) that it
supports 4-octets AS number extensions, as specified in this supports 4-octets AS number extensions, as specified in this
document. The BGP Capability code for this capability is [TBD]. document. The BGP Capability code for this capability is [TBD].
The Capability that is used by a BGP speaker to convey to its BGP The Capability that is used by a BGP speaker to convey to its BGP
peer the 4-octets Autonomous System number capability, also carries peer the 4-octets Autonomous System number capability, also carries
the 4-octets Autonomous System number of the speaker in the the 4-octets Autonomous System number of the speaker in the
Capability Value field of the Capability Optional Parameter. The Capability Value field of the Capability Optional Parameter. The
Capability Length field of the Capability is set to 4. Capability Length field of the Capability is set to 4.
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entity. entity.
To preserve AS path information with 4-octets AS numbers across OLD To preserve AS path information with 4-octets AS numbers across OLD
BGP speakers, this document defines a new AS path attribute, called BGP speakers, this document defines a new AS path attribute, called
NEW_AS_PATH. This attribute is optional transitive and contains the NEW_AS_PATH. This attribute is optional transitive and contains the
AS path encoded with 4-octets AS numbers. The NEW_AS_PATH attribute AS path encoded with 4-octets AS numbers. The NEW_AS_PATH attribute
has the same semantics as the AS_PATH attribute, except that it is has the same semantics as the AS_PATH attribute, except that it is
optional transitive, and it carries 4-octets AS numbers. The Type optional transitive, and it carries 4-octets AS numbers. The Type
Code for this attribute is <TBD> Code for this attribute is <TBD>
To prevent the possible propagation of confederation path segments
outside of a confederation, the path segment types AS_CONFED_SEQUENCE
and AS_CONFED_SET [RFC3065] are declared invalid for the NEW_AS_PATH
attribute.
Similarly, this document defines a new aggregator attribute called Similarly, this document defines a new aggregator attribute called
NEW_AGGREGATOR, which is optional transitive. The NEW_AGGREGATOR NEW_AGGREGATOR, which is optional transitive. The NEW_AGGREGATOR
attribute has the same semantics as the AGGREGATOR attribute, except attribute has the same semantics as the AGGREGATOR attribute, except
that it carries 4-octets AS numbers. The Type Code for this attribute that it carries 4-octets AS numbers. The Type Code for this attribute
is <TBD>. is <TBD>.
Currently assigned 2-octets Autonomous System numbers are converted Currently assigned 2-octets Autonomous System numbers are converted
into 4-octets Autonomous System numbers by setting the high-order 2 into 4-octets Autonomous System numbers by setting the high-order 2
octets of the 4-octets field to zero. Such a 4-octets AS number is octets of the 4-octets field to zero. Such a 4-octets AS number is
said to be mappable to a 2-octets AS number. said to be mappable to a 2-octets AS number.
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composed of 2-octets AS numbers only. In this case the NEW speaker composed of 2-octets AS numbers only. In this case the NEW speaker
should not send the NEW_AS_PATH attribute. should not send the NEW_AS_PATH attribute.
In the AS_PATH attribute encoded with 2-octets AS numbers, non- In the AS_PATH attribute encoded with 2-octets AS numbers, non-
mappable 4-octets AS numbers are represented by the well known mappable 4-octets AS numbers are represented by the well known
2-octets AS number, AS_TRANS. This will preserve the path length 2-octets AS number, AS_TRANS. This will preserve the path length
property of the AS path information; and will also help in updating property of the AS path information; and will also help in updating
the AS path information received on a NEW BGP speaker from an OLD the AS path information received on a NEW BGP speaker from an OLD
speaker, as explained in the next section. speaker, as explained in the next section.
The NEW speaker constructs the NEW_AS_PATH attribute from the AS_PATH Except for the case where the AS_PATH attribute contains either
attribute by taking the attribute length and attribute value from the AS_CONFED_SEQUENCE or AS_CONFED_SET path segment, the NEW speaker
AS_PATH attribute and placing them into the attribute length and constructs the NEW_AS_PATH attribute from the AS_PATH attribute by
attribute value of the NEW_AS_PATH attribute. The NEW_AS_PATH taking the attribute length and attribute value from the AS_PATH
attribute will be carried across a series of OLD BGP speakers without attribute and placing them into the attribute length and attribute
modification and will help preserve the truely 4-octets AS numbers in value of the NEW_AS_PATH attribute. In the case where the AS_PATH
the AS path information. attribute contains either AS_CONFED_SEQUENCE or AS_CONFED_SET path
segments, the NEW speaker, when copying information from the AS_PATH
attribute into the NEW_AS_PATH attribute, must exclude such path
segments from copying. The NEW_AS_PATH attribute will be carried
across a series of OLD BGP speakers without modification and will
help preserve the truely 4-octets AS numbers in the AS path
information.
Similarly, if the NEW speaker has to send the AGGREGATOR attribute, Similarly, if the NEW speaker has to send the AGGREGATOR attribute,
and if the aggregating Autonomous System's AS number is truely and if the aggregating Autonomous System's AS number is truely
4-octets, the speaker constructs the NEW_AGGREGATOR attributes by 4-octets, the speaker constructs the NEW_AGGREGATOR attributes by
taking the attribute length and attribute value from the AGGREGATOR taking the attribute length and attribute value from the AGGREGATOR
attribute and placing them into the attribute length and attribute attribute and placing them into the attribute length and attribute
value of the NEW_AGGREGATOR attribute, and sets the AS number field value of the NEW_AGGREGATOR attribute, and sets the AS number field
in the existing AGGREGATOR attribute to the reserved AS number, in the existing AGGREGATOR attribute to the reserved AS number,
AS_TRANS. Note that if the AS number is 2-octets only, then the AS_TRANS. Note that if the AS number is 2-octets only, then the
NEW_AGGREGATE attribute should not be sent. NEW_AGGREGATE attribute should not be sent.
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Autonomous system or one router at a time. Autonomous system or one router at a time.
To simplify transition this document assumes that an Autonomous To simplify transition this document assumes that an Autonomous
System could start using 4-octets AS number only after all the BGP System could start using 4-octets AS number only after all the BGP
speakers within that Autonomous System have been upgraded to support speakers within that Autonomous System have been upgraded to support
4-octets AS numbers. 4-octets AS numbers.
An OLD BGP speaker should not use AS_TRANS as its Autonomous System An OLD BGP speaker should not use AS_TRANS as its Autonomous System
number. number.
A non-mappable 4-octets AS number can not be used as a "Member AS
Number" of a BGP Confederation until all the BGP speakers within the
Confederation transitioned to support 4-octets AS numbers.
In an environment where an Autonomous System that has OLD BGP In an environment where an Autonomous System that has OLD BGP
speakers peers with two or more Autonomous Systems that have NEW BGP speakers peers with two or more Autonomous Systems that have NEW BGP
speakers and use AS_TRANS (rather than having a globally unique AS speakers and use AS_TRANS (rather than having a globally unique AS
number), use of Multi-Exit Discriminators by the Autonomous System number), use of Multi-Exit Discriminators by the Autonomous System
with the OLD speakers may result in a situation where Multi-Exit with the OLD speakers may result in a situation where Multi-Exit
Discriminator will influence route selection among the routes that Discriminator will influence route selection among the routes that
were received from different neighboring Autonomous Systems. were received from different neighboring Autonomous Systems.
Under certain conditions it may not be possible to reconstruct the Under certain conditions it may not be possible to reconstruct the
entire AS path information from the AS_PATH and the NEW_AS_PATH entire AS path information from the AS_PATH and the NEW_AS_PATH
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Security issues are not discussed in this document. Security issues are not discussed in this document.
8. Acknowledgments 8. Acknowledgments
The authors would like to thank Yakov Rekhter and Chaitanya The authors would like to thank Yakov Rekhter and Chaitanya
Kodeboyina for the numerous discussions which went into the making of Kodeboyina for the numerous discussions which went into the making of
this draft. this draft.
9. References 9. References
[BGP-CAP] Chandra, R., and Scudder, J., "Capabilities Advertisement [BGP] Rekhter, Y., Li, T., "Border Gateway Protocol 4", draft-ietf-
with BGP-4", RFC 2842, May 2000. idr-bgp4-12.txt
[EXT-COM] Ramachandra, S., Tappan, D., and Rekter Y. "BGP Extended [EXT-COM] Ramachandra, S., Tappan, D., and Rekter Y. "BGP Extended
Communities Attribute", draft-ramachandra-bgp-ext-communities-02.txt Communities Attribute", draft-ramachandra-bgp-ext-communities-02.txt
[RFC1997] Chandra, R., Traina, P. and T. Li, "BGP Communities [RFC1997] Chandra, R., Traina, P. and T. Li, "BGP Communities
Attribute", RFC 1997, August 1996. Attribute", RFC 1997, August 1996.
[RFC2842] Chandra, R., and Scudder, J., "Capabilities Advertisement
with BGP-4", RFC 2842, May 2000.
[RFC3065] Traina, P., McPherson, D., Scudder, J., "Autonomous System
Confederations for BGP", RFC3065, February 2001.
10. Author Information 10. Author Information
Quaizar Vohra Quaizar Vohra
Juniper Networks Juniper Networks
1194 N.Mathilda Ave 1194 N.Mathilda Ave
Sunnyvale, CA 94089 Sunnyvale, CA 94089
e-mail: qv@juniper.net e-mail: qv@juniper.net
Enke Chen Enke Chen
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