1. An Update on BGP Support for 4-byte ASN
Enke Chen
February 2001

2. Summary of Protocol Extensions <draft-ietf-idr-as4bytes-00.txt>
“4-byte AS number capability” defined
Encode the AS number as 4 bytes in the AS_PATH and AGGREGATOR attributes when the capability is shared.
Two new attributes: NEW_AS_PATH, NEW_AGGREGATOR introduced
Both are optional and transitive.
Complete AS path info can be re-constructed
One 2-byte ASN reserved for transition

3. Transition A matter of software upgrade No flag day is required
Community-based filtering
4-byte ASN can not be encoded directly into a community as specified in RFC 1997.
Either encode the private AS number in community, or use extended community

4. Implementation Protocol Extensions AS-path Based Policy
capability advertisement, new attributes
construct as path from both attributes
AS-path Based Policy
1:100 as part of regular expression (if so used)
Community Based Policy
support of extended community is optional

5. Estimated Timeline Finalize protocol in 1Q’2001
Protocol spec in reasonable shape
Requested capability code, and attributes codes from IANA
Implementation/test in 2Q’2001
extended community is optional
estimated coding time: 2 weeks
interoperability testing
Initial deployment in 2001

6. Acknowledgements
Thanks to Yakov Rekhter for his effort and significant contributions toward the proposed 4-byte AS number solution.