AS_PATH length and route selection (WAS: Strange BGP announcement)

Wed Nov 18 01:46:50 UTC 1998

At 05:09 PM 11/17/98 -0800, Tony Li wrote:
>
>patrick at ianai.net (I Am Not An Isp) writes:
>
>> You said you wanted routers that followed the RFC.  The RFC does not
>> mention list AS_PATH length as a route selection criteria.  I have been
>> told that the draft for the next rev specifically prohibits using AS_PATH
>> length as a route selection criteria.
>
>
>Patently false.  In particular, the spec allows an implementation to invoke
>local policy when computing the local preference of a route.  An
>implementation can reasonably incorporate the AS path length in its local
>preference calculations as part of its policy.

Guess that answers the question.  So the draft for the next version of BGP
does not list as-path length as a necessary criteria, but does leave the
door open for vendor implementations (much like the current standard).

This, of course, leads to many, many other questions (such as the
possibility routing loops caused by different local policies as was seen
with implementations of BGP4), but few of which are of a truly operational
issue.  So I will apologize for starting a thread based on mis-information
and go back to my cave.

>Tony

TTFN,
patrick

I Am Not An Isp
www.ianai.net
"Think of it as evolution in action." - Niven & Pournelle