honoring AS-path prepend from a peer or customer?

Avi Freedman freedman at avi.netaxs.com
Fri Feb 19 01:53:09 UTC 1999

In article <99118.183518.5014 at avi.netaxs.com> you wrote:

: If a peer (or transit customer) prepends their own AS to
: their route announcements to you, do you ever strip off
: the excessive As'es? That is, do you always honor them
: in your announcements to your other customers (or peers)?

: I do understand that any operator has full control over
: deciding his own outbound policy, regardless of the
: AS path.

: I want to know what the industry practice is and whether
: I should stipulate in my next upstream agreement that
: they honor my prepends?

: Thanks.

Standard practice is to accept them, though you may need to tell
the peer or upstream what regexps to allow if they filter by as-path
as well as by prefix.  (Always a good idea...)

My side question is - what shipping routers will let you rewrite
AS-Paths by doing anything other than just prepending?  Just wondering
if any 7007-type horrors are lurking in the wings.  I believe Criscos,
Bays, and gated boxes can't do this (without BGP->IGP->BGP redistribution).


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