honoring AS-path prepend from a peer or customer?

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1

: 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).

Avi

2

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...)

  Yes, whenever I've set up customer/peer bgp sessions, I've
done it such that we only did prefix filtering, not any as-path
filtering, this allows them to prepend as they wish, just not advert
anything other than what we filtered them at.

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).

  I'm also interested. There have been vendor bugs that have tipped
off 7007, etc.. but I'm only really familar with one vendor that (might) be
able to do something like this.

  I would suspect that anyone not honoring your as-path prepending
would be doing as-path filtering.

  - Jared