To all, I am using AS prepending to favor one ISP over another, in a BGP multihomed/multiISP scenario. Why does the ISP receiving the prepends fail to add my network into their routing table? Is this a "feature" of BGP, or have I gone too far with 3 prepend statements. Thx Philip __________________________________ Yahoo! Messenger Show us what our next emoticon should look like. Join the fun. http://www.advision.webevents.yahoo.com/emoticontest
On Apr 8, 2005, at 10:28 AM, Philip Lavine wrote:
I am using AS prepending to favor one ISP over another, in a BGP multihomed/multiISP scenario. Why does the ISP receiving the prepends fail to add my network into their routing table? Is this a "feature" of BGP, or have I gone too far with 3 prepend statements.
If they are both transit providers, then they are broken. If they are peers, the second ISP is probably preferring the route it hears through your transit provider because there are fewer AS hops. -- TTFN, patrick
On Fri, 8 Apr 2005, Patrick W Gilmore wrote:
On Apr 8, 2005, at 10:28 AM, Philip Lavine wrote:
I am using AS prepending to favor one ISP over another, in a BGP multihomed/multiISP scenario. Why does the ISP receiving the prepends fail to add my network into their routing table? Is this a "feature" of BGP, or have I gone too far with 3 prepend statements.
If they are both transit providers, then they are broken.
I have found at least one major ISP did check the amount of prepends and did not accept the announcement if it did not match exactly what was coded in their as-path filter. They had to code special as-path filters that allowed an undetermined number of prepends so we could "play". Why not just ask your upstream ISP if they filter prepends? -Hank
If they are peers, the second ISP is probably preferring the route it hears through your transit provider because there are fewer AS hops.
On Fri, 8 Apr 2005, Philip Lavine wrote:
I am using AS prepending to favor one ISP over another, in a BGP multihomed/multiISP scenario. Why does the ISP receiving the prepends fail to add my network into their routing table? Is this a "feature" of BGP, or have I gone too far with 3 prepend statements.
Who's ASN are you prepending on your advertised routes? ---------------------------------------------------------------------- Jon Lewis | I route Senior Network Engineer | therefore you are Atlantic Net | _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
participants (4)
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Hank Nussbacher -
Jon Lewis -
Patrick W Gilmore -
Philip Lavine