Update: I am prepending my AS 3 times to the un-preferred ISP. Both ISP's are my peers. The un-preferred ISP claims the see my advertisement yet they do not add it to their routing table (suggests filtering??). They claim all the filtering they are doing is based on the networks I told them over the phone that I was using with that AS. Philip --- Jon Lewis <jlewis@lewis.org> wrote:
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?
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I am prepending my AS 3 times to the un-preferred ISP. Both ISP's are my peers. The un-preferred ISP claims the see my advertisement yet they do not add it to their routing table (suggests filtering??). They claim all the filtering they are doing is based on the networks I told them over the phone that I was using with that AS. To answer your originial question: it is not "normal" to filter routers with
On Friday 08 April 2005 16:04, Philip Lavine wrote: the same AS prepended 3 times. However if the ISP chose such a policy they could do that. On this subject: When they say "do not add it to their routing table" do you know if they mean the BGP table or the IP table? i.e. if the ISP in question does a "sh ip bgp route <your prefix>" does it show in the list. Yet when they do a "sh ip route <your prefix>" it does not. If so then your ISP will be preferring a different route. Are you certain that the prefix filters this ISP is using - well sounds like they are using - are the same as the prefixes you are announcing? It could be that the prefix list is misconfigured. -- Cheers Dg
On Fri, 8 Apr 2005, Philip Lavine wrote:
I am prepending my AS 3 times to the un-preferred ISP. Both ISP's are my peers.
Ok...I just wanted to be sure you weren't prepending their ASN in which case loop detection would stop them from accepting your routes.
The un-preferred ISP claims the see my advertisement yet they do not add it to their routing table (suggests filtering??). They claim all the
Does the un-preferred ISP actually have no route back to you, or just not the one you sent to them? Depending on how things are setup, they may prefer your preferred ISP for reaching you. If you want "un-preferred ISP" to reach you directly, but still be "un-preferred", you may want to see if they have communities you can tag your advertisement with that would cause them to prepend your routes when propogating them to their peers. ---------------------------------------------------------------------- Jon Lewis | I route Senior Network Engineer | therefore you are Atlantic Net | _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
Philip Lavine wrote:
Update:
I am prepending my AS 3 times to the un-preferred ISP. Both ISP's are my peers. The un-preferred ISP claims the see my advertisement yet they do not add it to their routing table (suggests filtering??). They claim all the filtering they are doing is based on the networks I told them over the phone that I was using with that AS.
I have heard of providers who filter on AS path, and filter in such a way that more than N prepends (for varying values of N) causes the route(s) to be rejected. This could potentially be your problem. If they do soft-reconfig in on their customer sessions, they may see the route but filter it out. pt
participants (4)
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David Gethings -
Jon Lewis -
Pete Templin -
Philip Lavine