nanog mailing list archives
Re: AS prepending
From: Philip Lavine <source_route () yahoo com>
Date: Fri, 8 Apr 2005 09:05:59 -0700 (PDT)
Update 2: More info. When I have tested the failover by pulling the plug on the preferred ISP, I do not see my network in looking glass. Secondly, the backup provider has told me the the route is not in the (rib). Philip --- Mark Kasten <mark.kasten () savvis net> wrote:
<offlist> fwiw, it's in the routing table (rib), not their forwarding table (fib). if they look on their side of the session, they will have the prefix in "show ip bgp" or "show route", but it will not propogate beyond that router because their network prefers the other path with the short AS. a router doesn't forward all rib entries, only fib entries. for example: dcr4.nyr> show route 141.77.0.0/16 141.77.0.0/16 *[BGP/170] 3w4d 01:53:30, MED 98, localpref 100, from 206.24.194.105 AS path: 1273 ? > via so-0/0/0.1510 via so-1/1/0.10 [BGP/170] 9w3d 12:26:09, MED 128, localpref 80 AS path: 3356 1273 I > to 4.68.127.205 via so-6/1/0.0 [BGP/170] 21:32:50, MED 128, localpref 80 AS path: 1239 1273 ? > to 144.232.9.117 via so-3/1/0.0 on a router, one hop away: kar1.nyr> show route 141.77.0.0/16 inet.0: 173067 destinations, 345433 routes (172951 active, 0 holddown, 547 hidden) Restart Complete + = Active Route, - = Last Active, * = Both 141.77.0.0/16 *[BGP/170] 3w4d 01:53:59, MED 98, localpref 100, from 206.24.194.105 AS path: 1273 ? > to 208.174.228.1 via ae0.0 no evidence of the 3356_1273 or the 1239_1273 path. if i lose the direct 1273 path, then one of those paths would then be propogated as the preferred path. hth's. mark Philip Lavine wrote:Update: I am prepending my AS 3 times to the un-preferredISP.Both ISP's are my peers. The un-preferred ISPclaimsthe see my advertisement yet they do not add it to their routing table (suggests filtering??). Theyclaimall the filtering they are doing is based on the networks I told them over the phone that I wasusingwith 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.Whydoes the ISP receiving the prepends fail to addmynetwork 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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Current thread:
- AS prepending Philip Lavine (Apr 08)
- Re: AS prepending Patrick W Gilmore (Apr 08)
- Re: AS prepending Hank Nussbacher (Apr 09)
- Re: AS prepending Jon Lewis (Apr 08)
- <Possible follow-ups>
- Re: AS prepending christian . macnevin (Apr 08)
- Re: AS prepending Philip Lavine (Apr 08)
- Re: AS prepending David Gethings (Apr 08)
- Re: AS prepending Jon Lewis (Apr 08)
- Re: AS prepending Pete Templin (Apr 08)
- Re: AS prepending Philip Lavine (Apr 08)
- Re: AS prepending David Gethings (Apr 08)
- Re: AS prepending David Barak (Apr 08)
- Re: AS prepending Patrick W Gilmore (Apr 08)