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-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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On Friday 08 April 2005 17:05, Philip Lavine wrote:
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). In that case your only course of action is to ask why the ISP is filtering your routes. I doubt anyone on this list we be able to divine why the ISP is filtering your routes.
-- Cheers Dg
--- Philip Lavine <source_route@yahoo.com> wrote:
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
Have you verified that you're advertising the routes to them? In Cisco-speak, does sh ip bgp nei x.x.x.x adv return what you're expecting? Also, assuming that your backup ISP is either directly connected to (or one transit hop away from) your primary ISP, 3 prepends is too many for what you want. Try 1 prepend first. David Barak Need Geek Rock? Try The Franchise: http://www.listentothefranchise.com __________________________________ Yahoo! Messenger Show us what our next emoticon should look like. Join the fun. http://www.advision.webevents.yahoo.com/emoticontest
participants (3)
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David Barak -
David Gethings -
Philip Lavine