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BGP Multi-Homed but traffic likes Sprint better =(

Hi, I have two Cisco routes that are running BGP between Level3 and Sprint. The BGP configs on both are pretty much the same and look something like this:

router bgp 12345 no synchronization bgp log-neighbor-changes neighbor 192.168.1.1 remote-as 26383 neighbor 192.168.1.1 description iBGP link to hydra neighbor 192.168.1.1 password 7 password neighbor 192.168.1.1 version 4 neighbor 192.168.1.1 soft-reconfiguration inbound neighbor 160.81.248.77 remote-as 1239 neighbor 160.81.248.77 description ebgp link to sprint neighbor 160.81.248.77 version 4 neighbor 160.81.248.77 soft-reconfiguration inbound no auto-summary

The other router is configured similarly. HOWEVER, if I do a show ip bgp 209.245.19.41 (level3.net) I get: BGP routing table entry for 209.244.0.0/14, version 891496 Paths: (2 available, best #1, table Default-IP-Routing-Table) Not advertised to any peer 1239 3356, (aggregated by 3356 4.69.130.12), (received & used) 160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78) Origin IGP, metric 34, localpref 100, valid, internal, atomic- aggregate, best 32327 7911 3356, (aggregated by 3356 4.69.130.10), (received & used) 209.183.177.125 from 209.183.177.125 (209.183.191.194) Origin IGP, localpref 100, valid, external, atomic-aggregate

Why is Level3 prefering to go out Sprint (160.81.248.77) rather then go out Level3 (209.183.177.125)? I see there seems to be an extra AS hop there, but why? Shouldn't a L3 pipe be a better route to L3?

Reply to
mhoppes
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AH! Answered my own question. My L3 pipe is going through another carrier (I knew that), who is putting another AS number in there... so my question, then, is.. what do I need to do to get the routes to look even? Appending another AS number will, I believe, only affect inbound traffic.

Reply to
mhoppes

route map addmyas permit 10 set as-prepend ! router bgp neighbour sprint route-map addmyas in neighbour sprint route-map addmyas out

Reply to
Lutz Donnerhacke

Ok.. that worked as expected: Hydra#show ip bgp 206.80.67.28 BGP routing table entry for 206.80.64.0/21, version 402504 Paths: (2 available, best #1, table Default-IP-Routing-Table) Flag: 0x208 Not advertised to any peer 26383 1239 3356 30512, (received & used) 160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78) Origin IGP, metric 34, localpref 100, valid, internal, best 32327 7911 3356 30512, (received-only) 209.183.177.125 from 209.183.177.125 (209.183.191.194) Origin IGP, localpref 100, valid, external

However, why is Sprint still being preferred? I don't want to send ALL traffic down L3.. just traffic that is, well you know, going to the L3 network! Even level3.net (the last entry there at 4.68.95.11) has fewer AS hops going over L3, yet it still wants to go out Sprint!

The other odd thing is if I do a show command for L3 (4.68.95.11) on my L3 router I get: Hydra#show ip bgp 4.68.95.11 BGP routing table entry for 4.0.0.0/9, version 225677 Paths: (2 available, best #2, table Default-IP-Routing-Table) Not advertised to any peer 32327 7911 3356, (aggregated by 3356 4.69.130.10), (received-only) 209.183.177.125 from 209.183.177.125 (209.183.191.194) Origin IGP, localpref 100, valid, external, atomic-aggregate 26383 1239 3356, (aggregated by 3356 4.69.130.12), (received & used) 160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78) Origin IGP, metric 34, localpref 100, valid, internal, atomic- aggregate, best Hey it's working! But if I do it on my Sprint router I get:

medusa#show ip bgp 4.68.95.11 BGP routing table entry for 4.0.0.0/9, version 923707 Paths: (2 available, best #1, table Default-IP-Routing-Table) Advertised to non peer-group peers: 65.165.94.77 65.173.16.33 26383 1239 3356, (aggregated by 3356 4.69.130.12) 160.81.248.77 from 160.81.248.77 (144.228.242.72) Origin IGP, metric 34, localpref 100, valid, external, atomic- aggregate, best 1239 3356, (aggregated by 3356 4.69.130.12), (received-only) 160.81.248.77 from 160.81.248.77 (144.228.242.72) Origin IGP, metric 34, localpref 100, valid, external, atomic- aggregate eh?

Reply to
mhoppes

It's called hot potato routing. Every router prefers it's own peers if all other paramters are equal. In order to load balance your outgoing traffic, you have to load balance the traffic in your own network to the routers.

OTOH from two routes with equal length, weight and preference the oldest onw is prefered (assuming this one is more stable).

Reply to
Lutz Donnerhacke

Ok.. I understand this.. and indeed things now look like they should on the L3 router.. so my question would then be... what would I need to do on the Sprint router to get it to ship traffic over to the L3 router? Ideally our L3 traffic would go there (a few subnets), but best case would be I could get about half our traffic going out there, and leave half on Sprint.

Reply to
mhoppes

Match the L3 prefixes coming in via the L3 connection and then set a higher local pref to be used within your network to prefer the L3 connection over the Sprint connection.

Chris.

Reply to
Chris

Can you, or someone else, provide an example? Although I'm fairly fluent in CISO-ios, my BGP knowledge is rather rusty.

Reply to
mhoppes

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