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New Member

eBGP iBGP and miltiple ISPs

I have a strange setup (inherited but not created by me) 3 ISPs, BGP with all of them. I take full routes from ISP 1 (mid sized) partial routes from ISP 2 (Huge) and am trying to add ISP3 at another location. The locations are connected via 2 T1s Both locations have cisco 7206vxr NPE 300s. I have ibgp set up between the 2 locations, it's talking but does not seem to redistribute the routes. I see them when I do a sh ip bgp, but I can't use them (it times out) Another problem is that for some reason I have no advertised routes. Granted my BGP is very rusty, and was never great.

gw2>sh ip bgp neighbors 207.x.x.x advertised-routes

gw2>

my config may be wong I dunno (on the router that doesn't announce anything):

router bgp xxxx

bgp log-neighbor-changes

network x.x.x.x mask 255.255.224.0

network x.x.y.x mask 255.255.224.0

neighbor a.b.c.d remote-as xxxx

neighbor a.b.c.d next-hop-self

neighbor w.x.y.z remote-as xxxy

neighbor w.x.y.z ebgp-multihop 2

no auto-summary

I can provide any other information if needed.

4 REPLIES
New Member

Re: eBGP iBGP and miltiple ISPs

There are several issues that will keep routes in the BGP table out of the routing table.

The first thing I notice is that the

"no synchronization" command isn't present.

It is required if you do not want to redistribute BGP into your IGP (generally a bad idea to redistribute).

The second major cause is that BGP will, by default, advertise the next hop as the router in the next AS.

If that route (BGP next hop) is not in the routing table, the BGP routes will not be inserted in the table. The fix for this is the next-hop-self. It appears that this is correct in your config, but without addresses, it’s hard to be absolutely sure.

HTH

Doug

New Member

Re: eBGP iBGP and miltiple ISPs

Problem 1: Can you elaborate on your first question?

Problem 2: You need to have two things accomplished in order for BGP to advertise.

a) have a network statement - which you do.

b) you need to have that exact block in the router's routing table. ex: if you have network x.x.x.x mask 255.255.224.0, when you do sh ip route x.x.x.x 255.255.224.0, x.x.x.x/19 has to be pointing somewhere rather it be null0 or a router it doesn't care.

New Member

Re: eBGP iBGP and miltiple ISPs

Deffinitelly the no synchronization will help.

Second, check the BGP conf on all the neighbors that concern you. What may be happening is that you are redistributing but they "dont want to learn from you" or they are not redistributing to your AS.

Look for ip as-path statements and access-list that is in the other bgp statements, for example:

neighbor x.x.x.x distribute-list XXX out or

neighbor x.x.x.x filter-list XXX in

Hope this helps, but to be more specific I'll have to see all the bgp confs on all the routers (if possible) and the sh ip bgp output

Velimir

New Member

Re: eBGP iBGP and miltiple ISPs

Thanks everyone, it was the "no synchronization" command. I just sat down with my trusty old "Internet Routing Architectures" book and read till I figured it out. right about then I checked back here and I found that you all had already given me an answer. t's good to see so much help is readily available, again, thanks.

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