BGP question

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May 20th, 2009
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All,


I have a remote site that was converted to a different type of connection, but we're peering with the same ISP.


The following settings (summarized) are on the interface of the remote router:


Serial0: 172.30.9.1


BGP:

network 10.5.5.0 mask 255.255.255.0

network 172.21.9.0 mask 255.255.255.0

neighbor 172.30.9.2 remote-as xxxx


I can ping 10.5.5.x, and I can ping 172.30.9.1. The network statement for 172.30.9.0 isn't in the BGP process, so I *assume* that it's because I'm peering on that same network is why I can see it? The ISP would be peering with 172.30.9.1, so I'm assuming that's why I can see it.


Thanks,

John



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Jon Marshall Wed, 05/20/2009 - 06:55
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John


Do you have a "redistribute connected" under your BGP config ?


If you do "sh ip bgp neigh 172.30.9.2 advertised-routes" do you see the 172.30.9.1 network ?


Jon

John Blakley Wed, 05/20/2009 - 07:02
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Jon,


I do see a listing for it, and we're only redistributing static routes.


Thanks!

John

Jon Marshall Wed, 05/20/2009 - 07:07
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John


When you say a listing do you mean it appears in the output of "sh ip bgp neigh ....advertised-routes" ?


Do you have a static route for it on the router ?


Jon

John Blakley Wed, 05/20/2009 - 07:12
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No static routes anywhere. Here's what I get from my local router. (The router in question is on the other side of the provider.)


*> 172.30.5.0/30 172.16.10.2 0 13979 ?

*> 172.30.9.0/30 172.16.10.2 0 13979 ?



172.16.10.2 is my local router that all of my remote sites terminate to.


I have two that I've found that I missed putting the network under their BGP process. I'm going to add it, after hours, but it's still in the table. I was under the impression that if you wanted a network to show up, you needed to put the network under the process. I can only figure that the provider is doing something on their end.


Thanks,

John

Jon Marshall Wed, 05/20/2009 - 07:15
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John


"I was under the impression that if you wanted a network to show up, you needed to put the network under the process."


Yes that's my understanding as well unless of course you are redistributing your IGP into BGP.


Jon

John Blakley Wed, 05/20/2009 - 07:29
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Jon,


I'm not running any IGP at all. It's redistributing statics, but there aren't any statics defined on that router. Can there be any other reason why I would see a route to something that's not being advertised through BGP? Would it make sense that the provider could be doing something where I have a /30 network with them, and since there can only be two hosts, that's why it's seeing it? I have to routers here that I could test with, but I'd need to get an image that supported BGP. That's the only thing that I can think of.


John

jason.chilton Wed, 05/20/2009 - 07:42
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The provider is advertising the address space into BGP. The AS path is only 13979 (ATT) so they are originating it.

pauloroque Wed, 05/20/2009 - 07:18
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Hi John,


Whais the state of the bgp connection? 'sh ip bgp summary'.


Is the synchronization on the remote router turned off?

--

bgp xxx

no synchronization

--

Is the prefix 172.30.9.0/24 on the remote router routing table? If not, make sure create a static 'ip route 172.30.9.0/24 null0' or inject this prefix dynamicly.


Paulo Roque



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