BGP Peers

Unanswered Question
May 20th, 2007
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When i doing the BGP home lab, i came to notice that when iam establishing the BGP session between the two private AS which comes under a single public AS

It is forming the adjacency without giving the command #bgp confederation peers (Private AS number)

The one of the router is running of Version 12.2(5)and other router router is 12.2(8)

I dont know why its happening and i tried of shutdown the interface and made the interface UP, same think is happening

can u help me know abt the issue,other think when i try to establish the bgp session between the One public AS to other Privte AS (Which comes under a Public As)without giving the command # bgp conferderation identifier (Public AS)

Then it showing me the NOTIFICATION ERROR MSG

So Why not the above think is not happening

Thanks in advance


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bjornarsb Mon, 05/21/2007 - 00:18
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I belive that you have to specify both

confederation identifier and every peer you have in you condederation to make this work:

router bgp 2120

bgp confederation identifier 500

bgp confederation peers 6001 6003

neighbor remote-as 6002

neighbor remote-as 6001

neighbor remote-as 6003

neighbor remote-as 700



vinoth.kumar Mon, 05/21/2007 - 01:45
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Thanks for information,

As 65510 R1----------R2 AS 65520

---------------------------------------------Both R1 and R2 comes under Public AS of 20

What i want to know is whether the TCP connection will establish without giving the command as

R1 # BGP Conferderation peer 65520

and in

R2 # BGP Conferderation peers 65510



CSCO10892433 Mon, 05/21/2007 - 03:32
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Hi, vinoth

Without the bgp confederation peer command, both routers will see each other as a true EBGP peer. R1 will send an open message with AS=20 to R2 and expect to recevie an open message from R2 with AS=65520.

R2 do the same thing.(send an open message with AS=20 and expect to receive an open message with AS=65510). And the result is a wrong-AS issue. Theorectically, the BGP session cannot be established.

And why did your routers can establsh the session successfully? I don't know. Wait the expert to answer you.(Harold, where are you?) Before that, it's a good idea to issue the debug ip bgp command on your routers and see what messages are brought to you.



Harold Ritter Mon, 05/21/2007 - 05:14
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You are correct the session should not come up given the above scenario.


Can you provide the full configurations from both R1 and R2 that led to that mysterious behavior.


vinoth.kumar Mon, 05/21/2007 - 21:44
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R2 ----------------- R3

As|65510 As 65520


| Public As 20




Public As 10

R1#Router bgp 10

#neighbour remote-as 65510


R2#router bgp 65510

#neighbour remote-as 65520

#neighbour remote-as 10

#bgp conferderation identifier 10

R3#router bgp 65520

#neighbour remote-as 65510

This what i have done in my home lab and i found that the adjacency is formed between the routers

can u suggest me were is the route cause for this issue

Note : R2 is running on version 12.2 (5)

R3 is running on version 12.2 (8)

Thanks in advance,


CSCO10892433 Tue, 05/22/2007 - 03:27
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Hi, Vinoth

I try your config and the result is the same.

R2's debugging message

received from neighbor 2/2 (peer in wrong AS) 2 bytes 0014

R3's debugging message

BGP: bad OPEN, remote AS is 20, expected 65510

show ip bgp summary on R2

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 4 65520 8 8 0 0 0 never Active

show ip bgp summary on R3

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 4 65510 8 8 0 0 0 never Active

Would you please post your output of "debug ip bgp" and "show ip bgp summary"?


Harold Ritter Tue, 05/22/2007 - 04:50
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This is not normal. I tried with 12.2(10) and the session didn't come up.

You are probably running in to some older bug. I would suggest you try with more recent code, in which case you should see that the session won't form.

Hope this helps,


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