From: Dan C (cdan2154@gmail.com)
Date: Wed Mar 21 2007 - 01:23:38 ART
Hi Antonio,
Thank you for the contribution. Please consider this scenario:
You only have access to R1, you run all the debugs and know that the correct
AS no for R2 is 200 then you go ahead and change in R1 remote-as to 200.
On R2 you still have the wrong remote-as no.....
Now without having access to R2 can you configure in any way R1 to get the
wrong configured remote-as from R1 ?
Cheers,
Dan
On 3/21/07, Antonio Soares <amsoares@netcabo.pt> wrote:
>
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Yes, see this example:
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> R1(config)#router bgp 100
> R1(config-router)#
> R1(config-router)#neighbor 183.1.28.2 remote 300
> AS100(config-router)#
> 3d02h: %BGP-3-NOTIFICATION: received from neighbor 183.1.28.2 2/2 (peer in
> wrong AS) 2 bytes 0064
> R1(config-router)#
> 3d03h: %BGP-3-NOTIFICATION: received from neighbor 183.1.28.2 2/2 (peer in
> wrong AS) 2 bytes 0064
> R1(config-router)#
>
> R2(config)#router bgp 200
> R2(config-router)#neighbor 183.1.28.8 remote 400
> .Mar 28 08:33:09.251: %BGP-3-NOTIFICATION: sent to neighbor 183.1.28.8 2/2
> (peer in wrong AS) 2 bytes 0064
> R2(config-router)# FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 002D 0104 0064
> 00B4 9601 0808 1002 0601 0400 0100 0102 0280 0002 0202 00
> R2(config-router)#
> .Mar 28 08:33:48.163: %BGP-3-NOTIFICATION: sent to neighbor 183.1.28.8 2/2
> (peer in wrong AS) 2 bytes 0064
> R2(config-router)# FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 002D 0104 0064
> 00B4 9601 0808 1002 0601 0400 0100 0102 0280 0002 0202 00
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Router R2 informs R1 that R1 is in the wrong AS (0x0064=100). Now we know
> that R1 is in AS100 so let's correct this:
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> R2(config-router)#no neighbor 183.1.28.8 remote 400
> R2(config-router)#
> R2(config-router)# neighbor 183.1.28.8 remote 100
> R2(config-router)#
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Now R1 says that R2 is in the wrong AS (0x00C8=200):
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 3d03h: %BGP-3-NOTIFICATION: sent to neighbor 183.1.28.2 2/2 (peer in wrong
> AS) 2 bytes 00C8
> R1(config-router)# FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 002D 0104 00C8
> 00B4 9601 0202 1002 0601 0400 0100 0102 0280 0002 0202 00
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> So let's correct in R1:
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> R1(config-router)#no neighbor 183.1.28.2 remote 300
> R1(config-router)# neighbor 183.1.28.2 remote 200
> R1(config-router)#
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> And we have it:
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> R1(config-router)#
> 3d03h: %BGP-5-ADJCHANGE: neighbor 183.1.28.2 Up
> R1(config-router)#
>
> Rack1R2(config-router)#
> .Mar 28 08:42:29.011: %BGP-5-ADJCHANGE: neighbor 183.1.28.8 Up
> Rack1R2(config-router)#
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
>
>
> -----Original Message-----
> From: Cecil Wilson [mailto:Cecil.Wilson@flextronics.com]
> Sent: terga-feira, 20 de Margo de 2007 19:23
> To: Antonio Soares; iyux2000@gmail.com; ccielab@groupstudy.com
> Subject: RE: Debug BGP Question
>
> Hello
>
> are you saying this is one way to find the remote AS?
>
> (peer in wrong AS) 2 bytes 0036 hex for AS54?
>
>
>
>
>
>
>
> Cecil G. Wilson
>
> IT Network Services
>
> Office: (901) 215-2710
>
> Cell: (901) 601-6201
>
> cecil.wilson@flectronics.com
>
>
>
>
>
> -----Original Message-----
>
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>
> Antonio Soares
>
> Sent: Tuesday, March 20, 2007 8:43 AM
>
> To: iyux2000@gmail.com; ccielab@groupstudy.com
>
> Subject: RE: Debug BGP Question
>
>
>
> Whenever you have a misconfiguration, your local router will send a BGP
>
> notification to the other peer like this:
>
>
>
> %BGP-3-NOTIFICATION: sent to neighbor 54.1.1.254 2/2 (peer in wrong AS)
>
> 2 bytes 0036 FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 002D 0104 0036 00B4
>
> D412
>
> 0301 1002 0601 0400 0100 0102 0280 0002 0202 00
>
>
>
> Here 0x0036 means BGP AS54. So the local router is saying to its peer
>
> that it's in the wrong AS=54. This way is know the remote AS.
>
>
>
> -----Original Message-----
>
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>
> iyux2000@gmail.com
>
> Sent: segunda-feira, 19 de Margo de 2007 23:17
>
> To: ccielab@groupstudy.com
>
> Subject: Debug BGP Question
>
>
>
> Good morning, GS
>
>
>
> I have a question regarding to the real lab exam, i'am sure that it
>
> awlays ask you configure "local-as" command due to the neighbor
>
> configured with the wrong as. But if the question didn't tell you the
>
> wrong AS number that is configured on the other side (e.g. on BB1). Is
>
> there possible a way to find the wrong-AS-number from the BGP debug
>
> command? I tried serveral debug commands, but i can not figure it out.
>
>
>
> Thank you for your reply.
>
>
>
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