From: Huan Pham (Huan.Pham@peopletelecom.com.au)
Date: Thu Aug 07 2008 - 23:03:06 ART
Hi Asheesh,
I saw this question asked before in the GS, but I have not seen an
answer for your need yet.
http://www.groupstudy.com/archives/ccielab/200511/msg00250.html
I believe that the short answer is on your router (with show/debug) you
won't be able to see what "remote-as" is configured for your router on
the neighbor router. You need some sort of access to it (e.g. Telnet,
SNMP, or even Netflow e.g. ip flow-export {version}[peer-as |
origin-as]) to get the info.
I believe this is because the peer-as information is not standardized in
any messages exchanged between the peers the RFC.
According to RFC1771 for BGP-v4, there're 4 types of message for BGP:
OPEN, UPDATE, NOTIFICATION and KEEPALIVE. As the BGP neighbor
relationship has not been established, we are only concerned with OPEN,
and NOTIFICATION. According to RFC, the messages exchanged only include
what AS number configured, and not What AS a router expect from remote
peer. In other words, as a BGP router, I will tell you my AS, which also
means the remote-as for my router you should configure on Your router.
If you configured it wrongly, I will return "Wrong AS" error code. The
router does not metion what AS number it expects from peer (the number
your configured with neighbor remote-as command).
To extend the functionality specified in RFC, Cisco can add this info in
the NOTIFICATION message (data field) to make the debugging easier, but
as far as I can tell, I do not see the IOS works that way at the moment.
Cheers,
Huan
http://www.ietf.org/rfc/rfc1771.txt
1 - OPEN
2 - UPDATE
3 - NOTIFICATION
4 - KEEPALIVE
the OPEN message contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Autonomous System |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hold Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BGP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opt Parm Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Parameters |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.5 NOTIFICATION Message Format
A NOTIFICATION message is sent when an error condition is detected.
The BGP connection is closed immediately after sending it.
In addition to the fixed-size BGP header, the NOTIFICATION message
contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error code | Error subcode | Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OPEN Message Error subcodes:
1 - Unsupported Version Number.
2 - Bad Peer AS.
3 - Bad BGP Identifier. '
6.2 OPEN message error handling.
If the Autonomous System field of the OPEN message is unacceptable,
then the Error Subcode is set to Bad Peer AS. The determination of
acceptable Autonomous System numbers is outside the scope of this
protocol.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
asheesh mamgain
Sent: Friday, 8 August 2008 5:34 AM
To: Cisco certification
Subject: bgp local as
Hi experts,
just wonndering how to see the as information if the other router has
configured it wrongly. Tried different bgp debug but couldnt get it.
regards
ashish
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