From: Han Ghee Chia (han_ghee@yahoo.com.sg)
Date: Tue Jun 28 2005 - 23:46:02 GMT-3
No. The remote router will report that your AS is wrong but it will NOT tell you what it was expecting.
That's from what I see from the debug messages and what I understand about the OPEN and NOTIFICATION messages of BGP.
Kindly correct me if you think I'm wrong.
Thanks
Han Ghee
Lee Donald <Lee.Donald@t-systems.co.uk> wrote:
Not sure I understand that Han.
Debug ip bgp will give me the messages from the remote router reporting my
AS is wrong and telling me what it was expecting.
Yes ?
Regards
Lee.
-----Original Message-----
From: Han Ghee Chia [mailto:han_ghee@yahoo.com.sg]
Sent: 28 June 2005 01:54
To: ccielab@groupstudy.com
Subject: RE: BGP Wrong AS
Hi Lee,
"debug ip bgp" will provide one with the AS that is being expected by the
LOCAL router, versus what it actually see in the OPEN message from its peer.
"debug ip bgp" will show the REMOTE router's AS number if the LOCAL router
got its peer remote-as number wrong.
If the REMOTE router is configured with a wrong remote-as number for its
peer, it will NOT be shown in the LOCAL router's "debug ip bgp" messages.
I think, the above is different from what you wrote that "the debug ip bgp
will provide you with the AS that is being expected by your peer". Hope I
didn't got your meaning wrong.
Regards
Han Ghee
Lee Donald wrote:
Yes, the debug ip bgp will provide you with the AS that is being expected by
your peer. There is no conversion to do.
I don't know which would be reported first, the password or the wrong AS but
they are both reported in the debug. Once you got one, you'd have to get the
other.
Regards
Lee.
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: 27 June 2005 12:24
To: 'Lee Donald'; 'Han Ghee Chia'; ccielab@groupstudy.com
Subject: RE: BGP Wrong AS
Hey guys,
Since we're talking about this anyway, let's take it to the extreme.
Suppose, in the lab, you had to ebgp peer your router to the backbone router
but you're not told what AS the backbone router is in.
Could debug ip bgp be used to figure out the AS of the backbone?
If so, what would we look for in the debug output and would we have to
translate from hex?
Also, suppose we could use the debug output to determine the AS of the
remote peer, if the peering were protected by a password, would we still be
able to determine what the remote AS was?
Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Lee
Donald
Sent: Monday, June 27, 2005 6:07 AM
To: Han Ghee Chia; ccielab@groupstudy.com
Subject: RE: BGP Wrong AS
That's weird.
I'm going to try it a couple of ways round.
Thanks.
Lee.
-----Original Message-----
From: Han Ghee Chia [mailto:han_ghee@yahoo.com.sg]
Sent: 27 June 2005 10:52
To: ccielab@groupstudy.com
Subject: RE: BGP Wrong AS
Hi Lee,
May I know if you are referring to a debug output as follows: -
" BGP: 2.2.2.2 bad OPEN, remote AS is 3, expected 2"
I just did a simple test, and I got the above output using "debug ip bgp",
however there is a difference between what both routers see: -
For e.g.
R1 is in AS 1, thinks that R2 is in AS 2
R2 is in AS 3, thinks that R1 is in AS 1 (which is correct)
R1 with see this message,
" BGP: 2.2.2.2 bad OPEN, remote AS is 3, expected 2"
But R2, will only see these 2 messages,
BGP: 1.1.1.1 rcv message type 3, length (excl. header) 4
%BGP-3-NOTIFICATION: received from neighbor 1.1.1.1 2/2 (peer in wrong AS) 2
bytes 0003
From my understanding on the BGP connection process, a NOTIFICATION message
will be sent whenever there is an error. In this case, R2 receives the
NOTIFICATION message from R1 about it being in the wrong AS. And the
message length is 4 bytes - 1 byte for error, 1 byte for error subcode, 2
byte for the AS number that is wrong.
Therefore, I think the only way to find out the correct AS number from your
end, is to ask the remote administrator.
Anyone has a better way ? Please kindly enlighten us. :-)
Regards
Han Ghee
Lee Donald wrote:
Hi Kieren,
That's seems to be on by default. I'm logging to the console so I should see
it but not.
Any other ideas ?
-----Original Message-----
From: k carter [mailto:kieren.carter@postremo.co.uk]
Sent: 27 June 2005 10:43
To: 'Lee Donald'
Subject: RE: BGP Wrong AS
Hi Lee,
Have you tried enabling "bgp log-neighbor-changes" under the BGP routing
process (don't forget to consider where the logging information is being
sent too)?
Cheers
Kieren
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Lee Donald
Sent: Monday, June 27, 2005 10:19 AM
To: James Yeo; Lee Donald; ccielab@groupstudy.com
Subject: RE: BGP Wrong AS
James,
I'm afraid you are wrong. I've seen it done a few times on courses and
even
used it before, but just can't remember it.
It says something like " AS sent 100, expected AS 254" or something like
that.
Regards
Lee.
-----Original Message-----
From: James Yeo [mailto:James.Yeo@arivia.co.za]
Sent: 27 June 2005 10:11
To: Lee Donald
Subject: RE: BGP Wrong AS
Lee,
They "IBM" would need to tell you there AS. Must be registered and if
you are forming proper Neighborships then you would need this from there
IT department.
When establishing neighbors you cannot debug and pick up the AS unless
you sniff the port for TCP traffic. I may be wrong though as this is a
security feature.
Hope that helps
James
-----Original Message-----
From: Lee Donald [mailto:Lee.Donald@t-systems.co.uk]
Sent: Monday, June 27, 2005 11:12 AM
To: James Yeo; Lee Donald; ccielab@groupstudy.com
Subject: RE: BGP Wrong AS
James,
How would that tell me what AS is expected?
Regards
Lee.
-----Original Message-----
From: James Yeo [mailto:James.Yeo@arivia.co.za]
Sent: 27 June 2005 10:05
To: Lee Donald
Subject: RE: BGP Wrong AS
Check your neighbor statement or Local-AS statement.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Lee Donald
Sent: Monday, June 27, 2005 10:48 AM
To: ccielab@groupstudy.com
Subject: BGP Wrong AS
I have a BGP Neighbour which is reporting that Ibm in the wrong AS but
I
canbt seem to find the debug that tells me exactly what AS it thinks
Ibm
in.
Can anybody tell me?
Thanks.
Regards
Lee Donald.
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