Subject: [Isis-wg] AreaMisMatch Event

From: "Chan, Chung Ming" <[email-masked]>
Date: Fri, 9 Nov 2001 05:59:22 -1000

Hi,
	I've a question regarding to Area Address mismatch. Hope someone can
clarify that to me.

	According to ISO/IEC 10589, section 8.4.2.2, item a)
	
"If a match is not found between any pair (i.e. the local
and remote system have no area address in common), the
IS shall reject the adjacency"

My understanding of the phase  "reject the adjacency" means:
1) If the IS  is not already have an adjacency with the remote IS, then
don't form any adjacency using the received IIH (Essentially drops/discards
the IIH)
2) If the IS  is already have an adjacency with the remote IS, then the IS
shall "reset the adjacency with the remote IS." (i.e. the IS goes back to
Enabled state, sending IIH without the MAC address of the remote IS).  My
reasoning is that  if the remote IS's area address is changed and there is
not area address in common any more, there is no more reason for keeping the
adjacency.

I know #1 shall be TRUE; but not sure about #2.

Could anyone help to clarify that?

Thanks,

Ming Chan

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From: Henk Smit <[email-masked]>
Date: Fri, 9 Nov 2001 15:29:34 -0800 (PST)

Seems like I am the only one to disagree with the rest. :-)

  I would prefer my code to just ignore the incoming IIH and drop it.
 If the other router was really reconfigured with different area address(es)
 then the next few IIHs will be dropped too, causing the adjacency to time
 out eventually.

  This will take some time. And could be speed up by bringing down the
 adjacency immediately. What do you gain ? If a network admin really
 wants the adjacency to be reset quickly, he can clear it manually after
 the manual area address change.

  The downside of clearing the adjacency is that you are making your
 network less robust.
  Remember that IIHs have no layer3 checksum. So in case you are
 receiving a (partially) corrupted packet, this one corrupted packet
 can take down an adjacency immediately. If you just ignore the packet,
 and it was really an incidental corruption, the adjacency stays up.
  In a previous life I've seen this happen on ATM networks.

        Henk.

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From: mike shand <[email-masked]>
Date: Mon, 12 Nov 2001 08:48:47 +0000

>   Seems like I am the only one to disagree with the rest. :-)

Good point Henk, I agree (although I suspect this wasn't what we meant when 
we wrote 10589).

         Mike