Subject: [Isis-wg] Hello Storm?

From: "Kandula, Ramesh" <[email-masked]>
Date: Fri, 31 Mar 2006 23:51:51 -1000

Hi all

Can someone explain why the following scenario does not happen?

Suppose two IS-IS routers (RTR1 and RT2) on a P2P link restart ~at the same
time. 

1. The RTR1 comes up first and sends a hello with RR=1, RA=0, state=Init
(P2P 3-way)
2. Then RTR2 comes up and as soon as it comes up it sends a hello with RR=1,
RA=0, state=Init (RTR2 didn't see RTR1's hello)
3. When RTR1 sees RTR2's hello, it notices it doesn't have an adjacency in
the Up state with RTR2, so it processes the hello normally. This causes
RTR1's state to go to Up (Should RTR1 care whether it has received Restart
Ack?). It sends a hello with RR=1, RA=1, state=Up (though not immediately)
4. When RTR2 sees RTR1's hello, it does the same as step 3. But now it sends
a hello immediately with RR=1, RA=1, state=Up.
5. When RTR1 sees this, it does the same as step 4.

     RR=1, RA=0, state=Init
1.  ---------------------------------->
                                                       RR=1, RA=0,
state=Init
 
2.<-------------------------------- 

     RR=1, RA=1, state=Up
3.  --------------------------------->
                                                       RR=1, RA=1, state=Up
 
4.<---------------------------------

     RR=1, RA=1, state=Up
5. -----------------------------------> 
.

Do these two routers keep sending hello's like this until T1 timer is
cancelled (due to expiry or otherwise)?

It was mentioned in the earlier posts that routers restarting around the
same time is very unlikely. Assuming that it can happen what is prevening
the hello storm descirbed above?

Thanks
ramesh

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