Subject: RE: [Isis-wg] doubts

From: Jeff Parker <[email-masked]>
Date: Thu, 26 Sep 2002 18:29:05 -0400

>      old LSP will be sent when SRM flag is examined before 
> getting the new 
> LSP update from the DIS.     B receives the CSNP packet from 
> A, finds it is 
> having a old copy so it will set the SSN bit, to request the 
> new version of 
> that LSP. Meanwhile another   new version of the LSP comes 
> from D which is 
> not as latest as A is having. but to B, it is latest and it 
> will update the 
> database and set the SRM flag,  then SSN request is sent and 
> then because 
> of SRM flag set, B will send the LSP received from D on the 
> LAN before 
> receiving the new ( latest ) LSP from  DIS.  In this case old LSP is 
> propogated.
> 
>       new lsp will be sent when SRM flag is examined after 
> getting the new 
> update from the DIS.
> 
>  is that right or wrong?
> 
> thanks
> rams.

Rams -

Three routers, with three version of LSP X

	X3   X1    X2

	A*    B    D
	|     |    |
    =================

A is DIS, sends CSNP.  
B sees it, marks SSN bit to request it.
D then sends X2, which B replaces.
Is this your scenario?

Note that D's transmission is a race condition
with A's CSNP.  If D had processed the CSNP, he
would send a PSNP rather than an LSP.  Further,
if A is including the LSP in the CSNP, it probably
send LSP X3 out recently, so neither B nor D
should have the wrong stuff.  

This is a distributed database: there is going
to be extra packets.  However, it does converge,
and it converges pretty quickly.  The scenario
you describe is -possible-, but doesn't look
likely.

- jeff parker
- axiowave networks
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