Subject: RE: [Isis-wg] doubts

From: ramanathan rams <[email-masked]>
Date: Thu, 26 Sep 2002 15:53:07 -0700

hi,

       the diagram which I referred in my mail was ur first diagram not 
this. B and D are connected in PP circuit. A and B are in LAN.
further  PSNP interval is 2 secs. So after processing the CSNP, PSNP may 
not be immediately sent. so by that time if minimum LSP generation interval 
is expired then there is a chance that it can happen.

      but any way one extra send might result  and it could be either new 
or old. is this right or wrong?

thanks
rams.

-----Original Message-----
From:	Jeff Parker [SMTP:[email-masked]]
Sent:	Thursday, September 26, 2002 3:29 PM
To:	[email-masked]'; Jeff Parker
Cc:	[email-masked]'
Subject:	RE: [Isis-wg] doubts

>      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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