Subject: RE: [Isis-wg] Overload Bit

From: "Jeelani Syed" <[email-masked]>
Date: Fri, 8 Oct 2004 11:21:46 -0400

First of all overload state is assumed to be a temporary state and it is
undesirable to purge
all LSPs beloging to a router from network and reflood them instead of
just sending a LSP 
with overload bit set/reset.

-jeelani.sm

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On
Behalf Of Abhishek Verma
Sent: Friday, October 08, 2004 10:39 AM
To: [email-masked]
Subject: [Isis-wg] Overload Bit

Hi,

A -- B -- C

[1] A, B and C are 3 L1/L2 ISIS routers. B has its overload bit set.
This as per what i have read "ensures that no other router uses this
local router for transit traffic".

Now, here goes my problem(s):

ISIS adjacencies are up between these 3 routers. A is aware of C's
loopback and C is aware of A's loopback IP address. That could be say,
because we have added loopback interfaces to our areas.

Now if I try to ping A from C, should my ping go? 

IMO it shouldnt. Only the traffic destined to B's directly connected
interfaces should be allowed. Also does this technically mean that
when A receives an LSP from B with this bit set, it should not install
it?

If that is the case then why would B advertise its LSP in the first
place? When it knows that A and C are not going to use that?

Thanks,
Abhishek

--
Class of 2004
Institute of Technology, BHU
Varanasi, India

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From: Henk Smit <[email-masked]>
Date: Sat, 9 Oct 2004 01:00:34 +0200 (CEST)

> First of all overload state is assumed to be a temporary state

  Says who ?
 If a router wants to set the overload bit for ever, it is allowed to
 do so. There are cases where a constant setting of the overload bit
 is useful.

> and it is undesirable to purge

  1) Purging an LSP or 2) setting the overload bit
 are two totally different things, and should not be compared with
 each other.

  Also, purging one LSP or setting the overload bit on one LSP 
 requires roughly the same amount of work to be done by all
 routers (both actions require one router to create a new LSP,
 flood it to all routers, all routers do some LSPDB housekeeping,
 all routers run an SPF computation).

  Hope this helps,

        Henk.