Subject: [Isis-wg] authentication.

From: ramanathan rams <[email-masked]>
Date: Thu, 25 Apr 2002 11:54:10 -0700

Hi all,

       I have a doubt in ISIS. could u please explain me?

       In ISIS we have authentication TLV. There is no restriction on this 
TLV whether to come in the front or not. so it can come in any place in all 
pdus( hello/LSP).

       So a receiver of the PDU has to go thro' the entire packet to  reach 
to the authentication TLV and then check whether the authentication 
condition is satisfied or not. But it seems to me a big overhead,  we need 
to scan the complete packet or to the point where that TLV is available. is 
there any reason behind this(i.e having the authentication TLV at any 
position, usually at the end)?.

       Generally we have checksum computation, that involves going thro' 
the whole packet and finally that result will be put in the packet header, 
so that receiving end can easily get the value and check it. similarly why 
not we can have a restriction that the Authentication TLV shud appear 
before all the TLVs so that processing will be easier.

thanks
rams.

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From: Alex Zinin <[email-masked]>
Date: Thu, 25 Apr 2002 12:46:47 -0700

Ramanathan,

 I brought this up a while ago.
 If we were sure that _all_ implementations already do
 put the Auth TLV at the beginning or at the end, one
 could take advantage of this. However, there seems to
 be no confidence in this, so you still have to be ready
 for the case where the TLV can appear anywhere in the PDU,
 and hence you don't really gain anything.

-- 
Alex