Subject: (IPng 6540) Re: Host Fragmentation

From: [email-masked] (Peter R. Tattam)
Date: Mon, 28 Sep 1998 11:14:47 +1100

Hmm.  At the risk of getting involved in a holy war, my only comment in reply 
is..

1.  I fully appreciate that IPv6 allows fragmentation.  In fact my stck 
implements it (hopefully correctly).

2. I can can fully appreciate should routers need not concern themselves with 
fragmentation due to the cost of having to do so as I outlined in my previous 
message.  The cost for a router is *much* more than would be for a host.  
I would guess that issues like packet forwarding time would become critical, 
and also I suspect that quality routers would be using high grade memory which 
would impact critically in a cost sensitive market.  Keeping hardware 
resources to a minimum is important from engineering and manufacturing point 
of view.  Applying the rule that fragmentation should not occur across the 
network removes some significant problems for backbone routers.  In general, 
memory is required for other more important things like BGP tables etc. Now 
how would you like it if some fragment bombed all the critical paths in your 
network connection?  Having the don't fragment bit forces routers to do 
fragmentation which is not good in the design of a router.

3.  I don't personally care whether fragmentation is in or out.  All I am 
saying is that it comes at a cost.  For future expansion of the internet it is 
important to do a cost analysis to measure the cost of implementation and 
maintenance of that internetwork.

Peter

--
Peter R. Tattam - Managing Director          
Trumpet Software International Pty Ltd.
Phone: +61-3-6245-0220     Fax: +61-3-6245-0210
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