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  From: John Edwards <isplist@adam.com.au>
  To  : Glen Turner <glen.turner@aarnet.edu.au>
  Date: Mon, 14 Jul 2003 14:49:10 +0930

Re: Anyone going to meeting with laptop with GbE?

Glen Turner wrote:

> A lot of switch and router vendors support "jumbo frames",
> these are 9000 bytes.  With that installed base, an
> alternative approach is for ISPs to decide that 9000
> will be the new gigabit MTU and deploy it where possible.
> The ISP having a bigger MTU on their backbone doesn't hurt
> existing normal-MTU ethernet users.


There is increasing demand for tunnelled services (L2TP, PPP, MPLS, 
QinQ) with a full 1500 MTU available, which is of course impossible on 
standard ethernet. If 9000 MTU becomes the new standard, are we going to 
end up with the same "Russian Doll" problem with encapsulation/tagging, 
or are you hoping to fix PMTU once and for all at the same time so that 
9000MTU inside tunnels is never a requirement? A 'soft limit' on MTU 
would be nice, but I guess it would break too many other things.

Is there any way that 9000 MTU and 1500 MTU devices will be able to 
co-exist on the same ethernet segment and talk to each other, or will 
this remain the task of a router?

John Edwards


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