Thoughts on increasing MTUs on the internet

Fri Apr 13 14:52:30 UTC 2007

I don't think it matters that everything can use jumbograms or that every single device on the Internet supports them. Heck, I still know networks with kit that does not support VLSM!

What would be good is if when a jumbogram capable path on the Internet exists, jumbograms can be used.

This way it does not matter than some box somewhere does not support anything greater than a 1500 byte MTU, anything with such a box in the path will simply not support a jumbogram. How do you find out? Just send a jumbogram across the path and see what happens.. ;-)

--
Leigh Porter
UK Broadband

-----Original Message-----
From: owner-nanog at merit.edu on behalf of Valdis.Kletnieks at vt.edu
Sent: Fri 4/13/2007 3:36 PM
To: Saku Ytti
Cc: NANOG list
Subject: Re: Thoughts on increasing MTUs on the internet

On Fri, 13 Apr 2007 08:22:49 +0300, Saku Ytti said:
> 
> On (2007-04-12 20:00 -0700), Stephen Satchell wrote:
>  
> > From a practical side, the cost of developing, qualifying, and selling 
> > new chipsets to handle jumbo packets would jack up the cost of inside 
> > equipment.  What is the payback?  How much money do you save going to 
> > jumbo packets?
> 
> It's rather hard to find ethernet gear operators could imagine using in
> peering or core that do not support +9k MTU's.

Note that the number of routers in the "core" is probably vastly outweighted
by the number of border and edge routers.  There's a *lot* of old eBay routers
out there - and until you get a clean path all the way back to the source
system, you won't *see* any 9K packets.

What's the business case for upgrading an older edge router to support 9K
MTU, when the only source of packets coming in is a network of Windows
boxes (both servers and end systems in offices) run by somebody who wouldn't
believe an Ethernet has anything other than a 1500 MTU if you stapled the
spec sheet to their forehead?

For that matter, what releases of Windows support setting a 9K MTU?  That's
probably the *real* uptake limiter.

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