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Re: MAE-EAST Moving? from Tysons corner to reston VA.
From: michael.dillon () gtsip net
Date: 19 Jun 2000 10:40:14 +0100


On Sat, 17 June 2000, "Richard A. Steenbergen" wrote:

What is the largest MTU that you can use across a GigE fabric?

I think this would be extremely foolhardy. The common number that all
those using jumbo frames should support is 9000 bytes (not 9k aka 9216).
This would probably need to be a condition of using GigE at the NAP,
in order to achieve any kind of common support, and you're eliminating
some vendor gige support (assuming their network can even carry the 9k
packets TO the nap without requiring even more work and possible
problems).

I really should have worded that question more carefully. What I meant was, what is the maximum MTU that is supported 
by all GigE manufacturers and thus can be guaranteed to work without fragging across any arbitrary GigE fabric? I was 
under the impression that the answer is 1500 because not all vendors support larger MTUs.

And the implication is that GigE (in general) is not suitable for a public exchange fabric because it will introduce 
fragging in packets which are encapsulated (tunnelled). Of course, it would be possible to choose GigE equipment 
carefully and to configure it correctly to avoid this downside. But it seems to me that it is essential for any 
exchange point fabric or private peering link or IP backbone to support MTUs larger than 1500 edge to edge.


---
Michael Dillon   Phone: +44 (20) 7769 8489   
                 Mobile: +44 (79) 7099 2658
Director of Product Engineering, GTS IP Services
151 Shaftesbury Ave.
London WC2H 8AL
UK



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