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