North American Network Operators Group

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Re: Ethernet NAPs (was Re: Miami ...)

  • From: Mikael Abrahamsson
  • Date: Thu Aug 23 02:34:17 2001

On Wed, 22 Aug 2001, RJ Atkinson wrote:

> Only devices exchanging frames with each other need have the same
> MTU.  One could easily imagine one 802.1q VLAN with MTU N and
> a different 802.1q VLAN with MTU Y all on the same switch,
> to give a trivial example.  Some exchanges already use VLANs
> with their GigE switches for a variety of business reasons.

Which is exactly how we've done it with our testbed here in Stockholm. One
VLAN where you are REQUIRED to handle 4470 MTU to be able to join, and one
MTU 1500 vlan. There are some equipment that'll fragment IP when doing L2
forwarding to a lesser MTU port (FE for instance) (one of the old
Cabletron companies) just like the old DEC gigaswitches used to do, but I
prefer to have everybody in the same L2 domain talk the same size MTU.
Seems much cleaner, and most vendors support at least 4470MTU on their
GigE ports these days.

Mikael Abrahamsson    email: [email protected]