using non-default MTU for some hosts

[Martin P. Hellwig]

Matthew Dillon wrote:
:> Thanks for the prompt response! I was hoping, it would also work the
:> other way... Can you give a quick example, please? Let's say, two
:> BSD-hosts: "mi" and "pandora" have the jumbo-frame cards and want to use
:> them fully. The rest of the network -- say 172.21.128/20 -- can only use
:> the 1500-long frames.
:>
:> What are the commands to enter on both machines? I figure, I must start
:> with something like `ifconfig em0 mtu 8000' on each one, but then, how
:> do I tell them, that they should limit the mtu to 1500 in almost all
:> cases? Thanks again!
:
:You'd probably configure normally with ifconfig, and then use 'route' to
:create a static route to "mi" that uses the different MTU size, and then
:again for "pandora".  i.e. 1500 is the default, and 8000 is the special
:case.  I'm saying this without having tried it, of course.
:
    It's worth a shot.  I'm not sure if the interface mtu is a cap or just
    a suggested default.
To my understanding the value set in MTU is the starting frame size and 
will decrease until it fits the pipe to the endpoint.

--
mph