Hi,

> How can I be sure that the 1400 value for the Mtu will be the good one ?

um, because its what you'll need to use to get it to work? ;-)

the Cisco will only do 1500 - but as you are using PPT and/or IPSec, your packets
to and from the PCs are now 1500+padding - 'jumbo' frames. which means that protocols
which cant handle this properly are being fubar'd. The Intel card is quite happy
to shove bigger packets through the network, the via is chomping them to 1500
automatically so you dont see the problem with that. there are various calculations
that can be done to find optimal MTU size for your deployment, generally its best to make sure
that the number is padded/divisable by 16

Alan