> Le 8 août 2017 à 11:49, Moacir Ferreira <moacirferre...@hotmail.com> a écrit :
> This is by far more complex. A good NIC will have an offload engine (LSO - 
> Large Segment Offload) and, if so, the NIC driver will report a MTU of 64K to 
> the IP stack. The IP stack will then send data to the NIC as if the MTU were 
> 64K and the NIC will fragment it to the size of the "declared" MTU on the 
> interface so PMTUD will not be efficient in such scenario. If all this takes 
> place in the server, then you get no problem. But if a standard router is 
> configured to support 9K jumbo frame in one interface (i.e.: LAN connection) 
> and 1500 in another (i.e.: WAN connection) then the router will be 
> responsible for the fragmentation.

That's happen only if the bit don't fragment is not set, otherwise router are 
not allowed to do that and send back a "packet to big" ICMP, it's called path 
mtu discovery. To my knowledge, it's usually set, and even mandatory on IPv6.

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