True! But in some point of the network it may be necessary to make the MTU
1500. For example, if your data need to cross the Internet. The border router
in between your LAN and the Internet will have to fragment a large frame back
to a normal one to send it over the Internet. This router will just "die" if
you have a heavy load.
From: Fabrice Bacchella <fabrice.bacche...@orange.fr>
Sent: Tuesday, August 8, 2017 12:23 PM
To: Moacir Ferreira
Subject: Re: [ovirt-users] Users Digest, Vol 71, Issue 37
Le 8 août 2017 à 11:49, Moacir Ferreira
<moacirferre...@hotmail.com<mailto: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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