[Netkit.users] Issue with vlan/mtu

Cedric Foll cedric.foll a laposte.net
Gio 22 Nov 2007 23:35:40 CET


I'm trying to realise a vlan TP with netkit.
Here is my lab:

pc1 --eth0=A=
pc2 --eth0=B=

bridge --eth0=A --eth1=B --eth2=C

fw --eth0=C

Then i create VLAN 100 and VLAN 200 on fw/eth0 and bridge/eth2
Then i bridge (eth0 and eth2.100) and (eth1 and eth2.200).
I give to eth0.100 on fw and to eth0.200.
Finaly i setup the default gateway on pc1 et pc2.

I ping pc2 from pc1, it's works.

Next i try to do a wget and i start to have MTU issues:
IP truncated-ip - 4 bytes missings...

So the 802.1q link between bridge and fw have a problem.
If i force the mtu to 1496 on pc1 or pc2 everything work but i don't
want to force all my stations with a new mtu.

So what can i do ?
-bridge may fragment ? how ?
-bridge may send a path mtu to station ? (it doesn't send anything)
-is it a netkit/kernel issue ? Some websites speak about this kind of
issue with mtu using 802.1q links on few networks cards


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