[Netkit.users] Issue with vlan/mtu

Cedric Foll cedric.foll a laposte.net
Ven 23 Nov 2007 00:43:15 CET

> Hold on, you mean that the Linux box is VLAN unaware, and the the IP
> packet transits towards a VLAN aware segment ??

PC1, right. But it's not his problem. The link between PC1 and Bridge
isn't a 802.1q
I have this:

If i force PC1 with a mtu of 1496 it works but i don't want to solve
the problem there.

> In this case OF COURSE the first switch at the edge of the VLAN aware
> segment of the Network will fragment the packet if HIS MTU is not
> bigger than 1500. This is the normal behaviour as far as I know.

But bridge doesn't fragment anything (maybe i have to do a echo 1 >
somewhere in /proc...)

> The REAL solution is having a MTU of  at least 1504 bytes in the VLAN
> aware network

I've already tried it:
ifconfig eth2 mtu 1504 on Bridge
ifconfig eth0 mtu 1504 on FW but doeesn't solve anything.

> There is not ICMP message for indicating that IP packets are being
> fragmented. The only case is when the Dont' Fragment bit is set, and
> packet is dropped, in that case you get back an ICMP

Right. Is it an option in /proc which force all packet with this bit ?

Thanks for you help.

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