[Bridge] Need help: bridge does not flood ethernet frame with mtu > 1500

CHOU Sovatha RD-CORE-ISS sovatha.chou at francetelecom.com
Mon Mar 14 02:03:40 PST 2005


Hello all,

On my previous post I maked a mistake on my analyze. The bridge forward
well any kind of frames it received. The problem was I used frame with
VLAN. On Is-Is hello frame, the frame has an MTU greater than 1500
because of the 4 bytes VLAN enclosed. So all Is-Is hello packets were
dropped.

The architecture used is:

	eth1 (real physical interface) ---- BRIDGE ---- uml0 (tuntap
interface to UML)

I solve the this problem with the real interface by changing the mtu to
1520. But the issue remains on the virtual side. I can not modify the
tuntap's MTU to something greater then 1500. 

Does someone know how I can do to change the mtu of the tuptap device ? 

In advance thanks.

Sovatha

PS: The MTU must not be lower than 1500 because the simulated Is-Is has
to form topology with a real router where the interface MTU can not set
to a value lower than 1500.
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