torubles with "Jumbo frames" in 2.6.x

[Brane2]

Hi to all,

I have sevaral machines, connected in small network through 1 Gbit
Broadcom cards (Tigon3 driver).
When I set mtu to 8192, machines can't communicate anymore, until I
ifconfig down & ifconfig up at least one of the communicating sides.

I have also noticed that when I ifconfig down the card, my default route
vanishes and doesn't come back when I ifconfig up (when default route
goes through ifconfiged card)

Is this normal ?

Also, mtu on both communicating parties must be the same and module
obviously refuses to negotiate acceptable mtu for both communicating
machines.

I have three similar machines connected in a sort of a "Y" shape.
One machine is central server, connected to DSL, other two machines are
connected to sevrver directly (crossover Ethernet cable to server).

Machines are:

-Dual Opteron 240
-TYAN K8W motherboard
-2GB RAM,
-nVidia GF4 graphic ccard
- Ethernet cards on board and in PCI-X slots, based on Broadcom 5760
(Tigon3 driver)

-64Bit Gentoo Linux on all machines , two non-server machines are dual
boot. WinXP on one chokes on big MTU (it request mtu to be 8000 and even
then I have to ifconfig down/up card on server after each post of XP
machine). Win2K on other machine seems to be working fine on other
machine, though...

-kernel 2.6.8-rc3 and kernel 2.6.8-rc4 (on one leaf machine, not server)

Regards,

Branko