I have a network at home which is bridged with a WLI-TX4-G54HP.
On the bridged segment there are 3 computers and a NAS, All the computers run Ubuntu 10.10 and have been happily working with this and other earlier versions of Ubuntu for a long time. I have just upgraded one of my machines (TEST) to Ubuntu 11.04 and have encountered a strange problem.

The bridged section is connected via the Buffalo WLI-TX4-G54HP ethernet converter which in turn connects to the rest of the network through my wireless router a Buffalo WBMR-G300N.

Now after the upgrade the test machine had an IP address which it must have got from the via DHCP. but the test system will not connect across the bridge. I can ping anything this side of the bridge but cannot ping devices on the other side, including the gateway and vice versa. The other non upgraded PCs will ping across the bridge

I tried to install Mint 10 and got exactly the same behaviour.

I then got out my very long CAT5 cable and ran it from the switch directly to the wireless router and it works perfectly, this seems to me a perfectly valid work around, however, STMBO for some reason does not. (which is why the lan was bridged in the first place).

Reverted to Ubuntu 10.10 and the bridge works again.

I am totally out of ideas, nothing else was touched. So out of frustration I have now stripped the network out and set it up bit by bit to see if I can make any difference and bought a new Gigabit NIC for the test machine so it matches the other machines.

Will see if any of this works