Strange crossplatform network problem

This is not a specific Win 7 problem but it's involved so here goes!

I have four machines all connected to a switch, two wirelessly and two
wired. The router is wired also to the switch.
The two wired machines, one a laptop and one a desktop, both running Windows
XP, one wireless laptop is running Windows 7RC and the other Netbook,
Ubuntu.
Occasionally, like this afternoon, one of the wired machines and BOTH the
wireless machines will suddenly drop internet access, although access to
shared drives on the LAN is still there, yet the one XP wired laptop machine
does NOT drop internet access. The only way of returning access to the three
machines that have dropped it is re-boot the router, causing hassle to the
one machine that is still on the internet.

Can anyone tell me any reasons why this hugely irritating and totally
illogical scenario might come about?

A wireless switch? I'm assuming you mean some sort of WAP whose own router functionality is disabled?

It sounds like the router (the one you're rebooting) is at fault. It may be somehow getting its ARP or NAT session table entries mixed up. Whatever the reason, the fact that it happens for more than one machine concurrently almost proves involvement from the common componentry - either the router or the "switch". Since local access from client to client is still functional, that would seem to rule out the switch, which leaves the ... router.

H2SO4 said:

A wireless switch? I'm assuming you mean some sort of WAP whose own router functionality is disabled?

It sounds like the router (the one you're rebooting) is at fault. It may be somehow getting its ARP or NAT session table entries mixed up. Whatever the reason, the fact that it happens for more than one machine concurrently almost proves involvement from the common componentry - either the router or the "switch". Since local access from client to client is still functional, that would seem to rule out the switch, which leaves the ... router.

hhmmm, two DCHP servers active maybe?

squonksc said:

hhmmm, two DCHP servers active maybe?

Possibly, though that wouldn't be my first guess personally. The lease durations would be unlikely to expire concurrently on three clients. Perhaps the OP's into synchronised machine (re)booting and that's why they all obtained leases within a minute of each other

Also, if the second DHCP server's range was completely subnet-incompatible, local connectivity to the 4th box would fail (the one which can still access the internet).

H2SO4 said:

squonksc said:

hhmmm, two DCHP servers active maybe?

Possibly, though that wouldn't be my first guess personally. The lease durations would be unlikely to expire concurrently on three clients. Perhaps the OP's into synchronised machine (re)booting and that's why they all obtained leases within a minute of each other

Also, if the second DHCP server's range was completely subnet-incompatible, local connectivity to the 4th box would fail (the one which can still access the internet).

We definitely need more info on the router, the switch, the network cards, ISP, ADSL? Cable? p2p apps, voip maybe?