Network failure

I'm getting unreliability in the network system - when under heavy load it will tend to lose connection with the outside world. Network interrupts are still being received, but nothing's getting through to the actual stack. Just restarting the network (rcnetwork restart, rcroute restart) lets me resume, and we now have a watchdog script running to do this, but it's annoying all the same. Anyone else getting this/got a fix? -- Rachel