We have several machines with on board sis900 nic. Under heavy utilization it just quits working.. no traffic passes at all.
To fix it we have to do service network restart (redhat) and it works or ifconfig eth0 down and up works.
We tried several redhat 8 kernels 2.4.18, 2.4.20 with various patch levels and all have the same problem.
Haven't tried 2.4.21 yet but i looked at the source and there isn't any significant changes
this is reproducable so i'd be happy to test any patches :-)
If you need any information from the machines themselves let me know and i will reply back.