Odd network behaviour

[Simon Bland <angel@khaosse.net>]

I've recently upgrade my desktop and I've noticed some odd behaviour
with my network since then.. My machine is currently acting as the
gateway for a small home LAN, I'm running dnsmasq to handle the
forwarding and iptables for the firewall.

The odd behaviour is that any time my machine is under load the network
cuts out all together, or only about 1 in 50 or so packets gets back
from a ping.

I should probably clarify that a little, the LAN side seems to work
fine, it's the PPP interface thats locking up when I'm under load, which
is sorta strange being that the modem is about the only thing I didn't
change.

I'm using a 3Com US Robotics 56K. Kernel version 2.4.19. With the PPP
stuff build as modules. I'm not 100% sure if it is something to do with
the new system, as I also upgraded from 2.4.18 to 2.4.19 when I did the
hardware change.. I know I really should test that, and I will, but if
anyone has any ideas as to what might be causing this problem some
advice would be greatly appreciated.

Thanks.