Strange problem with Linux networking

For some reason, I sporadically have problems with Linux networking,
although Windows works without any obvious problems. DHCP works. I
acquire a sane-looking address and the same connection details (DNS
server, default gateway, netmask). DNS lookups work, as the DNS is
within the subnet. However, routing packages through the gateway
doesn’t work on Linux. Ethereal shows me that my computer keeps
sending ARP requests for the gateway, which doesn’t answer. When I set
the MAC address for the gateway using arp —set, I get delays when I
try to access it, and no successful transmissions.

The strange thing is that it sometimes works, it sometimes doesn’t.
This morning and early this afternoon, I connected without problems.
Sometimes I manage to connect during the night. Possibly a
misconfigured computer joining the network? (I hope it’s not mine.
Then again, I successfully connect some of the time.)

Now, I know the gateway exists, because I can see traffic from it from
time to time—usually, very delayed ARP responses to _other_ people,
not to me. Could my MAC address be getting filtered on the server
side? I’m not sure. That requires some setup (unless they have an
automated firewall doing weird stuff) and doesn’t explain why I can
occasionally access the Net.

Very strange.

I don’t think it’s my computer’s fault, but I’m still annoyed.

Other packets are going through the gateway fine. Why don’t mine?

Wild speculation: perhaps the server has a Windows-biased virus that
won’t let uninfected hosts access the Internet… ;) So much for
Occam’s Razor, eh?

I miss the Internet.