kernel-2.6.17: DHCP fails with stock kernel image, works with roll-my-own kernel
I have been rolling my own kernels on this machine (Thinkpad A21m, Debian testing) for a long time, but really don't need to anymore, so I thought I would install the stock kernel images.
Alas, with the stock images (both linux-image-2.6.17-2-686 and linux-image-2.6.18-1-686) my network interfaces (both mini-PCI and PCMCIA) refuse to play with DHCP. If I run tcpdump on the DHCP server end, I can see the DHCP request coming in from my machine and the response going out. But tcpdump running locally on the A21m does not see the response from the server at all.
But, if I boot back into my home-made linux-image-2.6.17-a21m.26, everything works fine. The only difference is which kernel has been booted, all other hardware and software configuration is identical. There are no interesting errors in syslog, the only visible ailment is that DHCP times out (and tcpdump indicates the response packets are disappearing into the void somehow).
This installation has been running for years, so I guess I could be being bitten by some old and stale configuration file, but I haven't got a clue how to proceed.