This documents a few things I discovered while building a new Linux box with 3 network cards (a 3com, a tulip, and a 4-port realtek PCI router card). I installed a hardened Gentoo profile on the box using hardened-sources-2.6.14-r5 (the latest version available as of a couple of weeks ago). The card didn't work with the LiveCD drivers, so all the work was done using the tulip interface.
Upon booting the new kernel and loading the 8139too driver, the interface appears normal for the most part, except I couldn't get any traffic to pass, either over it or through it. The LEDs on the back (one for each port and one labeled Host) flash in a slow pattern "off-dim-bright.. off-dim-bright.. off-dim-bright.. " and, although the interface can be configured as eth0, vlan0, etc, the ethtool output shows no link and 10 Mbps/Half Duplex.
Forcing the card to 100 Mbs/Full seems to work and makes the LEDs settle down, but still no traffic in any direction. Moving the card to another machine with a 2.6.12 kernel resulted in a working switch, but no traffic yet *through* the interface to the host itself.
At that point I decided to try the DOS diagnostic utility from a boot floppy and the basic card diagnostics checked out fine (I didn't try any link partner tests). I checked out the EEPROM settings and decided to enable flow_control for both transmit and receive, then rebooted in Linux. Lo and behold it worked, both as a switch and a host interface. Yay!
However, I now need to try and patch a 2.6.12 kernel with Pax/GRsecurity...