Curious thing some of you may run into. I tried to plug a Ubuntu Karmic 9.10 linux machine into my router running Tomato 1.27, but it failed. Turns out you need to disable IPv6, since Tomato does not support it.
Right click on NetworkManager panel applet.
Choose Edit Connections…
Choose “Audo eth1” (or whichever port)
Press “Edit”
Select IPv6 tab
Set Method to “Ignore”
Click Apply