It seems like /etc/iftab is gone on (x)ubuntu 7.10.
In fact, it is… but the mapping is now handled by udev.
Update: /etc/iftab/ is missing on (x)ubuntu 8.04, 8.10, 9.04 and 9.10 as well.
So if you want to assign persistent names to devices, just fire up an editor with the file
-$ sudo nano /etc/udev/rules.d/70-persistent-net.rules net.rules
and you will see something like this:
Change the entries of the appropriate macs to something you like. I changed the name of my wired lan (eth0 above) to lan1 and my wireless lan(eth1 above) to wlan1 as I like to start counting with one.
