Every IP interface (either physical, virtual or ATM-subinterface) had its own name, with the suffix corresponding to the equipment the interface belonged to, and a distinguished name describing the interface. The interface ordinal numbers corresponded to the ones in the equipment configuration and usually started with 0.

Overview:
Loopback (2 or more):                                        lo0 and lo1
Fast-Ethernet in some VLANs (1 or 2):            fe0, fe1
Giga-Ethernet in some VLANs:                         ge0

POS or ATM interfaces for connections to other pops, called by the PoP name on the opposite side of the network link: the interface in the UK router connecting to the FR PoP is called fr.uk6.uk.net.sixnet.org.

Example:

Loopback interface on the United Kingdom router: <lo0.uk6.uk.6net.org>