Cisco Router Interface Naming Convention

On Legacy routers like 2500 series routers the interfaces are fixed and the name of the interfaces will always be the same. However, on newer routers like 2600, 2800 and 2900 series routers, interfaces can be modular. Here the interfaces are cards (modules) that can be “plugged into” the router in different slots. Some of these interfaces are on WAN interface cards (WIC) and some are on Network Modules (NM).

You have to always keep in mind that Ethernet means old and outdated 10 Mbps Ethernet. Fast Ethernet means 100 Mbps Ethernet and Gigabit Ethernet means 1000 Mbps Ethernet.

In new routers the interface name designates the physical location of the Layer 3 interface within the chassis. Interface name is composed of a three parts, formatted as slot number (The slot in which the interface module is installed.) /0 (The number of the interface module for this port. When the module consists of a single card, this number is always 0) / port number (The port number on the interface module. The port numbers always begin at 0 and, when facing the rear of the switch router, are numbered from the left port to the right port. The number of additional ports depends on the number of ports available on the interface module.).