A.1 Interface Identification

CISCO routers have specific names for individual interface types, for example, Ethernet for an Ethernet interface or Serial for a serial interface. The same applies to lines. Console or simply con used for a console (marked sometimes as CTY), aux for auxiliary asynchronous interface, tty for asynchronous lines, and we should not forget to mention vty for network terminals (or pseudo terminals, if you wish to use the UNIX terminology) to which Telnet will be connected via the network.

Since the router has several interfaces, we always have to specify not only an interface’s name, but also its number that is set by the hardware configuration. For example, if we have two serial interfaces, then one will be labeled as Serial 0 and the other as Serial 1. Knowing which one is 0 and which one is 1 also depends on the hardware configuration (more information can be found in the hardware manual). We should not forget to include the number even if the box has...