Interface Commands

Interface configuration is one of the most fundamental aspects of getting a router online. There are many kinds of interfaces, corresponding to different physical media and lower-level protocols; some of the interface types are listed in Table 5-1. For the most part, each media type has its own configuration commands, although a few commands are common to all interfaces. The interface is where much of IP configuration takes place: it's where you set addresses and netmasks and specify how the interface interacts with the routing protocol you have chosen.

Table 5-1. Interface types

Type	Description
async	Async lines are for modem dial-in and dial-out connections. The AUX port is an async line. Terminal servers have numerous async lines for modem connections.
atm	ATM (Asynchronous Transfer Mode) interfaces are used for connections to an ATM switch. This includes DSL connections.
serial	Serial ports are often connected to CSU/DSUs for point-to-point leased lines (56k, T1, etc.).
ethernet	Ethernet ports supporting 10 megabits/second.
fastethernet	Ethernet ports supporting 10 and 100 megabits/second.
gigabitethernet	Gigabit Ethernet ports supporting 10/100/1000 megabits/second.
bri	BRI (Basic Rate Interface) for ISDN (2B + D service).
tokenring	Token ring network interfaces.
fddi	Fiber Distributed Data Interconnect.
hub	A hub that is built into the router and treated as an interface.
hssi	High-Speed Serial Interface. Supports speeds up to 52 Mbps.
loopback	A virtual interface on the router.
null	Bit bucket interface. Anything sent to this interface is discarded. Used for simple route filtering.
pos	Packet over SONET interfaces.
vlan	Virtual LAN interfaces.