A router will have many common interfaces and a number of optional interfaces that can be installed (these options will be dependent on the type of connections the router will be connected to eg ISDN, ASDL, T1/E1, Fast Ethernet or Gigabit Ethernet.)
Common router interfaces that will be on most routers are;
Console – This allows a user to connect to the router to monitor and program it. The console connection typically uses a rollover cable and connects to a PC via a serial connection. A terminal emulator such as putty or HyperTerminal is then used to connect to the router.
The screenshot below shows a PC having being connected via putty to a router.
AUX- This allows a user to connect to the router via a telephone line to perform monitoring and programming actions remotely.
Almost all routers will come with a type of Ethernet connection, this may be fast Ethernet (A typical port might be named FA0/0) This allows local area network devices such as hosts or switches containing many hosts to connect to the router.
Some routers may also (or alternatively) have a GigaBit Ethernet interface (GI0/0)
The most common Wide Area Network port of a router will be some form of serial interface. This connects to telecommunications equipment owned by a telecoms provider to connect to T1/E1 internet connections.
Routers can be used to segment a Local Area Network (LAN) by connecting different networks together, this makes the network more efficient by dividing the collision domain, cutting down on collisions and making the network more efficient, however routers are more commonly deployed as interconnecting devices over a WAN. They can be connected to LANs via the Ethernet interface and to WANs via the serial interface.