Configuring serial interface in cisco router

Router Serial Interface Configuration

In this step by step tutorial you will learn how to configure serial interface on Cisco router. You will learn how to set clock rate, bandwidth and IP address on serial port of router.

There are various interfaces present on a router. Each interface has its own applications. Ethernet is used in applications where data has to be transmitted at high speed and the distance between the routers is less.

 The Ethernet transmits the data parallel and hence achieves high speed. Though the Ethernet transmits data at high speeds it has a limitation that the Ethernet cannot transmit data over long distances. To overcome the problem of transmitting data over long distances, serial interfaces are used.

Serial interfaces can be connected using the cable V.35 DTE and DCE cables. The interface to which DTE end is connected act as Data Terminal Equipment and the end where DCE connected acts as Data Communication Equipment.

 Data Communication End provides clock rate and allocates bandwidth to the Data Terminal Equipment. To know whether the serial interface on the router is a Data Communication End or Data Terminal End, we can use the command

CISCO-ROUTER# show controller <interface name and number>

The above command provides you with the information about the interface whether it is a DCE or DTE.

Configuring Serial interface DCE end:

CISCO- ROUTER> ENABLE (To enter into privileged exec mode)

CISCO-ROUTER# CONFIGURE TERMINAL (Allows to enter global configuration mode)

CISCO-ROUTER(CONFIG)# INTERFACE s0/0 ( Opens interface configuration mode and allows an administrator to configure s 0/0. ‘s’ represents Serial.)


CISCO-ROUTER(CONFIG-IF)# clock rate 64000 (assigns clock, helps in synchronization)

CISCO-ROUTER(CONFIG-IF)# bandwidth 64 ( Sets the bandwidth)

IMP: Clock rate and Bandwidth are assigned at DCE end.




Configuring Serial interface DTE end:

CISCO-ROUTER1(CONFIG)# INTERFACE s0/0 ( Opens interface configuration mode and allows an administrator to configure s 0/0. ‘s’ represents Serial.)





Clock and bandwidth are provided at the Data Communication Equipment (DCE). If the clock is not provided at the Data Communication Equipment, the data is not transmitted between the two serial interfaces.

The serial interfaces may be physically up but they are logically down. They are logically turned on only if appropriate clock rate and bandwidth are provided at the Data Communication Equipment.

To know whether the interface is up, physically or logically, use the command shown below

CISCO-ROUTER# show interface serial<number>

Serial interfaces use the either HDLC or PPP to encapsulate or format the data. HDLC stands for High-Level Data Link Control and does not support authentication.

Hence, we use Point to Point Protocol (PPP). PPP uses Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP) to provide authentication.

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