The Serial Connection is used to create a WAN connection with the help of a service provider who offers a dedicated leased line to its customers.
Business organizations buy leased lines to establish a WAN connection to connect with different offices and business sites that could physically be thousands of miles apart. Businesses have to pay for these leased lines according to the service availed. And accordingly, the service providers charge for this service i.e. based on the bandwidth they offer to their client organizations.
One of the connections used for a leased line is the Serial Connection in Cisco based networks. If we have Cisco routers on both sides of the network then the default encapsulation known as HDLC will be used by the Cisco routers. However, this will not work with other brands routers (i.e. with the non-Cisco routers) because this protocol is solely a Cisco proprietary.
If we want to establish successful connection with router of other vendor then we must configure the same data link protocol on both router. If there will be a mismatch then connection cannot be established and we will see the status of the interface as down under data link.
If we are configuring new cisco router then by default the data link protocol would be HDLC however if we are configuring old device then we should check the configuration and if there is a mismatch then we have to configure the same protocol on both routers.
Although HDLC works out of box on all cisco routers however it is not widely used because of its propetery nature and it does not provide much feature so PPP protocol is used by most organization. Even on cisco routers, organizations prefer PPP protocol over HDLC protocol due to its advance features and benefits.
In this lab, we will configure a Serial Connection between the routers. We will set up a clock rate at 56000, which will provide the speed of 56 Kbps. In a real world, the DCE side of the cable is configured by the service provider. Generally, the clock speed is configured according to the availability of the bandwidth speed that the service provider is offering.
The following lab uses a serial cable that will simulate a service provider. We will configure the clock speed on the router that has DCE side connected.
Serial interface configuration
Lab Tasks
1. Assign IP address to both routers and turn them on
2. Set clocking on DCE side, which is router 0
Lab Configuration
Task 1
Router 0
Router(config)#interface serial 0/1/0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# no shut
Router 1
Router(config)#interface serial 0/1/0
Router(config-if)# ip address 192.168.1.2 255.255.255.0
Router(config-if)# no shut
Task 2
Router 0
Router(config-if)# clock rate 56000