What is Loopback Interface in Cisco Router and How to Configure
The Loopback interfaces play a vital role in troubleshooting. When the circuit is down, the loopback interfaces isolate the fault on. Loopback interfaces will go down only when then the router is down.
Unlike physical interfaces, Fast Ethernet and Gigabit Ethernet, the loopback interface is a virtual or logical interface or a software interface present in the Cisco routers. The software or virtual interfaces do not have any hardware components and these interfaces are independent of the state of any physical interface.
Any information or packet sent out through loopback interface is received immediately by the same loopback interface. The loopback interface will not go down unless an administrator gives the command shutdown or router is manually down.
Physical interfaces can go down or manually disabled for maintenance. As the interface is down, the other routers in the network cannot communicate with this router. We can overcome this issue by configuring a loopback interface. The IP address assigned and advertised over the network, the loopback interface is used to communicate with the router whose interfaces are down.
The Loopback interfaces play a vital role in troubleshooting. When the circuit is down, the loopback interfaces isolate the fault on. Loopback interfaces will go down only when then the router is down. Loopback interfaces are automatically turned on immediately after configuring the interface on a router. We can also use the ping command to verify if a router IP stacks working properly.
The loopback address is used to access the router for management. The loopback address is used by OSPF as router ID to stabilize the process.
They help to select, designated router and Backup Designated router when the routing protocol OSPF is configured in the network. Loopback interfaces can establish a telnet session from router console port to the auxiliary port when all physical interfaces are down.
The Cisco router ATM has two types of router interfaces
i. Loopback diagnostic
ii. Loopback line.
This loopback interface helps an administrator to determine if the interface configured is working properly or not.
Loopback line helps the administrator to find out if there is a problem from the service provider end.
To configure loopback interface, use the commands listed below
CISCO-ROUTER> Enable (Enters Privileged EXEC mode)
CISCO-ROUTER# configure terminal (Administrator enters global configuration mode)
CISCO-ROUTER(config)# interface loopback 0 (Enters interface configuration mode)
CISCO-ROUTER(config-if)# ip address 18.104.22.168 255.255.255.0
CISCO-ROUTER# copy run start
Cisco router automatically makes loopback interface active that is the loopback interface is removed from shutdown mode. A console message is displayed. The console message states that the interface is turned up. Cisco provides many loopback interfaces ranging from 0- 2,147,483,647.
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