How to Configure an IPv4 Loopback Interface
The IPv4 loopback interface is logically configured internally in the router. In this lesson, we should discuss this interface configuration, but at this stage, it is necessary to know the Pv4 interface configuration before the IPv4 loopback interface configuration.
I discussed the IPv4 interface configuration in one of my previous lessons. The address of the lesson is Cisco Router Interface Configuration.
So, let’s come to the topic. As I said, the loopback interface is logical and cannot be physically found on the router. Therefore, it cannot connect to any other device physically. Its state is always up when a router is functioning.
It is instrumental in troubleshooting and managing a Cisco router because it ensures that at least one interface is always available for management. For example, we can use a loopback for testing purposes and the loopback interface instead of a physical interface address for routing purposes.
Usage of Loopback Interface
We can use the loopback to recognize the device because the address of the loopback never changes; therefore, it is the preferred method for identification of the router.
The Loopback Interface is always up and allows Border Gateway Protocol (BGP) neighbours between two routers to stay up even if one of the outbound physical interfaces connected between the routers is down. Loopback interfaces are also the termination points for Remote Source-Route Bridging and Data-Link Switching Plus.
The OSPF also uses the loopback address to determine protocol-specific properties for the device or network. Additionally, ping and mpls need a loopback address to function correctly. We can also apply stateless firewall filters to the loopback address to filter packets originating from or destined for the Routing Engine.
The configuration of the Loopback interface
We can enable multiple loopbacks on the Cisco router. Each loopback requires a unique IPv4 address. The number is different for routers, but it starts at 0 and goes up to billions.
