show eigrp router id

EIGRP router ID is a 32-bit unique identifier identifying the router in the EIGRP domain. The router ID (RID) is represented in the same way as the IPv4 address. The router ID is used both in EIGRP and OSPF, while the role of the router ID is more significant in OSPF. EIGRP automatically selects the highest IP address on any active loopback interface as the EIGRP router ID. If there is no loopback interface, the highest IP address on any active interface is used. The criteria for EIGRP router ID in Cisco routers are the following:

• Configure the router-ID using the command “eigrp router-id <IPv4 address>in router configuration mode.
• If the router ID is not configured with the above command, it selects the highest IPv4 address of any of its loopback interfaces.
• If no loopback interfaces are configured, the router selects any physical interface’s highest active IPv4 address.

A loopback address is a virtual interface automatically automatically changing the state to up when configured. The interface is not required to be included in the EIGRP network using network commands. It is only required the loopback interface in the up/up state.

Usually, we configure router ID using the “eigrp router-id” command. However, some versions of IOS will accept the command router-id without specifying eigrp.

Configuring the EIGRP Router ID

We can configure the eigrp router-id command in router configuration mode. When configuring EIGRP router ID with this command, it takes priority over any loopback or physical interface IPv4 addresses. Now, look at Figure 1, which shows the same topology we used for the router command. Let’s see the configuration of EIGRP router ID on all three routers.

Router R1R1(config)#router eigrp 1 R1(config-router)# eigrp router-id 1.1.1.1 Router R2 R2(config)#router eigrp 1 R2(config-router)# eigrp router-id 2.2.2.2 Router R3 R3(config)#router eigrp 1 R3(config-router)# eigrp router-id 3.3.3.3

The IPv4 address configured as router ID is any 32-bit number displayed in dotted-decimal notation. We can configure any IPv4 address as a router ID except the 0.0.0.0 and 255.255.255.255. The router ID must be unique in the EIGRP routing domain.

Loopback Address Used as the Router ID

We can use the IPv4 loopback address and the IPv4 address of the physical interface as router IDs. However, the loopback address has an advantage over the IPv4 address of the physical interface. The loopback interface cannot fail like the physical interface because there are no cables or adjacent devices on which the loopback interface depends on being in the upstate. So, using a loopback address for the router ID can provide a more reliable router ID than using an interface address.

If the router ID is not configured manually and loopback interfaces are configured, then EIGRP chooses the highest IPv4 address from the loopback interfaces as the router ID. To enable and configure the loopback interface, use the following command.

Router(config)# interface loopback <number>Router(config-if)# ip address <ipv4-address subnet-mask

We can remove the router-id using the “no router eigrp” command if the router ID is manually configured with the eigrp router-id command. If the router dynamically selects the router-id, we cannot change it.

Verifying the EIGRP Process

We can verify the EIGRP process and router-id using the show ip protocols command. Figure 2 illustrates the output for R1. The show ip protocols command also displays the parameters and current state of active routing protocol processes, including EIGRP and OSPF. The command also displays different types of output specific to each routing protocol.