EIGRP router Id is a 32-bit unique identifier which identifies the router in EIGRP domain. The router ID (RID) is represented in the same way as represented 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 then 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, the router selects the highest IPv4 address of any of its loopback interfaces.
- If no loopback interfaces are configured than router selects the highest active IPv4 address of any of its physical interfaces.
A loopback address is a virtual interface, which is automatically changing the state to up when configured. The interface not required to include 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. Though in 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 router configuration mode. When configure EIGRP router ID with this command it takes priority over any loopback or physical interface IPv4 addresses. Now lookit the figure 1, the same topology we have used for router command. Let’s see the configuration EIGRP router ID on all three routers.
R1(config)#router eigrp 1
R1(config-router)# eigrp router-id 184.108.40.206
R2(config)#router eigrp 1
R2(config-router)# eigrp router-id 220.127.116.11
R3(config)#router eigrp 1
R3(config-router)# eigrp router-id 18.104.22.168
The IPv4 address configured as router ID is any 32-bit number displayed in dotted-decimal notation. We can configure any IPv4 address as 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 IPv4 loopback address and IPv4 address of the physical interface as router-ID. But the loopback address as router-ID has an advantage over IPv4 address of the physical interface. The loopback interface cannot fail like physical interface. Because there are no cables or adjacent devices on which the loopback interface depends for 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, then 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 any active routing protocol processes, including both EIGRP and OSPF. The command also displays different types of output specific to each routing protocol.