Examine the following exhibit. What is the router ID for R1?

Examine the following exhibit. What is the router ID for R1?

R1# configure terminal
R1(config)# interface loopback 0
R1(config-if)# ip address 192.168.1.253 255.255.255.0
R1(config-if)# interface ethernet 1/0
R1(config-if)# ip address 192.168.1.1 255.255.255.0
R1(config-if)# exit
R1(config)# router ospf 1
R1(config-router)# network 10.0.0.0
R1(config-router)# end
R1#

• 10.0.0.0
• 1
• 192.168.1.253
• 192.168.1.1
• The router ID is currently unassigned.

Explanation: OSPF follows a specific three-step hierarchical process to select a Router ID (RID) when the routing process starts:

1. Manual Configuration: It first checks for a manually configured ID using the router-id command under the OSPF process.
2. Loopback Interface: If no manual ID is configured, it selects the highest IP address of any active loopback interface.
3. Physical Interface: In the absence of a loopback interface, it selects the highest IP address of any active physical interface.

In the provided exhibit, there is no manual router-id command configured within the router ospf 1 block. However, a loopback interface (Loopback 0) is configured with the IP address 192.168.1.253 [Exhibit]. Because a loopback interface exists and its IP address is numerically higher than the physical interface IP (192.168.1.1), OSPF automatically selects 192.168.1.253 as the Router ID for R1.

Note that an interface does not need to be actively participating in OSPF via a network command to be considered for the Router ID selection; it only needs to be in an active (up/up) state.

Related exam: Modules 8 – 13: Checkpoint Exam: Network Routing Answers (CCNP ENCOR v9)