If routers in a single area are configured with the same priority value, what value does a router use for the OSPF Router ID in the absence of a loopback interface?a)The lowest IP address of any physical interfaceb)The highest IP address of any physical interfacec)The lowest IP address of any logical interfaced)The highest IP address of any logical interfaceCorrect answer is option 'B'. Can you explain this answer?

Question

Answer

Explanation:

In OSPF (Open Shortest Path First) routing protocol, each router is assigned a unique Router ID (RID) to identify itself. The Router ID is a 32-bit value represented by either an IPv4 address or a 32-bit number.

When configuring OSPF, it is best practice to assign a loopback interface as the Router ID. The loopback interface is a virtual interface that is always up and running, regardless of the status of physical interfaces. It provides a stable and unique identifier for the router.

However, if there is no loopback interface configured on a router, OSPF will use the highest IP address of any physical interface as the Router ID. This means that the router will examine all of its physical interfaces and select the one with the highest IP address to be used as the Router ID.

Reasoning:

The reason for using the highest IP address of any physical interface as the Router ID in the absence of a loopback interface is to ensure stability and consistency in the network. The Router ID needs to be unique within the OSPF routing domain to avoid conflicts and inconsistencies.

By selecting the highest IP address of any physical interface, the router is using a value that is less likely to change. Physical interfaces are typically assigned static IP addresses, and their addresses are less likely to change compared to logical interfaces.

Using the highest IP address of any physical interface as the Router ID ensures that even if the router reboots or interfaces go down and come back up, the Router ID remains constant. This stability is important for OSPF to function properly and maintain network connectivity.

Additionally, the highest IP address of any physical interface is a logical choice because it represents the router's external interface, which is typically connected to other routers in the OSPF area. This allows for better network convergence and consistent routing table calculations across all routers in the area.

Conclusion:

In the absence of a loopback interface, OSPF routers in a single area will use the highest IP address of any physical interface as the Router ID. This ensures stability, consistency, and uniqueness within the OSPF routing domain, promoting efficient routing and network convergence.

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