What is the effect when loopback interfaces and the configured router ID are absent during the OSPF Process configuration?
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A. B. C. D.D.
In OSPF (Open Shortest Path First) routing protocol, the Router ID (RID) is a unique 32-bit number that identifies each router in an OSPF network. The RID is used to uniquely identify the OSPF router within an autonomous system (AS).
A loopback interface is a virtual interface used to provide a stable IP address for the router. It is commonly used as the source interface for OSPF routing updates.
When configuring OSPF process, if both loopback interfaces and the configured router ID are absent, the OSPF process will still run. However, the router will select a router ID based on the following rules:
If there is no configured RID and no loopback interfaces are present, the router will select the highest active IP address on any of its up/up physical interfaces as the router ID.
If there is no configured RID but loopback interfaces are present, the router will select the highest IP address of the loopback interfaces as the router ID.
If there is a configured RID, the router will use the configured RID.
If multiple loopback interfaces exist with IP addresses, the highest IP address among the loopback interfaces will be chosen as the router ID.
If all of the above methods fail to produce a router ID, the OSPF process will not start.
Option A, "The lowest IP address is incremented by 1 and selected as the router ID," is incorrect.
Option B, "The router ID 0.0.0.0 is selected and placed in the OSPF process," is also incorrect, as the router ID is selected based on the rules mentioned above.
Option C, "No router ID is set, and the OSPF protocol does not run," is also incorrect as mentioned earlier.
Therefore, the correct answer is option D, "The highest up/up physical interface IP address is selected as the router ID."