Last Updated on July 31, 2021 by Admin 1
With respect to modifying an OSPF router ID to a loopback address, which of the following statements are true?
- OSPF is not as reliable if a loopback interface is configured.
- Using a loopback address avoids wasting an additional IP address.
- A loopback interface is not always active, and it can go “down” like a real interface.
- The loopback address does not automatically appear in the routing table of neighboring OSPF routers, so it cannot be pinged from other routers unless you include it with a network statement on the router local to the loopback interface.
A loopback address does not automatically appear in neighboring routers’ routing tables, so it cannot be pinged for network troubleshooting.
A work-around for this problem is to add a network statement under OSPF that advertises the loopback address network so that other routers will know how to reach your loopback.
A loopback address is an IP address assigned to a loopback interface, which is a logical interface on a router that behaves like a physical interface. Their advantage is that, unlike physical interfaces, logical interfaces do not go down.
For example: Router(config)# interface loopback 0 Router(config-if)# ip address 172.17.1.1 255.255.255.0
In the example, a loopback IP address is used by OSPF to provide its router ID. This type of address is preferred because it is assumed to be more stable than a router ID tied to a physical interface. The traditional problem with a router ID tied to a physical interface is that if the physical interface were to go down, the router would have to change its router ID to some other value. That would cause the OSPF neighbor relationships to reset and change values in the link-state advertisements (LSAs), causing a disruption to the OSPF area.
With this consideration in mind, OSPF is more reliable when using a loopback interface than using a physical interface.
Using a loopback address does not avoid wasting an additional IP address. The address must still be unique.
A loopback interface is always active, and it cannot go “down” as a physical interface can.
Layer 3 Technologies
Configure and verify OSPF operations