300-410 Exam - Question 70

Question

Refer to the exhibit. Which set of commands restore reachability to loopback0?

Examice · Accepted Answer

In OSPF, loopback interfaces are treated as host routes by default, meaning they are advertised with a /32 mask. This can cause issues if the network requires the loopback interface to be advertised with its configured subnet mask, such as /24 in this case. To restore reachability with the correct subnet mask, the command 'ip ospf network point-to-point' should be applied under the loopback interface. This command forces OSPF to advertise the loopback interface with the configured mask instead of the default /32 host route. Thus, the correct set of commands to restore reachability to loopback0 is option A.

palihaff · Answer

I understand the answ, but please, somebody explain, to me how the original config can make 4.4.4.4 unreachable. Thanks !

Carl1999 · Answer

Loopbacks are considered host routes in Open Shortest Path First (OSPF). 
To make OSPF advertise the loopback subnet as the actual subnet with the loopback mask, instead of as host route /32, issue the ip ospf network point-to-point command under the loopback interface.
For more information, refer to the 9.1. Interface States section of RFC 2328.

heeeeyajoke · Answer

I have tested the lab, i could still reach the loopback, OSPF advertised a /32 route for the loopback by default. But i would go for the option A for the exam

anaisa_goncalves · Answer

Here's the explanation:
https://networkengineering.stackexchange.com/questions/13099/why-do-we-use-ospf-point-to-point-networks-for-loopbacks

XBfoundX · Answer

The network type broadcast is not accepted in the loopback interfaces.

R4(config-if)#ip ospf network broadcast
% OSPF: Invalid type for interface Loopback0

So for allow to exchange the loopback as not as a /32 network the only option that we have is use the command ip ospf network point-to-point command under the loopback interface

SeMo0o0o0 · Answer

A is correct

300-410 Exam - Question 70

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