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
In case you are going to redistribute the loopbacks instead of advertising these loopbacks with the network command then they will be advertised with the /24 even without the ip ospf network point-to-point command under the loopbacks
R4#show running-config interface lo0
Building configuration...
Current configuration : 62 bytes
!
interface Loopback0
ip address 10.1.0.1 255.255.255.0
end
R4#sho
R4#show run
R4#show running-config | sec router
router ospf 1
redistribute connected subnets
network 192.168.24.0 0.0.0.3 area 0
network 192.168.34.0 0.0.0.3 area 0
R4#
R1#show ip route 10.1.0.0
Routing entry for 10.1.0.0/24
Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric 20
Last update from 192.168.12.2 on Ethernet0/0, 00:16:54 ago
Routing Descriptor Blocks:
* 192.168.13.2, from 10.4.0.1, 00:16:54 ago, via Ethernet0/1
Route metric is 20, traffic share count is 1
192.168.12.2, from 10.4.0.1, 00:16:54 ago, via Ethernet0/0
Route metric is 20, traffic share count is 1
R1#
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
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.
Fully correct, the loopback would be reachable however it would advertise /32 instead of a /24. So there is no need to correct any configuration, changing it would only advertise different mask, but you would not be able to reach any other interface in the actual advertised network. Stupid question.
I believe it is because the route is advertised as a /32 (since OSPF does that by default for loopback interfaces). In order for it to be advertised properly as a /24, the configuration shown in A should be done.
Having the route advertised as a /24 or /32 really doesn't matter - 4.4.4.4 would be reachable in both cases. The phrasing of the question is absolutely terrible...
Point is that if you configured the loopback as a /24 is because you need the whole /24 to be advertised as well (for other purposes like NATed addresses). Otherwise you would configure the loopback as /32.
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