OSPF Loopback interfaces are treated as a stub host and will only have a 32 bit host route on the other devices no matter how the subnet mask is entered under the OSPF network statement.
We will explore how we can disable this default behaviour using a few methods.
As you can see, R4 is configured with IP address 192.168.1.4 and R5 with 192.168.1.5.
We have loopback interfaces added with /24 subnet masks on R4 and R5
We are running basic OSPF Configs as follows…
This is what we are seeing on R4 and R5 and we expected this…
Now we will try the first method, this is to set the OSPF Network type to point-to-point under the interface configuration mode.
As you can see this works, and now we are seeing the whole /24 Range…
Second option we got is to redistribute the connected network with the with the redistribute connected subnets under the Router OSPF configuration mode.
When it comes to redistribution, try not to go wild and it is always a good idea to create route-map to point out what you want redistributed.
The third option we have is to use the Area Range command. To accomplish this, we will need to add a few more Loopback interfaces on R4 then we will use the area x range command to summarise it.
When we add the loopback interfaces into OSPF, it is still showing it as a /32 Host route…
Now, we will use the Area 1 Range command to summarise it on R4. Once it is done, we can now see the end result.
Note: The above Loopback networks have been added into Area 1 under the Router OFPF configuration.
These are the three method I know of when it comes to disabling the /32 host route on OSPF Loopback Networks… 🙂