IP Unnumbered Explained

Hello Taha

Thanks for sharing your details concerning the topology you want to create. I have the following suggestions:

  1. Make sure that automation is indeed the best way to proceed. In some situations, using the CLI and simply copying and pasting is faster. For a single topology that doesn’t change much, automation will deliver limited benefits. If you want to reuse code for other devices on other topologies in the future, that’s different.
  2. If you want to use Python, I’d suggest you use tools like Paramiko instead of trying to build solutions from scratch. Paramiko is an SSH solution for Python.
  3. The ip unnumbered loopback0 works just fine, but has the following limitations:
    a) You can’t ping the physical interface since it uses the IP of the loopback interface.
    b) It doesn’t work on some devices. For example, on IOS 15, you get the following error:
R1(config)#interface gi0/1
R1(config-if)# ip unnumbered Loopback0
Point-to-point (non-multi-access) interfaces only
  1. In such a configuration, you will still have the same number of OSPF neighbor adjacencies.
  2. Concerning address space wastage, this only comes into play if you are using public IP addresses. WIth private addressing, this is not an issue. Even so, if you choose to, you can use /30 subnets which would keep wastage to a minimum.

I hope that responds to most of your queries. Rene has created a note in our new note repository about IP unnumbered. You can find it here:
https://publish.obsidian.md/networklessons/notes/OSPF+IP+Unnumbered

Also, if you’re interested in furthering your automation skills, take a look at our Python course.

I hope this has been helpful!

Laz