🎥Keeping up with the Pepelnjakᣵ — OSPF over unnumbered interfaces for SROS

Running OSPF over unnumbered interfaces using SROS and Containerlab

Another week, another Netsim-Tools release 😩 One would think that a “reduced scope of activities” and Irena leaving would slow things down, but…The “s” (exponential) in the title reflects my suspicion that Ivan has somehow managed to clone himself, or perhaps we are seeing the outputs of an as-yet unnamed team of collaborators publishing in his name. Either way, things are crazy hot and changing on a daily basis, the “bleeding edge” of network automation indeed.

OSPF over unnumbered interfaces

This morning Ivan published a blog post about OSPF over unnumbered interfaces. The topology for that article can be found here; observant readers will quickly notice a problem with it, but we can easily fix that:

netlab up -d sros -p clab

That is, bring up the same topology, but use Nokia SR-OS devices and Containerlab instead of the defaults.

Topology with removed unnumbered multi-access link

As Ivan explains in his article, OSPF doesn’t work over unnumbered multi-access links, and so Netsim-Tools complains and stops you from wasting more time.

After the nodes boot (and adding support for OVS bridges), we get full adjacencies:

OSPF neighbors on R2

Adjacencies on all 3 interfaces of R2

Route table at R2; numbered interfaces are preferred due to the lower cost metric (5)

‘glue’ ARP entries for peers on unnumbered interfaces (local and remote MAC per port)

Unlike CSR, SROS does send out OSPF Hello packets on unnumbered multi-access interfaces, but it assumes they should be point-to-point interfaces instead. The adjacency fails to form because the interface type in the Hello packet (point-to-point) does not match the configured type — allowing the user to see an error in the logs.

Verbal feedback about why OSPF doesn’t come up

In summary

OSPF(v2) works just fine over unnumbered interfaces, now also on Nokia SROS using Netsim-Tools 1.1.

What would you like to see us do next?