Built-in device interfaces versus NSO created interfaces

[ryan-hitch]

I am seeing a difference between the way NSO is treating device interface configurations and just want to make sure this is intential.

For example, a user adds the following command to Cisco router interfaces GigabitEthernet0/0 and BDI10 using the router CLI.

ip tcp adjust-mss 1400

Both interfaces have other parameters which were configured with an NSO service (ip address, no ip proxy-arp, etc). BDI10 is a virtual interface that was created by the service, however GigabitEthernet0/0 was not since it is a "built-in" physical interface on the device.

When a user makes a service modification with NSO, NSO wants to remove ip tcp adjust-mss 1400 from BDI10, but not GigabitEthernet0/0.

I assume this has something to do with NSO having created BDI10 and all parameters under that interface (container?) are then considered managed by NSO? The service model is being updated to account for additional configuration parameters such as this, but I was surprised to see the difference in behavior and would like to understand the undelying functional difference.

[yfherzog]

Hi,

This is probably not happening due to the fact that NSO created one of the interfaces and not the other, but due to differences in reference counters on the specific command (ip tcp...) on each of the interfaces.

If the command existed on the interface before the service was deployed, or if there's another service that consumes the command (e.g. have it in its XML templates), then when the service instance is removed, the refcount will remain larger than zero, and it will not be removed from the device.

If NSO service(s) created the command in the first place, then once all service instances to do that are removed, refcount should be zero, and the command should be removed.