ifindex attribute at link level

[jbemmel]

Small feature - I'd like to declare a single ifindex attribute for a link, and have it applied to all (usually 2) interfaces on that link.
For consistency when deploying pairs of devices, it's usually easiest if the same ports are used on both sides

I can create a PR if no objections

[ipspace]

That would only work for containers where containerlab names the interfaces anything it wishes when creating them in the container namespace. There's no such direct connection between libvirt interfaces and VM interfaces.

Also, don't we already have ifindex on interface-on-a-link level? What's wrong with that?

Finally, the current code does not check for overlapping values, so you might get some interesting problems.

In my opinion, including this in netlab core is too much hassle for too little impact (plus giving people too much rope to hang themselves).

[jbemmel]

This is just to populate ifindex consistently on both ends of a p2p link for example:

links:
- r1:
  r2:
  ifindex: 49 # To select 100G port 1/1/49 on both sides - assumes both are the same type of device

instead of

links:
- r1:
    ifindex: 49
  r2:
    ifindex: 49

The semantics are to copy the link attribute to the interfaces, unless the interface already has a value

[ipspace]

Not a problem. Change ifindex to be link attribute, make sure it's still recognized as an interface attribute, and that you can apply it at both places (best would be to create a new test case) and submit a PR ;)

I looked at the code and it should work with minimal changes, unless you want to do the RIGHT thing and make sure ifindex values don't overlap (IIRC at the moment we just take the number of interfaces and increase it by one)