BGP: Allow ipv6 LLA to numbered IPv6 peer (dynamic neighbors)

[jbemmel]

netlab/netsim/modules/bgp.py

Line 290 in 9ae2973

if ipv6_addr is True and not ipv6_lla:

and

netlab/netsim/modules/bgp.py

Line 307 in 9ae2973

if not features.bgp.ipv6_lla: # Finally, check the IPv6_LLA feature flag

currently block a topology as discussed in https://blog.ipspace.net/2025/04/worth-reading-bgp-unnumbered-2025/

Netlab insists that both sides have to be either numbered or unnumbered. However, dynamic neighbors features enable mixed peering scenarios too

Could these conditions be relaxed, or turned into quirks/warnings that can be selectively turned off?

[ipspace]

I know you were intrigued by that blog post that used Bird with Nokia/Juniper, but this is such a niche corner case that whoever wants to do it is more than welcome to write a plugin or whatever.

[jbemmel]

I agree it’s a niche use case, but how could a plugin disable the error?

Making it possible to disable the error keeps the default behavior, while allowing adventurous users to do their own thing

[ipspace]

I agree it’s a niche use case, but how could a plugin disable the error?

It cannot. It would have to work around it.

A) After the links are transformed, identify problematic interfaces
B) Set a flag to remember you changed something, then change the IPv6 address to LLA (for example)
C) In the "cleanup" hook, fix things.

Making it possible to disable the error keeps the default behavior, while allowing adventurous users to do their own thing

I see exactly one adventurous user who wants to have this changed 🤷‍♂️