Allow duplicate DNS records if IPs have the anycast role

[fcavro]

Is your feature request related to a problem? Please describe.

When unique DNS records are enforced, it is not possible to assign the same DNS name to multiple anycast IP addresses within the same VRF.

I use multiple instances of the same anycast IP address, each assigned to an interface on a different device or VM. I would still like to use a managed DNS record for the shared IP address.

Currently, assigning the same DNS name to multiple anycast IP addresses results in a uniqueness validation error, even though all IP addresses represent the same logical anycast endpoint and should result in only a single A/AAAA record.

Describe the solution you'd like

The uniqueness check for managed DNS records should take the role of the current IP address and any existing matching IP addresses into account.

Multiple IP addresses with the Anycast role, the same address, and the same DNS name should be allowed and should result in a single managed A/AAAA record.

Describe alternatives you've considered

One possible workaround is to set the DNS name on only one of the anycast IP addresses.

Another option is to use the ipaddress_dns_disabled custom field on all but one of the IP addresses.

However, both approaches make the managed DNS record dependent on a specific IP object. Removing or disabling that IP would cause the managed DNS record to disappear.

Additional context

NetBox itself allows duplicate IP addresses for several special roles: Anycast, VIP, VRRP, HSRP, GLBP and CARP (https://github.com/netbox-community/netbox/blob/main/netbox/ipam/constants.py#L39).

Maybe it makes sense to apply the same uniqueness behavior to managed DNS records for these roles as well.

[peteeckel]

HI @fcavro, have you considered setting the enforce_unique_records setting in NetBox DNS to False? This would at least avoid the uniqueness validation failure.

Setting this option allow you to define multiple occurrences of the same record, which is usually not what you want - but might help you in your specific case.

What you really need would be one record for any set of anycast addresses. Internally, that record would need to map back to the whole set of IPAddress objects. This is a major change in the data model and (worse!) in the logic required to clean up the DNS records if anything changes ... what, for instance, should happen if one of the addresses stops being a anycast address? The logic behind that is not trivial at all.

Let me think about a way to implement this, but currently please don't hold your breath as I'm really busy with some other projects and won't even have time to explore this more deeply until well into next year.