RADVD RDNSS entry is not checked for "suffix only" with unexpected behavior

[meyergru]

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Describe the bug

In the RDNSSD entry for RADVD, you can enter e.g. "::88:99".

While I would expect that suffix to be prepended with the current /64 interface prefix to indicate some name server on the same interface (much like what happens when you enter nothing), the entry is copyied verbatim to /var/etc/radvd.conf.

To Reproduce

Steps to reproduce the behavior:

1. Go to RADVD settings
2. Click on advanced settings
3. Enter "::88:99" into the RDNSS server field and apply.
4. Look into generated section in /var/etc/radvd.conf

Expected behavior

Either the /64 prefix should be prepended for such suffixes or there should be a validation keeping you from entering suffixes only.

Describe alternatives you considered

None.

Additional context

See: https://forum.opnsense.org/index.php?msg=262685

Environment

Software version used and hardware type if relevant, e.g.:

OPNsense 26.1.4 (amd64).

[AdSchellevis]

The help doesn't mention any special expansion, in which case default IPv6 rules apply, this also means ::88:99 is just a valid address, just not the one you might want to use (a lot of zeros ending with 88:99).

[fichtner]

I don't remember that this was ever supported. I'd leave to leave it this way, too.

[meyergru]

Correct, it never was supported - it was only my expectation, because dynamic firewall aliases act the same way and the default would be to use the interface address even if left blank.

It would be nice to have it when you want another DNS server like AdguardHome on your network and you only have dynamic prefixes from your provider. Thus, it is more a feature than a bug.

Is an IPv6 address with all zeros in the first 64 bits really valid?

[AdSchellevis]

Is an IPv6 address with all zeros in the first 64 bits really valid?

yep, just try any of the online validators and they will likely all report the same.