[networkd] Ability to selectively ignore IPv6 prefixes supplied via router advertisement

[chrsmrtnx]

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

On networks where multiple prefixes are supplied via router advertisements, it can be difficult to keep control of the addresses assigned to your hosts. For instance, when I manually assign a ULA to a host, but on the network that prefix is also advertised via RA (for the benefit of Android devices, let's say), then my host will wind up with: (1) the assigned ULA; (2) an address formed from the ULA prefix plus the EUI-64 interface ID; and (3) a privacy address formed from the ULA prefix - when the only one I actually want is the manually assigned ULA. Aside from being a mess, this creates problems in situations where the exact source address matters. And yes, I need to accept RAs in order to obtain the global prefixes that change periodically from my provider.

Describe the solution you'd like

An option to ignore specific prefixes from RAs, or classes of prefixes (such as 'global' or 'ULA') would allow more precise control over IPv6 networking in general. A further option could accept the prefix/prefix class in question, but not generate privacy addresses.

[kpfleming]

What you're asking for is to disable SLAAC, not to ignore prefixes received in RAs. This is already being discussed in other issues, including #969.

[chrsmrtnx]

Not exactly the same as #969. What I requested was a more fine-grained ability to control which prefixes (obtained via RA) are actually processed and used. I don't want to disable SLAAC entirely.

[kpfleming]

Fair point; unfortunately SLAAC is processed in the kernel, not in systemd, and the kernel doesn't offer this type of control at this point.

[yuwata]

Does #11716 help this issue/RFE? @ssahani What do you think about?

[ssahani]

This issue about selecting one or more prefixes from multiple prefixes . So It does not look like that fixes it.

[yuwata]

Please test #12603 if possible. Thank you.