IPv6 Netowrk Device Numbering BP

Thu Nov 1 14:51:49 UTC 2012

On 2012-11-01, at 10:27, Sander Steffann <sander at steffann.nl> wrote:

>> You really shouldn't need to parse these and it's perfectly valid to reject them as invalid input. This really is an output only format [...]
> 
> I don't agree. I think it's actually the other way around. It's a valid representation of an IPv6 address so you be able to parse them. You don't need to be able to output them though.

The active advice from the IETF on this topic would seem to be RFC 5952 as updated by RFC 5952.

RFC 5952 specifies (in section 5) that the least-significant 32 bits MAY be written in dotted-quad notation if "it is known by some external method that a given prefix is used to embed IPv4". People who make use of a general-purpose v6 addressing plans which incorporate mapped v4 addresses in the lower 32 bits fit clearly into this category, I would think. 5952 is silent on the distinction between parsing such addresses and using them in output.

I don't see any justification in the standards for rejecting v4-mapped addresses on input. For what that's worth.

I agree that this adds a step to input validation, and that using standard libraries for this stuff is a good idea.

Joe