using ULA for 'hidden' v6 devices?

Owen DeLong owen at
Thu Jan 26 13:48:47 UTC 2012

On Jan 26, 2012, at 2:00 AM, George Bonser wrote:

>> Use different GUA ranges for internal and external. It's easy enough to
>> get an additional prefix.
>>> As others have mentioned, things like management interfaces on access
>> switches, printers, and IP phones would be good candidates to hide with
>> ULA.
>> Or non-advertised, filtered GUA. Works just as well either way.
>> Owen
> If one is obtaining "another" prefix for local addressing, I see no benefit.  I am assuming that anyone that is using ULA is using it for things that don't communicate off the site such as management interfaces of things, etc.  This won't be a subnet you are connecting by VPN to another organization, usually, but even if you do the chances of collision is pretty low if you select your nets properly.  But for the most absolutely paranoid site, I can see some appeal in using ULA in conjunction with DNS64/NAT64 and see them giving the devices internet access via v4.  Not that I agree with the notion, mind you, just that I can see someone looking at that as an appealing solution for some things.  Even if someone managed to get through the NAT device via v4, they would have nothing to talk to on the other side as the other side is all v6.

Even if you don't see an advantage to GUA, can you point to a disadvantage?

IMHO, it would be far less wasteful of addressing overall to deprecate fc00::/7 and use unique secondary GUA prefixes for this purpose than to use ULA.

If you can't point to some specific advantage of ULA over secondary non-routed GUA prefixes, then, ULA doesn't have a reason to live.

I'm not sure where DNS64/NAT64 comes into play here for v6 to v6 communication. For IPv4, I don't see any advantage in ULA+NAT64 vs. the more reliable and easier RFC-1918 with NAT44 possibilities, even if you have to run multiple RFC-1918 domains to get enough addresses, that will generally be less complicated and break fewer things than a NAT64 implementation.


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