Re: using ULA for 'hidden' v6 devices?

[Tim Chown <tjc () ecs soton ac uk>]

So the issue of ULAs has come up in the IETF homenet WG.  The homenet WG is considering routing, prefix delegation, 
security, naming and service discovery. 

ULA support is written into RFC6204 (basic IPv6 requirements for CPE routers) so home CPEs should have the capability, 
and should be able to generate "random" ULA prefixes.

The potential advantage of ULAs is that you have a stable internal addressing scheme within the homenet, while your 
ISP-assigned prefix may change over time.  You run ULAs alongside your PA prefix.  ULAs are not used for host-based 
NAT.  The implication is that all homenet devices carry a ULA, though whether some do not also have a global PA address 
is open for debate.

There's a suggestion that ULAs could be used to assist security to some extent, allowing ULA to ULA communications as 
they are known to be within the homenet.

The naming and service discovery elements should remove the need to ever manually enter a ULA prefix; thus the 
temptation to use 0 instead of random bits for the ULA prefix should be reduced (even if the CPE allows it).

Prefix delegation of ULAs within a homenet would be done the same way as for the global PA prefix.

There is a proposal (not from within the homenet WG) to use ULAs with NPT66 (RFC6296).  That obviously has some 
architectural implications.

Tim