Why used DHCPv6 when RA has RDNSS and DNSSL?

[Fernando Gont]

Hi, Brian,

On 31/3/20 00:29, Brian E Carpenter wrote:
> It seems that the router must be setting both the A bit (use SLAAC) and the M bit (use DHCPv6). 

FWIW, my  Sagemcom router provided by my ISP does the same (set both A 
in PIOs, and M (and O :-) ) in the RA). UBuntu reacts as descirbed by 
the OP.


> So the host is obeying both. There's no real harm in it, in most circumstances.

Not sure I would clasify it as "harm", but:
my ubuntu box does rfc7217+rfc4941. But since the M bit is set, it 
configures a DHCPv6-leased address... with a predictable IID. ( 
apparently the CPE has a poool that starts at ::1000, and leases 
addresses incrementally).

Certainly, that's not nice.

Besides, if folks are concerned about the number of addresses in use (as 
some did in recent 6man discussions), one would say this is a 
low-hanging fruit: an address that is configured, and will *never* be used.



> Fixing the ambiguity about what hosts should do about this has often been discussed in the IETF but there's never really been evidence that it's worth doing.

FWIW, me, even if it was just for the sake "clarity", that would be 
worth doing.

Thanks!

Cheers,
-- 
Fernando Gont
e-mail: fernando at gont.com.ar || fgont at si6networks.com
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