Re: [v6ops] RFC7084

Ole Troan <> Tue, 10 December 2013 17:15 UTC

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Subject: Re: [v6ops] RFC7084
From: Ole Troan <>
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Date: Tue, 10 Dec 2013 18:14:56 +0100
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>> As far as I know the M flag is linked only to IA_NA. As far as I can see IA_PD is not linked to the M flag at all.
> There is no agreement on what the M and O bits do.   Some people think M means stateful address management; some think M means IA_NA and O means IA_PD.   RFC 4861 is actually fairly clear, at least to my reading of it, that "M" means IA_NA and IA_PD, and that "O" means stateless DHCPv6, but I've heard people argue vehemently that "M" means _only_ IA_NA, and that "O" means IA_PD, because prefixes aren't addresses.

that's incorrect. there are no flags in the RA that indicates if prefix delegation is available or not.
prefix delegation is between routers, routers don't listen to RAs was the rationale.

> So if you believe my reading of RFC 4861, you would set 'M' and expect the HG to get both IA_NA and IA_PD; RFC 7084 makes it clear that _either_ the 'M' or 'O' bit being set triggers the HG to do prefix delegation.

a RFC6204 CPE must act as a requesting router and request IA_PD in all cases.
it may choose to request the IA_NA based on the M flag or it might do so regardless, both
approaches are fine.

> So if you want to do prefix delegation and not stateful address assignment, set the 'O' bit and _not_ the 'M' bit, even though that contradicts what RFC 4861 says.

no, that's not what these flags mean.