Re: [v6ops] I-D Action: draft-jjmb-v6ops-unique-ipv6-prefix-per-host-00.txt

["Templin, Fred L" <[e-mail]>]

Hi Brian,

> -----Original Message-----
> From: Brian E Carpenter [mailto:[e-mail]]
> Sent: Thursday, October 29, 2015 3:45 PM
> To: Templin, Fred L; [e-mail]
> Cc: Tore Anderson; [e-mail]; 神明達哉
> Subject: Re: [v6ops] I-D Action: draft-jjmb-v6ops-unique-ipv6-prefix-per-host-00.txt
> 
> Ole, Fred,
> 
> On 30/10/2015 11:03, Templin, Fred L wrote:
> > Hi Brian,
> >
> >> -----Original Message-----
> >> From: [e-mail] [mailto:[e-mail]]
> >> Sent: Thursday, October 29, 2015 2:59 PM
> >> To: Brian E Carpenter
> >> Cc: Templin, Fred L; Tore Anderson; [e-mail]; 神明達哉
> >> Subject: Re: [v6ops] I-D Action: draft-jjmb-v6ops-unique-ipv6-prefix-per-host-00.txt
> >>
> >> Brian,
> >>
> >>>> Hi, I won't disagree with Brian and Tore but on some IPv6 links waiting to
> >>>> receive an RA may be redundant and unnecessary before directly
> >>>> attempting DHCPv6 PD. On those links, DHCPv6 messaging alone may
> >>>> be all that is necessary, and no RS/RA is required.
> >>>
> >>> How is an IPv6 stack fresh from the factory supposed to guess that?
> >>> Surely we don't want to add configuration knobs?
> >>>
> >>> I think RA is a required feature. RFC 6434 says:
> >>>
> >>> 7.2.2.  Use of Router Advertisements in Managed Environments
> >>>
> >>>   Nodes using the Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
> >>>   are expected to determine their default router information and on-
> >>>   link prefix information from received Router Advertisements.
> >>> ...
> >>> 12.2.  Neighbor Discovery for IPv6 - RFC 4861
> >>>
> >>>   Sending Router Advertisements and processing Router Solicitations
> >>>   MUST be supported.
> >>
> >> in the general case:
> >> it isn't required for router to router links.
> 
> That may be so in practice, but is it actually documented that way?
> (I agree that it makes sense.)
> 
> >> nor is it required for DHCPv6 PD.
> 
> I don't see any wiggle room in the section 12.2 quote above. But anyway,
> the only practical interpretation of that is "if you think you might
> like to get an IA_PD, then try DHCPv6 regardless of RA."
> 
> >>
> >> in the 7084 case:
> >> we've tied the CE router's default routing to ND Router Discovery.
> 
> Right... which is a safe choice, because it's consistent with RFC 6434.
> 
> >
> > The same as what Ole said. Also, an IPv6-over-(foo) document can specify that
> > DHCPv6-only autoconfiguration is used on that link.
> 
> Really? RFC 4861 does allow exceptions, but mainly in terms of NBMA
> links.

Yes, I should have said NBMA. That is what I meant.

> Also, DHCPv6 is only a SHOULD in node requirements.

That is for IPv6 node requirements, yes. Requirements for nodes that
connect to a specific link type can change the SHOULD to a MUST.

> > In that way, IPv6 nodes
> > that connect to a (foo) link already known in advance what sorts of link
> > ND/DHCPv6 services they can expect.
> 
> Well, the IPv6-over-foo modules can know in advance. But host stacks as a whole
> need to figure this out dynamically, I think. Again, I am assuming that we want
> to get avoid configuration knobs.

A node connecting to a link type that has DHCPv6 as a MUST will naturally
do DHCPv6, yes.

Please note that I am not saying "DHCPv6-only". IPv6 ND functions such
as Redirect and NUD may still be needed, and if the node sends an RS
it should probably expect to receive an RA in reply (unicast).

Thanks - Fred
[e-mail]

> Regards
>    Brian