Re: RFC7084

Ole Troan <otroan@employees.org> Mon, 09 December 2013 22:02 UTC

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Subject: Re: RFC7084
From: Ole Troan <otroan@employees.org>
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Date: Mon, 09 Dec 2013 23:02:03 +0100
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To: Sander Steffann <sander@steffann.nl>
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>> Not sure I should sent this one to DHCPv6 WG or the global IETF v6, so feel free to forward it if needed.

this is a product of the v6ops working group, so probably the discussion belongs there.

>> Last week, RFC7084 got posted.  I did already post a message on a rather badly phrased req (a SHOULD one regarding “long-enough”, but bumped into the next one today (this one being a lot worse!!).
>> 
>> “”
>> WAA-6:   If the IPv6 CE router receives a Router Advertisement
>>            message (described in [RFC4861]) with the M flag set to 1,
>>            the IPv6 CE router MUST do DHCPv6 address assignment
>>            (request an IA_NA option).
>> “”
>> I’m not sure who came up with this one, but this is really a no-go.
>> So, according to this req, the DHCPv6 client must request an ia_na option if an M=1 is being received on his link ???  I might have understood it all wrong, but as far as I know, M=1 is not linked directly to ia_na, ia_pd is enough on its own, no ??
> 
> Actually the other way around: M=1 is linked to ia_na but not to ia_pd. A CPE always does ia_pd, regardless of the M flag, but the ia_na is only requested when M=1.

the text is written so that there does not have to be any binding between RA processing and the DHCP state machine.
a CPE can simply ignore the O/M flags, and always request an IA_NA.

>> So, the CPE is expected to change its DHCPv6 client configuration based upon receiving an RA with this M=1 content ?
> 
> Yep, that's the meaning :-)

or it can ignore it, see above.

>> I’m very curious on the replies now, but this seems really be going the wrong way.  You can launch a CPE which either listen to RA or not, and bound accordingly, however, listen + bind + force ia_na looks a bit too much to me.
> 
> You always have to listen to RA, otherwise you won't have your default gateway. If you don't want a global address on the CPE WAN link (assuming that A=0 in the prefix option, but it doesn't have to be) you could ignore the M=1 flag and not do ia_na.

cheers,
Ole