Re: [dhcwg] two comments on draft-cui-dhc-dhcpv6-prefix-length-hint-issue

Actually for IA_PD you would get NoPrefixAvail (and that is in the Status Code option encapsulated in the IA_PD).

I think there may be servers that do not support (implement) IA_PD at all, which would result in no IA_PD in the Advertise (or Reply).

So a client should handle both cases.

---

Also, the best way to assure a completely new delegated prefix (or an address), is to send a new IAID in the IA_PD. This assures the device would get a new delegated prefix. The client can release the old one or just let it gracefully expire.

There are some negative consequences with this changing the IAID of the IA_PD if the device has no persistent storage since rebooting the device would cause it to use the original IAID on the IA_PD and then it would either get another prefix or the original one back (if the original hadn't been released or expired, ignoring any kind of grace time issues that a server might use).

- Bernie

-----Original Message-----
From: dhcwg [mailto:dhcwg-bounces@ietf.org] On Behalf Of Dan Seibel
Sent: Thursday, July 23, 2015 8:55 AM
To: Alexandru Petrescu
Cc: dhcwg@ietf.org
Subject: Re: [dhcwg] two comments on draft-cui-dhc-dhcpv6-prefix-length-hint-issue

For #1 I would think sending a solicit with IA_PD is how you can find out if the server supports it.  If it does you will get a prefix returned, if not you will get a Noaddrsavail for the IA.

> On Jul 23, 2015, at 6:38 AM, Alexandru Petrescu <alexandru.petrescu@gmail.com> wrote:
> 
> Hello,
> 
> I just read draft-cui-dhc-dhcpv6-prefix-length-hint-issue-00.
> 
> I am happy this draft exists and I have two comments.  One is more 
> general question in this context, and the other a potential 
> improvement, but not a request.
> 
> The draft assumes the Client is a Host which may request a prefix len 
> at some point, and another one maybe later.  It seems the prefix is to 
> be used on the interface which has issued that Solicit.  And it seems 
> to face a Server sure to be willing to deliver a prefix.
> 
> 1. What is the best way to query a DHCPv6 Server to ask it whether or 
> not it supports Prefix Delegation at all?
> 
> 2. when this Router changes mind and requests a different prefix, 
> maybe with a different length, a specification like 
> draft-cui-dhc-dhcpv6-prefix-length-hint-issue could recommend to 
> deprecate that prefix with specific consideration to below it, not 
> just to the Server.
> 
> I mean this something like this:
> 
> Current text:
>> 1.Deprecate the old prefix right away by sending a Release message to 
>> the server, and switch over to the new prefix.
> 
> New text:
>> 1.Deprecate the old prefix right away by sending a Release message to 
>> the server, and switch over to the new prefix.  And by stopping 
>> sending RAs on its other interfaces with the old prefix, stop 
>> propagating it in the routing protocol.
> 
> Alex
> 
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