[186084] in North American Network Operators' Group
Re: DHCPv6 PD & Routing Questions
daemon@ATHENA.MIT.EDU (Brian Knight)
Wed Nov 25 18:37:46 2015
X-Original-To: nanog@nanog.org
In-Reply-To: <CAPkb-7D3J8yCdvPkZvwgrWTmxbcunEi7xhGrcnCtAervc5cBYA@mail.gmail.com>
Date: Wed, 25 Nov 2015 15:30:12 -0600
From: Brian Knight <ml@knight-networks.com>
To: Baldur Norddahl <baldur.norddahl@gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
On Tue, Nov 24, 2015 at 6:34 PM, Baldur Norddahl
<baldur.norddahl@gmail.com> wrote:
>
> DHCPv6-PD allows multiple PD requests. But did anyone actually implement
> that? I am not aware of any device that will hand out sub delegations on
> one interface, notice that it is out of address space and then go request
> more space from the upstream router (*).
>
> DHCPv6-PD allows size hints, but it is often ignored. Also there is no
> guidance for what prefix sizes you should ask for. Many CPEs will ask for
> /48. If you got a /48 you will give out that /48 and then not honor any
> further requests, because only one /48 per site is allowed. If you are an
> ISP that gives out /48 and your customers CPE asks for a /56 you will still
> ignore his size hint and give him /48.
Or, worse, the ISP's DHCPv6 server honors the new request and issues
the larger prefix, but refuses to route it. Ran into that myself when
I replaced my home CPE router, and changed the prefix hint to ask for
a /60 block (expanded from /64) at the same time. That made for a
frustrating few days without IPv6 service, waiting for my original
delegation to expire. (Tech support, of course, had no clue and
blamed my router.)
In retrospect I should have perhaps had my original CPE generate a
DHCP release message for that prefix before disconnecting it. But I
won't be the last person to fail to generate that.
-Brian
