[186227] in North American Network Operators' Group
Re: DHCPv6 PD & Routing Questions
daemon@ATHENA.MIT.EDU (Owen DeLong)
Sat Dec 5 19:08:01 2015
X-Original-To: nanog@nanog.org
From: Owen DeLong <owen@delong.com>
In-Reply-To: <20151125235950.6E5293D93209@rock.dv.isc.org>
Date: Sat, 5 Dec 2015 16:05:44 -0800
To: Mark Andrews <marka@isc.org>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
> On Nov 25, 2015, at 15:59 , Mark Andrews <marka@isc.org> wrote:
>=20
>=20
> In message =
<CAMWxDfrh+O=3DSPZwPmAZhYnvAEeK2eMFw3CD0qf34Fkbb=3D-SaPw@mail.gmail.com>, =
Brian Knight writes:
>> On Tue, Nov 24, 2015 at 6:34 PM, Baldur Norddahl
>> <baldur.norddahl@gmail.com> wrote:
>>>=20
>>> 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 (*).
>>>=20
>>> 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.
>>=20
>> 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.)
>>=20
>> 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.
>>=20
>> -Brian
>=20
> Well the requesting router could announce the route. ISC's client
> has hooks that allow this to be done. That is, after all, how
> routing is designed to work. The DHCP server usually is sitting
> in a data center on the other side of the country with zero ability
> to inject approptiate routes.
>=20
Are you really suggesting that a residential ISP accept routes =
advertised
from their customer=E2=80=99s CPE? Really?
That=E2=80=99s about the most ridiculous thing I=E2=80=99ve heard on =
NANOG in a long time
and that=E2=80=99s saying something.
> The DHCP relay could also have injected routes but that is a second
> class solution.
Maybe, but in an ISP/Customer PD environment, it=E2=80=99s certainly =
preferable
to what you consider a =E2=80=9Cfirst class=E2=80=9D solution.
Owen
