Android (lack of) support for DHCPv6

Wed Jun 10 15:45:48 UTC 2015

On 10 June 2015 at 15:53, Mikael Abrahamsson <swmike at swm.pp.se> wrote:

>
> Well, then you're not doing what most people do when they do DHCPv6-PD,
> you're using something else. This is the first time I have heard of anyone
> doing what you describe.
>

I mentioned because the Android guy seems to be guilty of knowing how
everyone does or want to run their network. There are always more ways to
do this than you thought of.

Normally it's done by the router acting on DHCPv6 packets and installing a
> route if need be.
>

I would probably do it like that if my equipment had support. But it does
not. And I can not point at any RFCs to tell my vendor that their stuff is
broken, because the requirement simply is not in any RFCs.

Also consider this:

1) The DHCP relay might not be the same router that needs to do the
forwarding.
2) There might be more than one router that can forward.
3) There might not even be a DHCP relay, the DHCP server could be attached
directly.

In our case we have GPON access switches that do DHCP(v6) snooping. These
things can block illegal traffic, but other than that, they are purely
layer 2 devices. There is no relay there and no layer 3 forwarding, so no
routes can be installed by anything.

Upstream from the access switches there are many ways you can structure
your network. You might want to have two routers for redundancy. You may
attach the DHCP server directly here if it is a small network (although we
use relays).

Static routes with a fixed GUA next hop for the /48 prefix delegations
means you can have some pretty dumb (=cheap) stuff in your network. All you
need is an intelligent DHCP server and that is just open source software on
a Linux.

I considered having the DHCP server add the routes via a script that is
triggered by lease handout. But the fixed static routes is much simpler and
robust.

> I do agree that you do not want your equipment sitting in the same
> broadcast domain as all the customers devices, but do use PD. I'm just
> baffled by the way you have implemented "PD".
>
>
We all work with the equipment we got and the quirks in there. Just do not
go around and assume everyone has the same requirements as you. Saying
there is no use case for DHCPv6 except for PD is dumb and that was why I
put forward a use case to illustrate how this is used in the real world. At
least by us.

Regards,

Baldur