Has anyone done DHCPv6-PD over a mobile link?

Bjørn Mork bjorn at mork.no
Sun Jan 17 20:55:11 UTC 2021

How did you do that?  Is there any best practice?

Say I have a dual stack PDN link up and running using a USB connected
modem.  But I am going to use this in a CPE and need more addresses than
that single /64.

So I want to send a DHCPv6 solicit over the mobile link requesting an
IA_PD.  But a USB "modem" is actually a router with a mobile interface
and a USB interface.  So I can't just fire up a DHCPv6 client on the USB
host.  It will send the solicit to the modem using a link local source
address and the ff02::1:2 link scoped multicast address as
destination. This solicit obviously stops at the modem, unless the
firmware is prepared to do anything with it.  Which I don't think mine
will (are there such firmwares?).  Anyway, I don't want to depend on a
firmware solution.  They tend to be buggy, and will also lock the
solution to a specific modem and firmware version.  Which I don't want.

So I tried using a relay agent on the host behind the modem, wrapping
the solicit in a DHCPv6 relay request with a global source address from
the PDN assigned /64 and the ff05::1:3 site scoped multicast address as
destination.  This works, sort of.  The relay packet arrives at the PGW,
and we just need to figure out how to get the PGW or some other DHCPv6
server to answer it and update routing accordingly.

But I wonder if this is the proper way to do things?  I am worried about
not being able to find a single example of something similar. Searching
for DHCPv6-PD in a mobile context just results in pointer on how to
replace the local pool on the PGW with a DHCPv6 server.  This is not
what I want to do...

So does anyone know of a network supporting DHCPv6-PD?  Doesn't really
matter if you are user or operator or vendor or whatever.  I'd just like
to verify that we're not inventing a square wheel.


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