DHCPv6-PD in mobile networks

[Bjørn Mork]

Still struggling with this.  Would appreciate any hints.  Anyone tried
IPv6 on a mobile connection with a shorter prefix than /64?  How do you
do that?

Assuming DHCPv6-PD, one basic problem is the selection of source and
destination addresses for the solicit.  I really don't understand how
this is intended to work given any real world USB/PCIe 4G/5G modem,
which basically always is a closed firmware router with one USB/PCIe
interface and one radio interface.

Are we supposed to have special device specific firmware support, so
that we can use a magic firmware command to send solicits from a link
local address to the link local ff02::1:2 multicast group over the
mobile link?  If so, any tips regarding actual implementations?

Ruling out special modem firmware, am I right assuming that using
ff05::1:3 with a GUA source from the dual-stack PDP context assigned /64
should work?  And if it does, would it be OK if the solicit is wrapped
in a DHCPv6 relay message?  That's the most generic solution I can come
up with. But maybe it's just my lack of imagination...

Google finds a number of documents with lots of hand-waiving and no
specifics wrt the IP addresses involved or the actual DHCPv6 packet
contents.  Making it look like the UE can just send a DHCPv6-PD solicit
like it was an ordinary ethernet client.  But I don't know of any modem
where we have that kind of access to the actual tunnel.  Unless we go
back to PPP. I kind of don't think that's the intention....

Some documents indicate that the Prefix Exclude option (RFC6603) might
be required, but I don't have any more success if I request this option.

FWIW, I am of course able to send a DHCPv6 solicit to arbitrary DHCPv6
servers, using a GUA destination. So assuming I can configure the client
side realys, then this is a possible solution.  The problem is that I
need the PGW to pick up the routing somehow.  I can think of a number of
creative ways to do that.  But I'd rather not be too creative.  Doing
what everyone else does is preferred.  But what is that?


Bjørn