dhcpcd: raw-ip support

[Bjørn Mork]

Yegor Yefremov <yegorslists at googlemail.com> writes:
> On Mon, Aug 19, 2019 at 10:49 AM Bjørn Mork <bjorn at mork.no> wrote:
>> Yegor Yefremov <yegorslists at googlemail.com> writes:
>>
>> > I have a project where I'm using dhcpcd client. It is working without
>> > any problems with older modems like Quectel UC20 etc. But now we want
>> > to switch to SIM7600G-H and it is working in raw-ip mode. So far only
>> > udhcpc can handle such MAC address-less interfaces.
>> >
>> > Do you know what is so special about udhcpc compared to other DHCP
>> > clients?
>>
>> It's mostly L2 agnostic, meaning that it will work on non-ethernet
>> interfaces.
>>
>> "Fixing" this for other clients isn't really that hard, if required. I
>> did this proof-of-concept for ISC dhclient for example:
>>
>>  https://mail.gnome.org/archives/networkmanager-list/2015-December/msg00044.html
>
> Thanks for the patch. But looks like it hasn't been upstreamed yet :-(

Upstreaming anything to ISC is not possible in my experience.  See
https://lists.isc.org/pipermail/dhcp-users/2011-August/013926.html

Or at least not worth the extra effort required.

And I don't think raw-ip support is all that useful, to be honest.  The
DHCP server in the modem is a hack anyway.  You should use the modem
management channel to get IP config from the modem.  I.e. QMI.

But DHCPv6 support on PPP links is something else.  It's an essential
feature for a DHCPv6 client.  As you may or may not know, IPV6CP is very
different from IPCP when it comes to address negotiation. It will only
negotiate an interface-id and leave the remaining address config to the
normal autoconf protocols.  I.e. you need to run SLAAC and/or DHCPv6 on
the link if you want a global address.

Somewhat off-topic here. Unless you have a modem with support for IPv6
over PPP, which I recently learned actuall exists:
https://forum.openwrt.org/t/ipv6-with-ppp-with-3g-modem/39071

I'll stop babbling now


Bjørn