dhcpcd: raw-ip support

Yegor Yefremov yegorslists at googlemail.com
Mon Aug 19 14:20:49 UTC 2019

On Mon, Aug 19, 2019 at 2:57 PM Bjørn Mork <bjorn at mork.no> wrote:
> 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.

How one supposed to set the IP configuration via QMI? I can connect using:

qmicli --device=/dev/cdc-wdm0 --device-open-proxy

and get IP config via:

# qmicli -d /dev/cdc-wdm0 --device-open-proxy
--wds-get-current-settings --client-cid=17
[/dev/cdc-wdm0] Current settings retrieved:
           IP Family: IPv4
        IPv4 address:
    IPv4 subnet mask:
IPv4 gateway address:
    IPv4 primary DNS:
  IPv4 secondary DNS:
                 MTU: 1430
             Domains: none

How can these settings be automatically applied to wwan0? Am I missing
related MM options here?


> 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

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