dhcpcd: raw-ip support

[Bjørn Mork]

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

> Is there any raw-ip related documentation?

Not really. Just delete "ethernet" from other documentation :-)

The only difference is that the ethernet header is removed from the
packets between host and modem.  It is not replaced by anything.

We could have made up a new "ARP hardware type" for this, but I didn't
see much point.  The "hardware type" is simply no header and no
address. So I went with the example from the tuntap driver, using
ARPHRD_NONE



Bjørn