about MC7455 RAW IP mode

[Dan Williams]

On Wed, 2017-02-22 at 20:00 +0000, Chen, Jing wrote:
> Hi, All:
> 
> My RWAIP MC7455 has been allocated an IP address from wireless
> network and this IP address is registered in Linux host (ipconfig and
> DHCP are succeeded). While it has some issue on sending/receiving
> data packets.  I found the following info
> 
> ************
> This patch adds support for "raw IP" framing for QMI devices,
> changing the netdev from an ethernet device to an ARPHRD_NONE
> p-t-p device when "raw IP" framing is enabled.
> ************
> 
> Is it meaning that data packets shall be send to MC7455 with IP
> header + no MAC address , and there is no ARP needed? Which type of
> socket shall be generated to RAW IP interface, i.e. socket(PF_INET,
> SOCK_RAW, htons(IPPROTO_RAW))?

This is 100% hidden from applications that use IP.  RawIP and 802.3 is
mostly between the qmi_wwan kernel driver and the device itself.  As
long as the driver and device agree on whether they are using raw-ip or
8023, things will work for applications.

You are correct, no ARP is required when in raw-ip mode, but the kernel
driver handles this for you by setting IFF_NOARP on the net device.

Unless your application actually tries to send ethernet packets to the
device (which would be odd, since no WWAN devices actually speak
ethernet, and those that appear to speak ethernet just fake it) you
don't have to change anything to use raw-ip mode.

Your application simply opens normal IP-type sockets
(PF_INET+SOCK_DGRAM, PF_INET+SOCK_STREAM, or PF_INET+SOCK_RAW) and
sends/receives normal IP packets, and the kernel handles moving the
packets to and from the WWAN network interface as directed by its
routing tables.

Dan

> Thanks!
> 
> 
> Jenny
> 
> 
> 
> 
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