This option supports devices conforming to the Communication Device
Class (CDC) Ethernet Control Model, a specification that's easy to
implement in device firmware. The CDC specifications are available
from <http://www.usb.org/>.

CDC Ethernet is an implementation option for DOCSIS cable modems
that support USB connectivity, used for non-Microsoft USB hosts.
The Linux-USB CDC Ethernet Gadget driver is an open implementation.
This driver should work with at least the following devices:

* Dell Wireless 5530 HSPA
* Ericsson PipeRider (all variants)
* Ericsson Mobile Broadband Module (all variants)
* Motorola (DM100 and SB4100)
* Broadcom Cable Modem (reference design)
* Toshiba (PCX1100U and F3507g/F3607gw)
* ...

This driver creates an interface named "ethX", where X depends on
what other networking devices you have in use. However, if the
IEEE 802 "local assignment" bit is set in the address, a "usbX"
name is used instead.

source code:

drivers/net/usb/cdc_ether.c