CDCE(4) FreeBSD Kernel Interfaces Manual CDCE(4)


cdceUSB Communication Device Class Ethernet driver


To compile this driver into the kernel, place the following lines in your kernel configuration file:

device uhci
device ohci
device usb
device cdce

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):



The cdce driver provides support for USB Host-to-Host (aka USB-to-USB) and USB-to-Ethernet bridges based on the USB Communication Device Class (CDC) and Ethernet subclass.

The USB bridge appears as a regular network interface on both sides, transporting Ethernet frames.

For more information on configuring this device, see ifconfig(8).

USB 1.x bridges support speeds of up to 12Mbps, and USB 2.0 speeds of up to 480Mbps.

Packets are received and transmitted over separate USB bulk transfer endpoints.

The cdce driver does not support different media types or options.


The following devices are supported by the cdce driver:

  • Prolific PL-2501 Host-to-Host Bridge Controller
  • Sharp Zaurus PDA
  • Terayon TJ-715 DOCSIS Cable Modem


cdce%d: no union descriptor
The driver could not fetch an interface descriptor from the USB device. For a manually added USB vendor/product, the CDCE_NO_UNION flag can be tried to work around the missing descriptor.
cdce%d: no data interface
cdce%d: could not read endpoint descriptor
cdce%d: unexpected endpoint
cdce%d: could not find data bulk in/out
For a manually added USB vendor/product, these errors indicate that the bridge is not compatible with the driver.
cdce%d: watchdog timeout
A packet was queued for transmission and a transmit command was issued, however the device failed to acknowledge the transmission before a timeout expired.
cdce%d: no memory for rx list -- packet dropped!
Memory allocation through MGETHDR or MCLGET failed, the system is running low on mbufs.
cdce%d: abort/close rx/tx pipe failed
cdce%d: rx/tx list init failed
cdce%d: open rx/tx pipe failed
cdce%d: usb error on rx/tx


arp(4), intro(4), netintro(4), usb(4), ifconfig(8)

Universal Serial Bus Class Definitions for Communication Devices, http://www.usb.org/developers/devclass_docs/usbcdc11.pdf.

Data sheet Prolific PL-2501 Host-to-Host Bridge/Network Controller, http://tech.prolific.com.tw/visitor/fcabdl.asp?fid=20679530.


The cdce device driver first appeared in OpenBSD 3.6, NetBSD 3.0 and FreeBSD 6.0.


The cdce driver was written by Craig Boston <craig@tobuj.gank.org> based on the aue(4) driver written by Bill Paul <wpaul@windriver.com> and ported to OpenBSD by Daniel Hartmeier <dhartmei@openbsd.org>.


Many USB devices notoriously fail to report their class and interfaces correctly. Undetected products might work flawlessly when their vendor and product IDs are added to the driver manually.
September 17, 2005 FreeBSD