Ethernet configuration testing protocol (CTP)


CTP is a part of the original Ethernet specification that doesn't appear in IEEE 802.*, or any other specification I can find on-line. It's basically a layer two "ping" equivalent. It would be useful if more people and operating systems implemented it.

My involvement

When I worked at BBN Planet in the late 1990's, I somehow became aware that there was something called the "Ethernet loopback protocol", which has ethertype 0x9000. I had a great deal of difficulty tracking down any information on it, but a colleague, Walter "doc" Urbaniak, had some information about.

Apparently CTP is in the original Xerox "Blue Book" ethernet specification, but does not seem to be documented anywhere else.


It appears that DEC tended to implement CTP on their hosts, and cisco implements it on their routers. That's sufficient for it to be useful, but it would be nice to have more information.

Protocol features

In addition to a simple loopback protocol, CTP also allows the layer 2 equivlanet of loose source routing. This is handy for making topology measurements, etc.

Protocol specification

I scanned in my photocopies of the specification, and here it is. Unfortunately I don't have good OCR capability, but if someone would care to OCR it for me, I'd appreciate it and will put it up here.
Last modified on $Date: 2001/10/16 19:40:15 $ (UTC) by $Author: jhawk $.