Configuration Testing Protocol (Loop)

It's basically a layer two "ping" equivalent.

History

Ethernet configuration testing protocol (CTP) is specified in chapter 8 of the DEC/Intel/Xerox Ethernet v2.0 specification. It doesn't appear in any IEEE 802 specification.

Protocol dependencies

Ethernet: Typically, Loop uses Ethernet as its transport protocol. The well known Ethernet type for Loop is 0x9000.

Example traffic

Frame 2 (68 bytes on wire, 68 bytes captured)
    Arrival Time: Mar 21, 2006 03:02:44.202162000
    Time delta from previous packet: 0.000415000 seconds
    Time since reference or first frame: 0.000415000 seconds
    Frame Number: 2
    Packet Length: 68 bytes
    Capture Length: 68 bytes
    Protocols in frame: eth:loop:data
Ethernet II, Src: aa:00:04:00:69:04 (aa:00:04:00:69:04), Dst: aa:00:04:00:1d:04 (aa:00:04:00:1d:04)
    Destination: aa:00:04:00:1d:04 (aa:00:04:00:1d:04)
    Source: aa:00:04:00:69:04 (aa:00:04:00:69:04)
    Type: Loopback (0x9000)
Configuration Test Protocol (loopback)
    skipCount: 8
    Function: Forward Data (2)
    Forwarding address: aa:00:04:00:1d:04 (aa:00:04:00:1d:04)
    Relevant function:
    Function: Reply (1)
    Receipt number: 1
Data (40 bytes)

Wireshark

The Loop dissector is fully functional

Preference Settings

(None)

Example capture file

SampleCaptures/configuration_test_protocol_aka_loop.pcap

Display Filter

A complete list of Loop display filter fields can be found in the display filter reference

Show only the Loop based traffic:

 loop

Capture Filter

You cannot directly filter Loop protocols while capturing. However, if you know the Ethernet type used (see above), you can filter on that one.

External links

http://www.mit.edu/people/jhawk/ctp.html

Discussion

Imported from https://wiki.wireshark.org/Loop on 2020-08-11 23:16:04 UTC