Configuration Testing Protocol (Loop)
It's basically a layer two "ping" equivalent.
History
Ethernet configuration testing protocol (CTP) is a part of the original Ethernet specification that doesn't appear in IEEE 802.*
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