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Article Id 279774


This article provides some technical specs on the 'Self-Loopback' cable mentioned in HQIP hardware tests.
The details below should help to use the proper cable.








The Self-loopback cable is a special wired cable where the TX lane and RX lanes are 'looped' as illustrated below:


Self Loopback Cable.png

For the regular cabling (Cat5, 100Mbps).

  • Orange and Orange/White are often used to transmit data and may be referred to as transmit pairs.
  • Green and Green/White are often used to transmit data and may be called receive pairs.
  • Brown and Blue ones are used for other purposes (signal mirroring/noise correction).

For the Gigabit standard over regular cabling (Cat5, 1000Mbps).

  • All 4 of the wire pairs are used for data transmission.
  • The difference is in signal level (4 levels: 00/01/10/11, instead of the regular 2: 0/1) and clock rate.


During HQIP Tests, it may be required to plug a 'SELF-LOOPBACK' into interfaces so they can be tested, and in the example below, the HA port should receive a self-loopback cable while the other ports should be plugged into each other as described. 


dia hardware test network
Network Interface Loopback Test - Please connect ethernet cables:
[HA - SELF-LOOPBACK] [MGMT - Any of PORT1...PORT16] [PORT17 - PORT18] ... [PORT23 - PORT24] [X1 - X2] [x3 - x4]
Do you want to continue this test? (y/n) (default is n) y


If it is necessary to plug a self-loopback cable during the HQIP test, use a cable with the technical specifications above.

The HQIP test checks the ports at 1000Mbps speed. If this speed is not achieved, ensure the loopback connection has all 4 wire pairs connected.


The LED will only start to blink during the 'Network Interface Detection' test. This phenomenon is normal.


... ==> Network Interface Detection

Interface MAC Linkage CurrentSpeed CurrentDuplex SettingSpeed Default(Supported)
dmz 90:6C:AC:00:00:01 Linked 1000 FULL auto (1000baseT_Full)
ha1 90:6C:AC:00:00:02 Linked 1000 FULL auto (1000baseT_Full)
ha2 90:6C:AC:00:00:03 Linked 1000 FULL auto (1000baseT_Full)

lan1 90:6C:AC:00:00:04 Not linked HALF auto (1000baseT_Full)


Fortinet does not include a self-loopback cable in the product box.

Usually, only one such cable is needed for the models with the odd number of ports.


Related article: 

Hardware troubleshooting with built-in FortiOS hardware diagnostic commands