Loopback Plug

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What Does Loopback Plug Mean?

A loopback plug is a device used to test ports (such as serial, parallel USB and network ports) to identify network and network interface card (NIC) issues. Loopback plug equipment facilitates the testing of simple networking issues and is available at very low costs. A loopback plug device is classified as male or female.


A loopback plug is also known as a loopback adapter or loopback cable.

Techopedia Explains Loopback Plug

A loopback plug is a 10-inch wire device with a small plastic connector at one end that isolates network circuit issues and is made with RJ-45 connectors, a crimping device and unshielded twisted pair (UTP) cables.

Generally, outgoing data signals are redirected to the system, which ensures system data transmission capability. As data is looped, the system recognizes output data as input data.
Loopback plugs are generally used to route electronic signals and digital data streams from the source back to the same origin to test data transmission. Telecommunications, serial interfaces, virtual network interfaces and networking all implement loopback techniques.

Loopback techniques include:

  • Access lines are tested for transmission from the serving switching center without manual assistance.
  • The installation of a patch cable, which may be applied manually, automatically, remotely or locally.
  • The testing a communication channel with only one end point, so that any transmitted message is received by the same communication channel.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.