An Ethernet Extender (also network extender) is any device used to extend an Ethernet segment beyond its normal distance limitation (100 m for most common forms of Ethernet). These devices employ a variety of transmission technologies and physical media (copper wire, fiber-optic cable, coaxial cable).

Extenders that use copper wire include 2- and 4-wire variants using unconditioned copper wiring to extend a LANs. Network extenders use various methods (line encodings), such as TC-PAM, 2B1Q or DMT, to transmit information. While transmitting over copper wire does not allow for the speeds that fiber-optic transmission does, it allows the use of existing voice-grade copper wiring. Copper-based Ethernet extenders must be used on unconditioned wire, ie without load coils, such as unused twisted pairs and alarm circuits.