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Networking Fundamentals · Foundational

Loopback Address

An address that refers to the local host itself; 127.0.0.0/8 in IPv4 (usually 127.0.0.1) and ::1 in IPv6.

Definition

Traffic sent to a loopback address never leaves the host; the operating system loops it back internally. Pinging 127.0.0.1 tests that the local TCP/IP stack is working, independent of the NIC or cable. Router "loopback interfaces" are a different concept: virtual interfaces with ordinary routable addresses.

Example

ping 127.0.0.1 succeeds even with the network cable unplugged.

Exam tip

A successful loopback ping proves only the local IP stack works, not the NIC or network.

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