Networking & Connectivity / Knowledge library

RJ-45 — Registered Jack 45

Is commonly used informally for the modular Ethernet connector.

Acronym study batch 2 · reviewed 2026-10-20

Why learn RJ-45 — Registered Jack 45?

Is commonly used informally for the modular Ethernet connector.

Where it came from

Typical twisted-pair Ethernet uses 8P8C connectors; the historical registered jack is a different wiring definition.

• Memory aid (a learning cue, not the expansion): Forty-five goes with the familiar Ethernet plug.

Build your understanding

Work through these exercises in order. Try the task before opening a reference.

1. Without looking, expand RJ-45: Registered Jack 45.
2. Recall this memory aid: Forty-five goes with the familiar Ethernet plug.
3. Explain the practical use: Is commonly used informally for the modular Ethernet connector.
4. Explain this distinction: Typical twisted-pair Ethernet uses 8P8C connectors; the historical registered jack is a different wiring definition.
5. Identify RJ-45 in a device specification, architecture diagram, or system inventory.

Documentation and sources

• IEEE 802 LAN/MAN standards (www.ieee802.org)
• IETF Internet standards (www.rfc-editor.org)

Catalog source: technology-maxxing. This page reproduces the existing catalog’s learning material and source links.