Essential Switch, Router, and Cable Interfaces Every Network Engineer Should Know

Fiber Optic Connectors

LC – Used on SFP, XFP and XPAK transceiver modules. The connector is a small‑form factor with a latch mechanism and a 1.25 mm ferrule.

SC – Common on GBIC, X2, XENPAK modules and 100Base‑FX ports. It is a push‑pull connector with a 2.5 mm ferrule.

ST – Screw‑type connector, rarely fitted directly on network devices. It is typically used on fiber jumper cables that have an ST on one end and an SC on the other to connect a GBIC‑equipped switch to a distribution frame.

MT‑RJ – High‑density, dual‑core (0.75 mm spacing) connector designed for data‑center applications. The two fibers are held in a small sleeve and aligned by guide pins.

FC – Threaded, high‑precision connector used mainly in test equipment and high‑performance optics.

Switch Main Interfaces

RJ‑45 Ethernet ports – Standard 10/100/1000 Mbps copper ports. Example switches often provide eight such ports.

SFP (Small Form‑Factor Pluggable) ports – Require an SFP transceiver module. Modules are available in electrical (copper), multimode and single‑mode fiber variants. The choice of module depends on link distance and required bandwidth. Fiber modules use an LC connector to mate with the fiber cable.

GBIC (Gigabit Interface Converter) modules – Older interchangeable optics supporting standards such as 1000Base‑T (copper), 1000Base‑SX (multimode), 1000Base‑LX/LH (single‑mode) and 1000Base‑ZX (long‑reach).

SC fiber interface – Some switches expose a native SC port that accepts an SC‑terminated fiber directly, eliminating the need for a separate SFP module.

Combo (dual‑use) Port

Example: Huawei S2700‑9TP‑EI (DC) provides a single gigabit combo port that can operate either as an RJ‑45 copper port or as an SFP fiber port, but not both at the same time.

Console port – RJ‑45 serial port used for local device configuration via a terminal‑emulation program (e.g., HyperTerminal, PuTTY).

Router Main Interfaces

Routers combine standard LAN RJ‑45 ports with a variety of WAN‑oriented interfaces.

Synchronous Serial (SERIAL) ports

Typical designations: serial0, serial1, etc. Used for DDN, Frame Relay, X.25, PSTN and other WAN technologies. These ports support higher line rates (up to 2 Mbps) and require a DTE‑type cable such as V.35.

Asynchronous Serial (ASYNC) ports

Often labeled AUX or async0. Primarily used for modem or modem‑pool connections, providing low‑speed dial‑up access (max 115.2 kbps).

ISDN BRI (Basic Rate Interface)

Provides up to 128 kbps over ISDN lines. The interface uses an RJ‑45 physical connector, but connects to the ISDN NT1 device via an RJ‑44‑to‑RJ‑45 crossover cable. Ports are identified as BRI0, BRI1, etc.

Configuration Interfaces

Console

Serial console (usually RJ‑45) connects a PC’s serial port (or USB‑to‑serial adapter) to the router for local configuration. A terminal‑emulation program (e.g., PuTTY, Tera Term) is used to access the device’s command line.

AUX

Asynchronous RJ‑11 port intended for remote dial‑up access or for attaching an external modem. It operates in the same way as the async serial port but uses a telephone‑style connector.

Common Serial Cables

DB‑28 and DB‑15 connectors – Used for high‑speed synchronous links (V.35, V.24) and for older DTE/DCE connections.

V.24 cable

Supports both synchronous (max 64 kbps) and asynchronous (max 115.2 kbps) modes. Frequently used for console or AUX connections.

Asynchronous maximum speed: 115200 bps

Synchronous maximum speed: 64000 bps

V.35 cable

Works only in synchronous mode, supporting up to 2 Mbps. Commonly paired with Synchronous Serial ports on routers.

Other serial cables

Includes X.21 DTE, RS‑449, RS‑530 DTE, E1 (75 Ω unbalanced, coaxial, 120 Ω balanced), RJ‑45, T1 and RJ‑11 cables. These are used for specific carrier‑grade or telephony interfaces.