Network devices: NIC, hub, switch, bridge, router, access point, modem, firewall and more

Hosts and network devices

Devices that create or finally receive data, such as PCs, servers and phones, are hosts (also called end devices). Network devices (network equipment) sit in between and move, filter or control that data.

Connecting devices

Network Interface Card (NIC)

The hardware that connects a computer to a network, wired (Ethernet port) or wireless. Each NIC has a unique MAC address. It works at layers 1 and 2.

Repeater

Signals weaken (attenuate) as they travel along a cable, which limits cable length. A repeater receives a weak signal, regenerates it and sends it on, extending the distance. It works at layer 1 and doesn't understand addresses.

Hub

A hub connects several devices into a LAN, but it simply repeats every incoming signal out of all other ports. All devices share the bandwidth and collisions are common. Types: passive (just connects), active (regenerates the signal) and intelligent (adds basic management). Hubs are obsolete and have been replaced by switches.

Bridge

A bridge joins two LAN segments and forwards a frame across only if the destination is on the other side (selective forwarding). This keeps local traffic local. It works at layer 2. Switches are, in effect, multi-port bridges.

Switch

A switch connects devices in a LAN and learns which MAC address is on which port. It sends each frame only to the port where the destination is, giving each device full bandwidth and its own collision domain. Unmanaged switches are plug-and-play; managed switches add VLANs, security features, monitoring and remote management. Layer 3 switches can also route.

Router

A router connects different networks, such as a LAN to the internet or one site to another, and forwards packets using IP addresses and a routing table. Routers sit at the boundary (gateway) between networks and keep traffic flowing across the internet. Each router interface belongs to a different network. Layer 3.

Wireless access point (AP)

An access point connects wireless devices to the wired network. It works like a bridge between radio and cable (layer 2). In offices, many APs are often managed by a central controller.

Modem

Short for modulator-demodulator. It converts the computer's digital data into a signal suitable for the provider's line (telephone, cable or fibre) and back again. Home "routers" usually combine a modem, router, switch and access point in one box.

Security and traffic devices

Firewall

A firewall enforces an access-control policy between networks, allowing or blocking traffic according to rules. It normally sits at the network's gateway to the internet, but internal firewalls between zones are increasingly common. See firewall types.

Content filter

Software or an appliance that controls which content users may reach, for example blocking malicious or inappropriate websites, often by category. Common in schools and companies.

Load balancer

Spreads incoming requests across several servers so no single server is overloaded and service continues if one fails. Common algorithms:

• Round robin: each server in turn.
• Weighted round robin: more powerful servers get more requests.
• Least connections: the server with the fewest active connections.
• Least response time: the fastest-responding server.

Packet shaper

Sits between the internal network and the outside and manages bandwidth: it can prioritise important traffic (such as voice calls or business apps) and limit less important traffic (such as large downloads).

VPN concentrator

A device built to create and manage many secure VPN connections at once, for example for hundreds of remote workers. Today this role is often built into firewalls.

Devices by OSI layer