Discovery · Lesson 04

What does each network device do?

A hub, switch, router, server, access point, modem, firewall, proxy, and load balancer can all sit in the same journey, but they do different work at different boundaries.

The device question

Do not classify a device by its box.

A home box may contain a modem, router, Ethernet switch, Wi-Fi access point, firewall, DHCP server, and DNS forwarder at once. The useful distinction is the role: what information the device reads, what decision it makes, and which boundary it crosses.

Equipment forwards, filters, translates, or serves.An endpoint consumes or produces application data; an intermediary changes how that data travels or whether it is allowed to continue.

Build the model

The same network contains endpoints and intermediaries.

01

Hub

A physical-layer repeater: it sends an incoming signal out every other port. It does not learn MAC addresses or choose a destination.

02

Bridge / switch

A link-layer device that learns source MAC addresses and forwards frames toward the appropriate local port. A switch is a multi-port bridge.

03

Router

A network-layer device that compares destination IP addresses with routes and forwards packets toward a next hop.

04

Client / server

Endpoints run applications. A client starts a conversation; a server listens for a service and returns data, although one machine can do both.

05

Access point

Bridges Wi-Fi clients to a local wired network while coordinating radio access. It is not automatically the router.

06

Modem

Terminates an access technology by converting signals and synchronizing with provider equipment. It does not necessarily route IP traffic.

07

Firewall / proxy

A firewall enforces a traffic policy; a proxy terminates or relays an application exchange and may inspect, cache, or authenticate it.

08

Load balancer

Receives a service request and selects a healthy backend. It can operate at transport or application level.

Architecture diagrams

The same roles can be wired together in different ways.

These diagrams show common arrangements. They are models, not mandatory physical layouts: one appliance can combine several of these functions.

Home network

The provider link ends at the modem or ONT. A home gateway often combines router, switch, access point, firewall, DHCP, and NAT.

Campus network

Access switches connect endpoints and access points. Distribution or core routers connect local segments and external networks.

Service path

After routing reaches the service boundary, a proxy or load balancer may create a new application or transport connection to a backend.

link or forwarding roledecision or boundaryapplication endpoint

One request

Follow the roles, not just the cables.

A laptop requests a web service from a server. The exact deployment varies, but the responsibilities can be separated:

ClientCreates the HTTP request.
Access point or switchMoves the local frame using link-layer information.
Router / gatewayChooses the next network using an IP route.
Firewall or proxyApplies policy or terminates and relays the exchange.
Load balancerSelects a backend that can serve the request.
ServerRuns the application and produces the response.

The return path reverses the roles, but not always the exact devices: a proxy or load balancer may create a new connection, while a switch usually forwards frames without understanding HTTP.

Mini investigation

Identify the role from the evidence

Select a clue and identify the most likely role.

ROLESwitch

The device learned source MAC addresses and forwards a local frame to one port.

Knowledge check

Test your device model

Answer eight questions.

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