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Network foundations

How does data find another system and service?

Interfaces, addresses, packets, routes, transport ports and client/server roles.

Last verified
2026-09-20
Review interval
365 days
Status
In review

01 / Overview

How does data find another system and service?

A network exchange crosses several distinct decisions. An interface connects a host, an IP address identifies a network endpoint, routing selects a next hop, and a transport port identifies a service endpoint. A name such as example.test belongs to DNS and is resolved before an address can be routed.

Level
Intermediate
Units
3
Estimated time
64 min
What you will learn
  • Describe a network as connected devices exchanging data.
  • Read an IPv4 interface address with a prefix length.
  • Explain when a host uses its default gateway.
Know first
  • Computer
  • Process
  • Terminal
  • Command
Learning materials
  • Labs: available
  • Embedded practice: available
  • Visuals: 2
  • Documents: 1
  1. 01What a network connects18 min
  2. 02IP addresses and local networks22 min
  3. 03Gateway and router24 min
Start topic →

02 / Learn

Learn

  1. What a network connects

    Recognise devices, interfaces, links, clients, servers and packets before reasoning about addresses.

    Open lesson →
  2. IP addresses and local networks

    Read an interface address and prefix, then decide which destinations belong to the local network.

    Open lesson →
  3. Gateway and router

    Follow a non-local packet through the default gateway and connect the logical path to real office equipment.

    Open lesson →

03 / Concepts

Concepts

Layered observationnetwork-layered-observation
Name resolution, routing, transport and application behavior are separate boundaries that can fail independently.
Endpointnetwork-endpoint
An address, transport protocol and port together identify one transport endpoint.

04 / Commands

Commands

EnvironmentCommandPurposeLab
windowsipconfigInspect the simulated interface configuration.Available in Command Lab
linuxip addressInspect the simulated Linux interface and address.Available in Command Lab
multiping 192.0.2.25Run a simulated ICMP reachability observation.Available in Command Lab

05 / Labs

Labs

  1. Command Lab

    Deterministic browser simulator for CMD, Linux shell and PowerShell practice with virtual state.

    deterministic simulator
    Open safe simulator →

06 / Visuals

Visuals

  1. A host checks whether a destination is local and otherwise sends the packet through its default gateway to a router.

    network-path-v1

    technical-diagram · verified
    Open visual →
  2. A network infographic showing internet, modem or ONT, router and switch, with wired branches to a desktop, printer, storage and access point, then wireless links to a laptop and phone.

    small-office-network-01

    conceptual-illustration · verified
    Open visual →

06B / Documents

Documents

  1. Wireshark User's Guide

    The official current interface and workflow reference. The platform links to it instead of storing an unverified local copy.

    external reference only · external-only
    Open document →

07 / Security

Security

  1. An observed reply proves only the specific exchange that was tested; it does not prove that every route, port or application is healthy.

08 / Troubleshooting

Troubleshooting

  1. Start with interface state and address, then route, name resolution, transport endpoint and application response.

09 / Quick checks

Quick checks

Level 4dns-reachability-diagnosis

A workstation can reach 192.0.2.25 but cannot resolve app.example.test. Which subsystem should you inspect first?

A workstation can reach 192.0.2.25 but cannot resolve app.example.test. Which subsystem should you inspect first?
  1. Why is a port not the same thing as a process?

10 / GRAPH

Related concepts

Used in certifications

These links reuse canonical knowledge; the certification page does not own or duplicate the topic.

11 / Resources

Resources

  1. RFC 1034 — Domain Names: Concepts and Facilities

    RFC Editor · official-doc · free

    Resources ↗
  2. RFC 1812 — Requirements for IP Version 4 Routers

    RFC Editor · official-doc · free

    Resources ↗
  3. What Is Computer Networking?

    Cisco · official-doc · free

    Resources ↗

12 / Sources and freshness

Sources and freshness

Last verified
2026-09-20
Review interval
365 days
Source version
RFC 1122 · RFC 1812 · RFC 9293 · RFC 1034 · Cisco networking basics checked 2026-09-21