// Mission Fieldwork 01

How Networks Work

Watch one web request travel from your browser to a server and back. Then build the real thing in Linux and see it happen yourself.

Free · No signup 18 sessions · About 6 hours · Self-paced with video and labs
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// The route

The whole course, at a glance.

Three acts, eighteen sessions. Every title below jumps straight to that session.

Prefer missions to lessons? Acts 1 and 2 are also playable as Signal Path I: Browser to Server, 24 guided missions, same material, no terminal.

// Before you begin

Start with curiosity, not credentials.

Begin in the browser. When the route reaches a real lab, use a clean Ubuntu VM or WSL2 environment. Each stage states what you need, what you will change, and what evidence to keep.

// How it works

Follow the Signal Path in order.

Each stop moves through the Mission Fieldwork loop: see the model, operate the tool, build the system, change one condition, and prove the result. Video recordings support the route; they are not the only way through it.

18-session curriculum

Understand the path, build it, then prove it.

The essential route is available here without JavaScript. Browser activities need only a current browser. Systems labs name Linux, WSL2, Ubuntu VM, or Docker requirements individually.

Act 1: Inside Your Local Network 6 sessions · Beginner · Browser, Linux, WSL2, or Ubuntu VM

  1. Follow the Packet: What Happens When You Open a Website
  2. IP Addresses: Finding Hosts and Networks
  3. Subnetting: Divide a Network Without Guessing
  4. Ethernet and MAC Addresses: Moving Data Across a LAN
  5. ARP: Turning Local IP Addresses Into MAC Addresses
  6. Ethernet Switching: Learning, Flooding, and Forwarding

Act 2: From Your LAN to an Application 6 sessions · Beginner to intermediate · Browser

  1. Routing Tables: Choosing the Next Hop
  2. NAT and Ports: Sharing One Public Address
  3. TCP, UDP, and Ports: Choosing the Transport
  4. Inside a TCP Connection: Handshake, Data, and Teardown
  5. DNS: From a Name to an IP Address
  6. HTTP and TLS: Securing the Web Request

Act 3: Operating Real Networks 6 sessions · Intermediate · Browser and Docker for the BGP lab

  1. Network Troubleshooting: Test One Layer at a Time
  2. Firewalls and Stateful Filtering: Why Reachable Is Not Allowed
  3. Load Balancers and Proxies: One Name, Many Servers
  4. Cloud Networking: VPCs, Subnets, Routes, and Gateways
  5. How the Internet Routes: ASNs, Prefixes, Transit, and Peering
  6. Your First BGP Mental Model: Routes, Neighbors, and Policy

// Video recordings

Watch the sessions on YouTube.

All recordings are free and published in order. Follow along at your own pace.

Open YouTube Playlist

// Field notes

Small facts that make packet captures click.

Each note connects an abstract idea to a value or command you can inspect yourself.

Ethernet arithmetic

1500 bytes is not the whole frame.

Add the 14-byte Ethernet header and 4-byte FCS for 1518 bytes. Preamble and inter-frame gap still consume time on the wire.

tcpdump -nn -e -r trace.pcap
Routing truth

The kernel decides before the packet leaves.

ip route get reveals the chosen route, source address and egress interface for one destination.

ip route get 1.1.1.1 ip neigh show
Capture discipline

Two filters, two languages.

A capture filter limits the PCAP. A display filter hides packets after capture. Preserve broad evidence first, then narrow the view.

tcpdump -ni any -w trace.pcap 'tcp port 443' tcpdump -nn -r trace.pcap 'tcp[tcpflags] & tcp-syn != 0'
Layer 2 state

Bridges learn from source MAC addresses.

Unknown destinations flood. Known unicasts follow the FDB, subject to VLAN membership and STP state.

bridge link show bridge vlan show bridge fdb show

// Free and open study shelf

Go deeper without buying a platform.

Project documentation, open guides and real tools, from packet reading to routing protocols.

Open-source docs

Wireshark User's Guide

Capture workflow, protocol details, statistics and display filters.

Read the official guide → Free open guide

Beej's Guide to Network Concepts

A friendly path through packets, addressing, transport and routing.

Open the guide → Open-source lab

Mininet Walkthrough

Build virtual hosts, switches and links with standard Linux tools.

Run the walkthrough → Free software docs

FRRouting User Guide

Continue from static routes into OSPF, BGP and IS-IS.

Explore FRR → Linux reference

Network namespace manual

Read the primitive behind the labs: isolated network stacks.

Read the manual → Open standard

IPv6 specification

Read the IPv6 header and extension-header rules from the source.

Read RFC 8200 →

What you can prove when you finish

You will be able to trace a request across DNS, Ethernet, IP, routing, NAT, TCP, TLS, firewalls, load balancers, and BGP, then choose evidence that distinguishes one failure from another.

Open the Toolbench →