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Learn Firewall Foundations

Learn how a firewall reads a packet, then write precise rules, order them, group networks into zones, publish a server from a DMZ, translate addresses with source and destination NAT, and troubleshoot a policy from evidence. Every lesson shows the same idea on nftables, FortiGate and Huawei USG. Two projects end in a complete configuration for a small company. Rules run against test packets in a bounded in-memory model; no real firewall or network is contacted.

20 lessons6 modules4.3 hours of practice4 challenges
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No installation. Your code runs right in the browser. Networking Foundations or the same knowledge: IP addresses, subnets, ports, and the difference between TCP and UDP. The rule format is a Code Temper teaching format, not the syntax of a product; the lessons show the nftables, FortiGate and Huawei USG equivalents, which you should confirm against the documentation of your version.

What you will be able to do

Course outline

Module 1

How a firewall thinks

Read packets, write precise rules, order them, and follow the reply.

  1. A firewall decides packet by packetThe five values & implicit deny · 10 min
  2. The first matching rule winsRule order & shadowed rules · 11 min
  3. Describe who and what preciselyNetworks, hosts & ports · 12 min
  4. Stateless or stateful: who lets the reply in?Return traffic & session tracking · 12 min
Module 2

Rule sets you can maintain

Log what matters, remove dead rules, and replace rules that are too wide.

  1. Log what mattersLogging & the cleanup rule · 11 min
  2. Remove rules that do nothingShadowed & redundant rules · 12 min
  3. Replace a rule that is too wideLeast privilege · 12 min
Module 3

Zones and policies

Group networks into zones, publish a server from a DMZ, and protect the firewall itself.

  1. Group networks into zonesZones & direction · 11 min
  2. Publish a server from the DMZDMZ & containment · 12 min
  3. Protect the firewall itselfManagement access · 11 min
  4. Project: a policy for a small officeProject · zones, services & logging · 20 min
Module 4

Address translation

Hide private addresses, forward a public port, and order NAT and policy correctly.

  1. Hide private addresses behind one public addressSource NAT · 12 min
  2. Forward a public port to a serverDestination NAT · 12 min
  3. Know what the policy seesOrder of NAT & policy · 12 min
Module 5

Troubleshooting

Find why traffic is blocked, find what should not pass, and read sessions.

  1. Find why traffic is blockedReading verdicts & logs · 12 min
  2. Find what should not get throughAuditing permissive rules · 12 min
  3. Trust the session tableSessions & reverse rules · 11 min
Module 6

Put it together

Handle a change request, review an old rule set, and build a complete configuration.

  1. Add a service without breaking the restChange requests & rule placement · 12 min
  2. Review a rule set with historyPolicy review · 14 min
  3. Project: publish a service and protect the officeCapstone · zones, NAT, order & logging · 24 min

Ready for your first line?

Every lesson is short, hands-on, and checked automatically.

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