Terminal.Drill Get the app
ch07 · operator · 95-130 min

networking and firewall evidence

Separate interface, route, DNS, socket, HTTP, and firewall evidence.

You can walk a network symptom from local host state to application reachability.

networkingdnscurlssfirewalld
Teaching diagramch07 · mental model
walk the symptom down the ladderaddress + routeip addr / ip routename (DNS)dig +shortsocketss -tulpnHTTP responsecurl -I / -veach step proves ONE layergreen here does not prove green therefirewallfirewall-cmd --list-allaudit before editruntime vs permanentping reaching a host does not prove the application answers

shows: The diagnostic ladder for a reachability symptom: address and route, then DNS name resolution, then listening socket, then HTTP response, with firewall audited separately, and each command proving only its own layer.

does not prove: It does not prove the failure is single-layer: more than one layer can be broken at once, and a green check at one step is evidence for that step only, not proof the whole path works.

Lessons in this chapter

  1. ch07/l01 Address and route before packets ip route Check local interface and routing state before blaming services.
  2. ch07/l02 DNS, sockets, and HTTP are separate curl -I Distinguish name resolution, listening sockets, and application responses.
  3. ch07/l03 Firewall state without accidental changes firewall-cmd --list-all Audit zones, services, ports, runtime, and permanent rules before editing.
capstone

network diagnostic ladder

Diagnose a sample reachability problem across address, route, DNS, socket, HTTP, and firewall layers.

Deliverable

A ladder with one command, observation, and conclusion per layer.

Success criteria

  • DNS and HTTP are not conflated.
  • Socket state is included.
  • Firewall changes are proposed only after audit.
Terminal Drill companion

Networking

After you can say which layer failed and which command proved it.

Train after the lesson

Failure -> diagnosticScenario -> next checkOutput -> explanation