Week 09 · lesson
Lesson 4: Complete Network Symptom Lab
Core path: 42 minutes
Every station uses supplied evidence. No live scanning or school-network configuration changes are required.
Station A: intermittent wireless connectivity
Evidence includes fluctuating signal/interference and repeated disconnects. Compare AP/client distance, channel use, neighboring interference, and wired uplink evidence.
Station B: slow network speed
Separate endpoint resource issues, negotiated link/path limits, congestion, Wi-Fi conditions, and remote-service performance. "Slow internet" is not automatically an ISP failure.
Station C: limited connectivity
Endpoint has local association/link but cannot reach expected destinations. Use address, subnet, gateway, DHCP, DNS, and local/remote comparisons.
Station D: jitter and poor VoIP quality
Supplied voice traffic shows variable packet delay. Explain why jitter can damage real-time call quality even when average bandwidth appears sufficient.
Station E: port flapping
A switch-port status repeatedly transitions up/down in the supplied log. Investigate media, connector, endpoint NIC, switch port, power, or physical instability before changing DNS.
Station F: high latency
Connectivity succeeds but response delay is high. Use path-hop/timing evidence to separate latency from complete packet/path failure.
Station G: external interference
Wi-Fi signal exists but performance degrades when a competing/interfering source is active. Use supplied analyzer/channel evidence rather than guessing from signal bars alone.
Station H: authentication failure
Wireless association or service access reaches an authentication boundary but credentials/policy are rejected in the fictional evidence. Do not diagnose RF failure when the authentication exchange is the failed boundary.
Station I: intermittent internet connectivity
Local LAN remains stable while upstream/provider path repeatedly disappears. Separate local switching/Wi-Fi evidence from router/WAN/provider evidence.
Lab record
For at least six stations complete:
symptom:
last proven-good boundary:
first failed/unproven boundary:
tool/evidence selected:
strongest theory:
alternative theory:
controlled next action:
verification:Success criteria
A passing lab distinguishes all named 5.5 symptoms and uses the evidence path to avoid one-size-fits-all fixes.
Find a wrong default gateway
Local addressing and the router interface work, but the default route points to the wrong subnet. Use route evidence, correct one simulated value, and verify remote reachability.
Ghostty Web renders the terminal, but this lesson still uses a controlled Robotnix command engine. No unrestricted operating-system shell is connected.
ip addrip routeping -c 2 192.168.10.1ping -c 2 203.0.113.10ip route replace default via 192.168.10.1
Read a deterministic terminal transcript
This fallback runs the same bounded Robotnix simulation against the suggested command sequence. It does not connect to an operating-system shell or network.
Robotnix gateway diagnosis simulation
All addresses are documentation/simulated values. No packets leave the browser.
$ ip addr
2: eth0: <UP> mtu 1500
inet 192.168.10.25/24 brd 192.168.10.255
$ ip route
default via 192.168.20.1 dev eth0
192.168.10.0/24 dev eth0 scope link
$ ping -c 2 192.168.10.1
64 bytes from 192.168.10.1: icmp_seq=1 ttl=64 time=0.7 ms
64 bytes from 192.168.10.1: icmp_seq=2 ttl=64 time=0.8 ms
$ ping -c 2 203.0.113.10
From 192.168.10.25 icmp_seq=1 Destination Host Unreachable
2 packets transmitted, 0 received, +1 errors, 100% packet loss
$ ip route replace default via 192.168.10.1
Default route replaced in simulated state.Read it. Prove it.