Learning outcomes
- Explain the key principles of network diagnostics and packet analysis.
- Carry out a structured practical check or configuration task.
- Recognise common faults, risks and evidence needed for diagnosis.
Module 9 · Lesson 3
Network diagnostics and packet analysis
Use ping, ARP, traceroute, port tests, switch counters and packet captures to diagnose communications.
Before you begin
Laptop with approved tools and a mirrored switch port or lab tap.
Safety: Use site procedures, approved test equipment and competent supervision. Never bypass a protection or interlock without formal control.
Step-by-step learning
- Check link and switch-port status before software settings.
- Ping locally, then across the gateway, and inspect ARP resolution.
- Test the required TCP/UDP port, not only basic reachability.
- Capture traffic and filter by device, protocol and transaction.
Ian's practical tips:
- Ping proves ICMP reachability, not that the application protocol works.
- Packet captures are timestamps of truth—keep them with the fault report.
Fault-finding questions
- What should be happening, and what evidence proves it?
- Where is the last known correct signal, voltage, state or process condition?
- What changed immediately before the fault?
- Can the system be divided into smaller testable sections?
Practical activity
Create a one-page test record for this lesson. Include expected values, measured results, equipment used, risks controlled, defects found and the final proven condition.