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Diagnostic Tools & ICMP
The toolkit for finding where a network breaks, plus the ICMP types ping and traceroute rely on.
// tools
| ping | ICMP echo — reachability & RTT |
| traceroute / tracert | Hop-by-hop path via TTL |
| nslookup / dig | DNS queries & records |
| ipconfig / ip / ifconfig | Interface configuration |
| arp -a | View ARP / MAC cache |
| netstat / ss | Sockets & listening ports |
| tcpdump / Wireshark | Packet capture & analysis |
| nmap | Port & host scanning |
| iperf | Throughput testing |
// ICMP types
| 0 | Echo Reply |
| 3 | Destination Unreachable |
| 5 | Redirect |
| 8 | Echo Request |
| 11 | Time Exceeded (TTL=0) |
// extended toolkit
| iperf3 | Throughput / bandwidth testing |
| mtr | Continuous traceroute + loss per hop |
| nmap | Port & service discovery |
| netcat (nc) | Raw TCP/UDP connections & listeners |
| arp / ip neigh | View or clear the ARP cache |
| ss / netstat | Sockets & listening ports |
// troubleshooting method (7 steps)
1Identify the problem
2Establish a theory of probable cause
3Test the theory
4Plan of action / escalate
5Implement the solution
6Verify full functionality
7Document findings