Network Troubleshooting Tools

Overview

This lecture covers troubleshooting network connectivity issues, focusing on diagnostic tools like ICMP and the ping command.

Most network problems involve failure to establish a connection to a resource, either locally or on the Internet.
Effective troubleshooting requires tools that diagnose why connections fail.

ICMP is used by devices to communicate network errors, such as unreachable destinations or expired TTL (Time To Live).
ICMP packets have a simple structure: header and data section.
The header includes the type (what kind of message), code (specific reason), checksum, and "rest of header" fields.
The data payload contains the original packet’s IP header and first 8 bytes of its data to identify the problematic transmission.
ICMP operates automatically between devices, not intended for human use directly.

Ping is a common tool that uses ICMP echo request and reply messages to test device reachability.
Sending a ping asks, “Are you there?” and expects an echo reply if the destination is reachable.
Ping is available on all major operating systems and is run from the command line.
Output shows the reply’s address, round-trip time, TTL, message size, and statistics like packet loss and response times.
On Linux/macOS, ping runs until manually stopped; on Windows, it sends four requests by default.
Command-line flags allow customization of ping behavior (number of requests, size, timing).

ICMP (Internet Control Message Protocol) — Protocol for sending network error and status messages between devices.
TTL (Time To Live) — Field that limits the lifespan of a packet in a network.
Ping — Command-line tool that checks network connectivity using ICMP echo requests/replies.
Echo Request/Reply — ICMP message types used by ping to test if a device is reachable.

Review your operating system’s ping command documentation for additional features and options.