This is an instructional video I made for my students, as an aid to a practical assignment.

The tutorial explains

• What a network sniffer is and how it can be used
• How to look at a network sniff and tell what happens at various layers of the network stack
• Some bits about the HTTP protocol, specifically, how it resumes a broken download

The video doesn't claim to be a comprehensive guide to network sniffers, it barely scratches the tip of the iceberg.