Advanced, Wired Enterprise Networking Architectures, P5 of 5
Network Monitoring Architectures
Even small enterprise networks can grow to become complex, cantankerous beasts teeming with bewildering, mysterious messages. Misbehaving devices can "blather" on the network and interfere with valid traffic. Improperly configured software applications or "drivers" can attempt communication on nonexistent subnets or with incompatible protocols. Malicious Internet traffic can attempt to wriggle into your PCs through the network. Firewalls can block traffic inappropriately. Neighbors can connect by WiFi and steal bandwidth or they could inadvertently stumble into your network and interfere innocently.
All of these situations call for some ability to monitor your own network traffic, and it's surprisingly easy to do so. This page contains video explanations of the LAN architectures, based on "Ethernet Hubs", that help you when you need to monitor or debug network traffic.