Networking Fundamentals for Support Technicians
Models and addressing
Know the TCP/IP layers and what lives at each: IP addressing and routing, TCP and UDP ports, DNS name resolution, and the physical link. An IPv4 host needs four things - an address, a subnet mask (what is local), a default gateway (how to leave the subnet), and DNS servers (how to resolve names). Private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. An address in 169.254.x.x means the device could not reach DHCP.
Devices
A switch forwards traffic inside a LAN; a router forwards between networks; a firewall filters traffic; an access point bridges wireless to wired. Power over Ethernet supplies phones and cameras over the same cable. VLANs segment traffic logically without new hardware.
Wireless and cabling
2.4 GHz reaches farther but is crowded; 5 GHz is faster at shorter range. Use WPA2 or WPA3, never open or WEP. Ethernet categories such as Cat5e and Cat6 pair with RJ45 connectors. Bluetooth is short-range device pairing, not a LAN technology.
Troubleshooting tools
ping tests reachability, tracert or traceroute shows the path, ipconfig or ifconfig shows local configuration, nslookup queries DNS, and netstat lists connections. Work consistently top-down or bottom-up rather than jumping between layers.
Rule of thumb
If pinging an IP address works but the hostname fails, the problem is DNS. If nothing works, even by IP, check the link, the IP configuration, and the gateway. Worked example: a user browses by IP address but gets site-not-found by name - run ipconfig /all and nslookup to inspect DNS settings before touching the browser or reinstalling anything.