Networking Basics for Job Seekers: IP, DNS, Routing, Switching and Firewalls Explained Simply

The short version

Almost every IT role touches networks. If you understand how data moves from one computer to another, you can troubleshoot faster and interview with more confidence, whether you are a developer, tester, support engineer or network engineer.

The building blocks

• IP address: the address of a device on a network, like a house number
• Subnet: a group of addresses that belong together, like one street
• Gateway and router: the exit and traffic police between streets and cities
• Switch: connects devices inside the same local network
• DNS: the phone book that turns names such as a website into IP addresses
• DHCP: automatically hands out IP addresses to devices
• Firewall: a security guard that allows or blocks traffic by rules
• NAT: lets many private devices share one public IP address
• VPN: a secure tunnel over the internet

What happens when you open a website

1. Your device asks DNS for the IP address of the site.
2. Your device sends the request to your router (default gateway).
3. The router passes it across the internet to the website's server.
4. A secure connection is set up (HTTPS).
5. The server sends back the page, and your browser shows it.

The OSI and TCP/IP models in one minute

Think of the seven OSI layers as the steps a letter takes: write it, put it in an envelope, address it, deliver it and have it opened. Interviewers use the model to see if you can locate a problem, for example a cable fault (physical layer) versus a wrong IP (network layer).

TCP vs UDP

• TCP: reliable, ordered delivery, used for web pages and file transfers
• UDP: faster, no guarantee, used for calls, video and gaming

Basic troubleshooting commands

• ping: is the other device reachable?
• ipconfig or ifconfig: what is my IP, gateway and DNS?
• tracert or traceroute: where along the path does it fail?
• nslookup: is DNS working?
• netstat: what connections are open?

A troubleshooting routine you can use

1. Check cables, Wi-Fi and the device's own network status.
2. Check that you have a valid IP address.
3. Ping the gateway, then an outside IP such as a public DNS server.
4. If outside IPs work but names do not, check DNS.
5. Check firewall rules or proxy settings if only some sites fail.

Next step

Install a free network simulator and build a two-network lab this week. Then register on JobKarle and apply to network and support roles.