If you're just getting started in the networking field, you've got a lot to learn, and with the rate of changes in networking technology, you can expect to always have a lot to learn, but here are ten essential topics that you should concentrate on (and if you are not just getting started, here are some things to review):
- The OSI model: Memorize it. It's almost a cliché, but understanding it is critical.
- TCP/IP concepts: Learn to think in binary and get a firm grasp on bitmasks, subnetting, gateways (like the "default gateway") and how addresses are constructed (the network portion, the host portion, etc).
- Stacks: Read about how the network stack is implemented on hosts. Get a good feel for what each component (the NIC, firmware, device drivers, the OS, etc) is responsible for. Once you understand this, troubleshooting is easy.
- Layer 2: Learn how switches operate and how they're different from hubs and routers. Understand bridging, and get a general idea of what Spanning Tree Protocol does. Learn the difference between a collision domain and a broadcast domain, and then study VLANs.
- Routing: Learn a routing protocol. Start with RIP, because it's easy. You don't need to be a guru, just get a general idea about how routers can exchange information about the network.
- Services: Understand the role of DNS and DHCP and WINS and know their alternatives, like the host and lmhost files and static addressing.
- Find yourself some good networking reference material. Whatis.com is a great for deciphering arcane acronyms.
- Security: Read a little about how firewalls operate and other security technologies like VPNs. Understand the difference between authentication, authorization and accounting.
- Output: Learn how to get status and information out of your networking devices. A good place to start is with the "show" commands (which will be featured in next week's tip).
- Finally, do a walkthrough: follow data as it goes from one application to another. How does it get from the application, to being segmented, packetized, framed, and routed? How does your computer know what IP address to send the packet to? (DNS) How does it know what MAC address to send it to? (ARP) How does it know how big to make the frame? (MTU) How does a switch know which port to forward your packet out on? (FDB) How does a router know which interface to use? (routing table) If you can answer these questions, you're well on your way to being competent and productive.
Tom Lancaster, CCIE# 8829 CNX# 1105, is a consultant with 15 years experience in the networking industry, and co-author of several books on networking, most recently, CCSPTM: Secure PIX and Secure VPN Study Guide published by Sybex.