TCP/IP overview

In this section, we'll take a look at the basics of TCP/IP, how packets are built, and the resolution processes that are in place, such as DNS and ARP.

In networking, we have two models that we commonly use: OSI and TCP/IP. As shown in the following diagram, on the left side we have the OSI model and on the right side we have TCP/IP model, and I've tried to match them up so that you can see how the different layers of each model line up with each other:

When we use Wireshark, we're commonly concerned with layers 2 through 7 of the OSI model. And most commonly when you use Wireshark, it's probably because something that's often application-related is going on or the system is running an application. Most commonly, you'll find yourself using Wireshark to diagnose problems that are in the upper layers, especially layer 7. But you can certainly use it to troubleshoot connectivity issues between devices on layer 3 or layer 2. While there are a number of TCP/IP services and protocols...