Internet Protocol (IP)

IP is a connectionless protocol. As such, it doesn’t request acknowledgements for data sent. Instead, it relies on upper-layer protocols (like TCP) to handle reliability functions. IP addresses are probably something that you’re already familiar with. More likely than not, you’ve assigned an IP address to a computer for the purpose of connecting it to the Internet, your office, or something similar. An IP address is most often displayed in what is referred to as dotted-decimal notation, for example IP addresses are made up of two main parts – the first uniquely identifies a network, and the second uniquely identifies a host on that network. Think of this as being similar to a street address. Your house (the host) has a unique address on your road (the network).

You may also be familiar with the fact that IP uses 32-bit addresses. But what does this mean? Simple, computers do just about everything in binary, representing information as a series of 0’s and 1’s. Since an IP address is 32 bits long, it can also be represented as a series of 32 1’s and 0’s. For example, the IP address can also be represented as:

11000000 10101000 00000000 00000001

Don’t worry just yet about how those numbers are generated. By the time you get through Chapter 5, I promise it will seem like the easiest thing in the world.

You’re probably also familiar with something called a subnet mask. The purpose of a subnet mask is to define which portion of an IP address represents the network, and which portion represents the host. For example, if I have an IP address of and a subnet mask of, it means that the first eight bits (referred to as the first octet) represent the network, while the last 24 bits represent a host. In this case, the network ID is 10, while the Host ID is 1.1.1. In Chapter 5 we’ll delve much further into how masks work and how they’re created. For now, it’s important that you simply understand that every IP address requires a subnet mask to be able to distinguish between the network and host portions.

Every IP network requires a unique network ID, and each host on a network requires a unique host ID. That should be simple enough for now – an IP address simply gives us information as to the network on which a unique host can be found.

In order to communicate with a host on a different network, communication requires the use of routing. IP is what is referred to as a routed or routable protocol. That simply means that if a network is configured correctly, a host on one network will be able to communicate with a host on another, with routers acting as intermediaries deciding where a packet should be sent next. We’ll take a look at routing protocols in detail in Chapter 8.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.