IP Address and Subnet Masks for the CCENT Exam
On the CCENT Exam you will come across many different topics, but a major topic that will be presented in various different questions are IP addresses.
Any computer or router (an OSI Model layer 3 device) will need to have an IP address so that the computers are capable of interacting with one another.
In order to understand the concept of how they work they can be compared to something more familiar like telephone numbers. Any phone number that you call has a specific phone dedicated to it. So, if you wanted to call your mom you would dial her number and know that she would be the one to answer.
Computers operate in a similar fashion, but instead of using a phone number to talk to a specific computer you would use its IP address, which has a 32 bit long number that is written out in dotted decimal format. Which means there is a dot (a period) between every 8 bits. This just makes it much easier to read. An example of an IP address is: 192.168.1.1. Computers convert this number to binary, but that is a whole different lesson I don’t want to get into right now. Just remember that an IP address is split up into 4 different sections.
An IP address also has what is called a subnet mask attached to the end of it. For example, one with a subnet mask look like this 192.168.1.1 255.255.255.0. The purpose of the subnet mask is to let you know which part of the IP address belongs to the network and which part belongs to the hosts. This can kind of be compared to area codes when calling somebody’s telephone number.
In the above example because of what the subnet mask tells us, the network portion is the first three octets 192.168.1 and the host portion is the last octet.1. In this example and because there are only 8 binary bits allowed for each octet you can only have 256 addresses. So, for this example you can assign up to 254 hosts on this network. The number is 254 because you need to save 2 of the addresses to specify the network address and the broadcast address.
