IPv4 Address Structure Summary (23.2)
The following is a summary of each topic in the chapter and some questions for your reflection.
What Did I Learn in this Module? (23.2.1)
An IPv4 address is a 32-bit hierarchical address that is made up of a network portion and a host portion. When determining the network portion versus the host portion, you must look at the 32-bit stream. The bits within the network portion of the address must be identical for all devices that reside in the same network. The bits within the host portion of the address must be unique to identify a specific host within a network. If two hosts have the same bit-pattern in the specified network portion of the 32-bit stream, those two hosts will reside in the same network.
The IPv4 subnet mask is used to differentiate the network portion from the host portion of an IPv4 address. When an IPv4 address is assigned to a device, the subnet mask is used to determine the network address of the device. The network address represents all the devices on the same network.
An alternative method of identifying a subnet mask, a method called the prefix length. The prefix length is the number of bits set to 1 in the subnet mask. It is written in “slash notation”, which is noted by a forward slash (/) followed by the number of bits set to 1. For example, 192.168.10.10 255.255.255.0 would be written as 192.168.10.10/24.
The AND operation is used in determining the network address. Logical AND is the comparison of two bits. Note how only a 1 AND 1 produces a 1. Any other combination results in a 0.
• 1 AND 1 = 1
• 0 AND 1 = 0
• 1 AND 0 = 0
• 0 AND 0 = 0
To identify the network address of an IPv4 host, the IPv4 address is logically ANDed, bit by bit, with the subnet mask. ANDing between the address and the subnet mask yields the network address.
Before taking this module, I was feeling like Marcy and Vincent. I did not have a good grasp of how the numbers in the IPv4 address were important. Did you know the 32-bit hierarchical address that is made up of a network portion and a host portion? Are you able to explore this on your own network? And who knew about ANDing and the subnet mask?
I am feeling a little more like Bob after this module and I hope you are too.