Chapter 12 - Analyzing Classful IPv4 Networks

Question 1

What are the 5 IP address classes and what are they used for?

Answer 1

Class A - First octet is 1-126 - Unicast addresses used for larger networks
Class B - First octet is 128-191 - Unicaste addresses used for medium sized networks
Class C - First octet is 192-223 - Unicast addresses used for smaller networks
Class D - First octet is 224-239 - Multicast addresses
Class E - First octet is 240-255 - Reserved for experimental purposes

Question 2

What is the default subnet mask for each unsubnetted address class?

Answer 2

Class A - 255.0.0.0
Class B - 255.255.0.0
Class C - 255.255.255.0

Question 3

True or False. Addresses in the same network have different values in the network part of the address and different values in the host part of the address.

Answer 3

False. Addresses in the same network have the same values in the network part of the address and different values in the host part of the address.

Question 4

How can you determine the different characteristics of an unsubnetted classful IP address and its network?

Answer 4

• The class can be found by looking at the first octet.
• From the above the network and host bits can be divided (e.g. Class A is 8 network 24 host) (subnet bits can be taken from the host bits if necessary)
• The network address can be found by changing an IP address’s host octets to a 0
• The first usable host address can be found by adding a 1 to the network address’s last octet
• The broadcast address can be found by changing the host octets of an address all to 255
• The last usable address can be found by subtracting 1 from the fourth octet of the network’s broadcast address

Question 5

What are some of the different uses of a subnet?

Answer 5

• To define the size of the prefix (combined network and subnet parts) part of the addresses in a subnet
• To define the size of the host part of the addresses in a subnet
• Can be used to calculate the number of hosts in a subnet
• Allows a network designer to communicate design details such as the number of subnet and host bits to the devices in a network
• Can be used to calculate the number of subnets in an entire classful network
• Can be used in binary calculations to find both the subnet ID (network address) and broadcast address

Question 6

To Find the Subnet ID using Decimal

Answer 6

Do 256 - <interesting> (=magic number) and multiply the magic number (0 IS INCLUDED) until you reach the interesting octet of the IP or the nearest number to it. This is the subnet ID.</interesting>

Question 7

To Find the Broadcast Address using Decimal

Answer 7

Do 256 - <interesting> (=magic number) and add the magic number to the interesting octet of the subnet ID then take away 1. This is the broadcast address.</interesting>