IPv4 Network Classes

2 Network Addresses An IP address can be split into: – network address, which specifies a specific network; – host number, which specifies a particular machine in that network. N.B. – There is NO correspondence between the parts of an IP address and its corresponding hostname.

3 Network Addresses There are 3 classes of address according to how much of the address is dedicated to each of the 2 roles (network address & host number). To determine the class of an address, look at the first octet of the dotted-decimal address.

4 Classes of Network Addresses A sample address ( ):

5 Classes of Network Addresses Class A – Octet 1: decimal value (e.g ) In a Class A address, the first octet is the network portion, so the Class A example above has a major network address of 10. Octets 2, 3, and 4 are for the network manager to divide into subnets and hosts as she sees fit. Class A addresses are used for networks that have as many as 16,581,375 hosts.

6 Classes of Network Addresses Class B – Octet 1: decimal value (e.g ) In a Class B address, the first two octets are the network portion, so the Class B example above has a major network address of Octets 3 and 4 (16 bits) are for local subnets and hosts. Class B addresses are used for networks that have between 256 and 65,536 hosts.

7 Classes of Network Addresses Class C – Octet 1: (e.g ) In a Class C address, the first three octets are the network portion. The Class C example above has a major network address of Octet 4 (8 bits) is for local subnets and hosts - perfect for networks with less than 256 hosts.

8 Classes of Network Addresses You may have noticed that the Class can be determined from the leading bits. – Class A addresses begin with 0. – Class B addresses begin with 10. – Class C addresses begin with 110.

9 Classes of Network Addresses What class are York’s IP addresses? – Here’s a sample: