1. IPv4 Network Classes

2. 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. 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. 4 Classes of Network Addresses A sample address (148.78.250.12):

5. 5 Classes of Network Addresses Class A – 00000000 - 01111111 Octet 1: decimal value 0-127 (e.g. 10.1.23.19) 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. 6 Classes of Network Addresses Class B – 10000000 - 10111111 Octet 1: decimal value 128-191 (e.g. 172.16.19.48) 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 172.16 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. 7 Classes of Network Addresses Class C – 11000000 - 11011111 Octet 1: 192-223 (e.g. 193.18.9.10) In a Class C address, the first three octets are the network portion. The Class C example above has a major network address of 193.18.9. Octet 4 (8 bits) is for local subnets and hosts - perfect for networks with less than 256 hosts.

8. 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. 9 Classes of Network Addresses What class are York’s IP addresses? – Here’s a sample: 130.63.236.200