Classes of IP Addresses

Class A - IP addresses

"Class A" IP addresses are for very large networks. The left most bit of the left most octet of a "Class A" network is reserved as "0". The first octet of a "Class A" IP address is used to identify the Network and the three remaining octets are used to identify the host in that particular network (Network.Host.Host.Host). 

The 32 bits of a "Class A" IP address can be represented as 0xxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.

The minimum possible value for the leftmost octet in binaries is 00000000 (decimal equivalent is 0) and the maximum possible value for the leftmost octet is 01111111 (decimal equivalent is 127). Therefore for a "Class A" IP address, leftmost octet must have a value between 0-127 (0.X.X.X to 127.X.X.X).

The network 127.0.0.0 is known as loopback network. The IP address 127.0.0.1 is used by the host computer to send a message back to itself. It is commonly used for troubleshooting andnetwork testing. 

Computers not connected directly to the Internet need not have globally-unique IP addresses. They need an IP addresses unique to that network only. 10.0.0.0 network belongs to "Class A" is reserved for private use and can be used inside any organization.

Class B - IP addresses

"Class B" IP addresses are used for medium-sized networks. Two left most bits of the left most octet of a "Class B" network is reserved as "10". The first two octets of a "Class B" IP address is used to identify the Network and the remaining two octets are used to identify the host in that particular network (Network.Network.Host.Host).

The 32 bits of a "Class B" IP address can be represented as 10xxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.

The minimum possible value for the leftmost octet in binaries is 10000000 (decimal equivalent is 128) and the maximum possible value for the leftmost octet is 10111111 (decimal equivalent is 191). Therefore for a "Class B" IP address, leftmost octet must have a value between 128-191 (128.X.X.X to 191.X.X.X).

Network 169.254.0.0 is known as APIPA (Automatic Private IP Addresses). APIPA range of IP addresses are used when a client is configured to automatically obtain an IP address from the DHCP server was unable to contact the DHCP server for dynamic IP address.

Networks starting from 172.16.0.0 to 172.31.0.0 are reserved for private use.

Class C- IP addresses

"Class C" IP addresses are commonly used for small to mid-size businesses. Three left most bits of the left most octet of a "Class C" network is reserved as "110". The first three octets of a "Class C" IP address is used to identify the Network and the remaining one octet is used to identify the host in that particular network (Network.Network.Networkt.Host).

The 32 bits of a "Class C" IP address can be represented as 110xxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.

The minimum possible value for the leftmost octet in binaries is 11000000 (decimal equivalent is 192) and the maximum possible value for the leftmost octet is 11011111 (decimal equivalent is 223). Therefore for a "Class C" IP address, leftmost octet must have a value between 192-223 (192.X.X.X to 223.X.X.X). 

Networks starting from 192.168.0.0 to 192.168.255.0 are reserved for private use.

Class D- IP addresses

Class D IP addresses are known as multicast IP addresses. Multicasting is a technique developed to send packets from one device to many other devices, without any unnecessary packet duplication. In multicasting, one packet is sent from a source and is replicated as needed in the network to reach as many end-users as necessary. You cannot assign these IP addresses to your devices.

Four left most bits of the left most octet of a "Class D" network is reserved as "1110". The other 28 bits are used to identify the group of computers the multicast message is intended for.

The minimum possible value for the left most octet in binaries is 11100000 (decimal equivalent is 224) and the maximum possible value for the leftmost octet is 11101111 (decimal equivalent is 239). Therefore for a "Class D" IP address, leftmost octet must have a value between 223-239 (223.X.X.X to 239.X.X.X).

Class E -IP addresses

Class E is used for experimental purposes only and you cannot assign these IP addresses to your devices.

Four left most bits of the left most octet of a "Class E" network is reserved as "1111".

The minimum possible value for the left most octet in binaries is 11110000 (decimal equivalent is 240) and the maximum possible value for the leftmost octet is 11111111 (decimal equivalent is 255). Therefore for a "Class E" IP address, leftmost octet must have a value between 240-255 (240.X.X.X to 255.X.X.X).

Limited Broadcast

255.255.255.255 is used to send messages to all devices in the LAN and this IP addrress is known as limited broadcast IP address.

You have learned IP addresses, different classes of IP addresses, Class A IP address, Class B IP address, Class C IP address, Class D IP address, Class E IP Address, public IP address, private IP address, multicast IP address, Limited broadcast IP address and Automatic Private IP Addresses (APIPA).