Class Based IP Addresses

IP Addresses / By

Class Based IP Addresses
Class Based IP Addresses
The IP address is 32 bits in length and is used to identify both the host address (Host id) and the address of the network (Net id) in which the host resides.
An address class is defined to allocate the minimum number of bits that are to be used as the network ID.
The remaining bits can be used to further subdivide the network using subnet masks and to define the host ID.
The first bits of the IP address specify how the rest of the address should be separated into its network and host part. There are five classes of IP addresses.
They are shown in Figure
Now the first question arises here is “Why are there different classes of IP addresses, and how can I use them?”
First of all, the Internet community has defined the different types of IP addresses in order to accommodate the needs of networks of different- different sizes.
A network with less than 255 devices (workstations, routers, printers, and so) can be assigned a Class C network address.
However, a large organization with up to 65,534 devices will need at least a Class B address. Second, as long as you are not connecting your internal network directly to the public Internet, you can use any valid Class A, B, or C address you want.
However, any device that is connected directly to the Internet, must be assigned a network ID from the Internet community.
For most private networks (intranets) on the border of the public Internet, IP addresses are either assigned dynamically or statically by an Internet Service Provider (ISP).
The ISP maintains responsibility for administering IP network IDs assigned by InterNIC.
Three examples of ISPs, which dynamically assign IP addresses, commonly used by individuals for dial-up access are CompuServe, America Online, and Prodigy.
Typically, a private network requiring access to the Internet will use a direct connection to an ISP through a router.
In these cases, the ISP will provide a network ID to the private network. This address will be a unique statically assigned address provided to the ISP from InterNIC
Class A addresses are assigned to networks with extremely large numbers of hosts (networked devices).
The MSB (most significant bit) is set to 0, and is combined with the remaining seven bits of the first octet to complete the network ID.
This leaves the last 3 octets, or 24 bits to be assigned to subnet masking and to hosts. This allows for 27-2 (126) networks each with 224-2 (16777214) hosts; a total of over 2 billion addresses.
Class B addresses are assigned to networks with no more than 65,534 (216-2) hosts (networked devices).
The MSBs (most significant bits) are set to 10, and are combined with the remaining 14 bits of the first two octets to complete the network ID.
This leaves the last 2 octets, or 16 bits to be assigned to subnet masking and to hosts .This allows for 214-2 (16382) networks each with 216-2 (65534) hosts; a total of over 1 billion addresses.
Class C addresses are assigned to small networks with a more limited number of hosts.
The MSBs (most significant bits) are set to 110, and are combined with the remaining 21 bits of the first three octets to complete the network ID.
This leaves the last octet available to be assigned to subnet masking and to hosts, That allows for 221-2 (2097150) networks each with 28-2 (254) hosts; a total of over half a billion addresses.
Class D addresses are reserved for multicast groups. Multicast addresses are assigned to groups of hosts that are cooperating or are related in some manner.
Each host in a multicast group has to be configured to accept multicast packets.
The MSBs (most significant bits) of a class D address are set to 1110. The remaining bits are uniquely assigned to each group of hosts.
Class E addresses are an experimental class of IP addresses reserved for use in the future. The MSBs(most significant bits) for class E addresses are 1111.

The IP address is 32 bits in length and is used to identify both the host address (Host id) and the address of the network (Net id) in which the host resides.
An address class is defined to allocate the minimum number of bits that are to be used as the network ID.
The remaining bits can be used to further subdivide the network using subnet masks and to define the host ID.
The first bits of the IP address specify how the rest of the address should be separated into its network and host part. There are five classes of IP addresses.
They are shown in Figure
Now the first question arises here is “Why are there different classes of IP addresses, and how can I use them?”
First of all, the Internet community has defined the different types of IP addresses in order to accommodate the needs of networks of different- different sizes.
A network with less than 255 devices (workstations, routers, printers, and so) can be assigned a Class C network address.
However, a large organization with up to 65,534 devices will need at least a Class B address. Second, as long as you are not connecting your internal network directly to the public Internet, you can use any valid Class A, B, or C address you want.
However, any device that is connected directly to the Internet, must be assigned a network ID from the Internet community.
For most private networks (intranets) on the border of the public Internet, IP addresses are either assigned dynamically or statically by an Internet Service Provider (ISP).
The ISP maintains responsibility for administering IP network IDs assigned by InterNIC.
Three examples of ISPs, which dynamically assign IP addresses, commonly used by individuals for dial-up access are CompuServe, America Online, and Prodigy.
Typically, a private network requiring access to the Internet will use a direct connection to an ISP through a router.
In these cases, the ISP will provide a network ID to the private network. This address will be a unique statically assigned address provided to the ISP from InterNIC
Class A addresses are assigned to networks with extremely large numbers of hosts (networked devices).
The MSB (most significant bit) is set to 0, and is combined with the remaining seven bits of the first octet to complete the network ID.
This leaves the last 3 octets, or 24 bits to be assigned to subnet masking and to hosts. This allows for 27-2 (126) networks each with 224-2 (16777214) hosts; a total of over 2 billion addresses.
Class B addresses are assigned to networks with no more than 65,534 (216-2) hosts (networked devices).
The MSBs (most significant bits) are set to 10, and are combined with the remaining 14 bits of the first two octets to complete the network ID.
This leaves the last 2 octets, or 16 bits to be assigned to subnet masking and to hosts .This allows for 214-2 (16382) networks each with 216-2 (65534) hosts; a total of over 1 billion addresses.
Class C addresses are assigned to small networks with a more limited number of hosts.
The MSBs (most significant bits) are set to 110, and are combined with the remaining 21 bits of the first three octets to complete the network ID.
This leaves the last octet available to be assigned to subnet masking and to hosts, That allows for 221-2 (2097150) networks each with 28-2 (254) hosts; a total of over half a billion addresses.
Class D addresses are reserved for multicast groups. Multicast addresses are assigned to groups of hosts that are cooperating, or are related in some manner.
Each host in a multicast group has to be configured to accept multicast packets.
The MSBs (most significant bits) of a class D address are set to 1110. The remaining bits are uniquely assigned to each group of hosts.
Class E addresses are an experimental class of IP addresses reserved for use in the future. The MSBs(most significant bits) for class E addresses are 1111.