IP Address Classes

IP Address Classes

1) Static IP address

2) Shared IP address

An IP Address is a 32-bit number that identifies a computer on the Internet. Every web site on the internet is found not by its domain name but by its IP address. When someone types the address: www.xyz.com it is translated into an IP address and then the computer is directed to that IP address which is the web site.

Now every single website has an IP address specifically allocated to it. If every site assigned a separate IP address then there could be a problem with running out of IP addresses so a lot of the sites on the server use a single IP address for multiple sites.

Thus, using more than one site on an IP address is called a Shared IP address. If a site has its own IP address, and shares with no one else, it is called a Static IP address. You can always access a site which has a static IP address by using its IP address alone, but you cannot access a site using a shared IP address by typing in the IP address alone because when you type in a shared IP address you arrive at the server but the server does not know which site you are looking for as you have not told it which domain name you want.

Requirement of static IP address:

1) The main reason to have a static IP address for your site is that, you can use SSL encryption on a static IP address only. In order to transmit sensitive data over the internet, it must be encrypted to prevent someone from intercepting the information.

2) In case if the site needed the anonymous ftp access (anyone can download files of the site), the site needs to have a static IP address.

Other than these two reasons there is no need for a site to have its own IP address.

IP Address and IP Classes

- Every host on a TCP/IP network needs to have a unique address, similar to you needing a unique address for your house. With this unique address, it is possible to send data from host to host.
- Every packet contains addressing information in the header, and the IP address in the header is used to route packets.
- If several people on your street had the same address, the post office would have a difficult time sorting mail. For a similar reason, IP addresses are unique on each network.

What is IP addressing?

IP addressing is simply configuring each TCP/IP host with a valid IP address.
For access to the Internet, a host must have an IP address that identifies not only the host address (like a house number) but also identifies the network address (like a street number). An administrator needs to be aware of proper addressing techniques so that the hosts on the network will function correctly. TCP/IP addresses are based on 32-bit addresses.

IP Address Classes

IP addresses are divided into five IP classes:

IP address class A
IP address class B
IP address class C
IP address class D
IP address class E

All IP addresses are placed in a particular class based on the decimal values of their first octets. In the first octet, an IP address can start with a decimal value between 1 and 255.

IP class A addresses have first octets with a decimal number from 1 to 127.


IP class B addresses have first octets with a decimal number from 128 to 191.


IP class C addresses have first octets with a decimal number from 192 to 223.


IP class D addresses have decimal values from 224 to 239 in the first octet, and the 4 leftmost bits are 1110.


The last IP address class of addresses is IP class E. IP class E addresses range from 240 to 255 in the first octet, and the 4 leftmost bits are 1111.


The system of IP class addresses has been set up to help ensure assignment of unique IP addresses. DHCP discover, DHCP offer, DHCP request, and DHCP acknowledgment are four steps in getting an IP address from a DHCP server.

Computer IP Address Configuration

To find out local what is My IP address and possible TCP/IP networking problem follow next steps:

• If you use win9x/ME go to start-run and type winipcfg, and then press ENTER
• For win2k/xp or vista goes to start-run (Windows Vista user goes to Windows button), type CMD and then ENTER. At the DOS prompt type ipconfig and you'll see DNS suffix, IP address, subnet mask, and default gateway. For more info type ipconfig /all
• For Macintosh select the TCP/IP control panel from the Apple menu's "Control Panels" sub-menu. The TCP/IP control panel window will open and display your IP Address.

IP Address Classes map

1st Octet Decimal Range
1st Octet High Order Bits
Network/Host ID (N=Network, H=Host)
Default Subnet Mask
Number of Networks
Hosts per Network (Usable Addresses)
1 – 126*
126 (27 – 2)
16,777,214 (224 – 2)
128 – 191
16,382 (214 – 2)
65,534 (216 – 2)
192 – 223
2,097,150 (221 – 2)
254 (28 – 2)
224 – 239
Reserved for Multicasting
240 – 254
Experimental; used for research

Note: Class A addresses to cannot be used and is reserved for loopback and diagnostic functions.

Private IP Addresses

Private IP Addresses