The machine on a network is called as Host. Each TCP/IP host is identified by a unique IP Address. Internally each IP Address is separated into two parts network ID and a Host ID.
The network ID identifies a single network segment within the larger internetwork. Internetwork is a network of networks. All machines that are access to the same network have a common network ID. The host ID identifies a TCP/IP node within each network. A node may be a workstation or server or router or other TCP/IP device.
IP Addresses are four sets of 8 bits,totally 32 bits. IP Addresses are usually expressed in decimal notation instead of long binary strings. These 8 bit octets are converted to decimal numbers and separated by periods. For example 192.168.1.2 is an IP Address.
There are 5 IP Address classes. Out of these 5 three classes are used for assignment to TCP/IP nodes. They are Class A,B and C.
The IP Address class defines which bits are used for network ID and host ID parts of each address. It also defines howmany networks and hosts per network can be supported.
For example p.q.r.s represent the four octet values in any IP Address.
For Class A the value of p is 1-126. First octet p represents network ID. The remaining 3 octets q.r.s represents Host ID. Class A supports 126 networks and 16,777,214 hosts per network.
For Class B the value of p is 128-191. First two octets p.q represents network ID. The last two octets r.s represents Host ID. Class B supports 16,384 networks and 65,534 hosts per network.
For Class C the value of p is 192-223. First three octets p.q.r represents network ID. The last octet s represents Host ID. Class C supports 20,97,152 networks and 254 hosts per network.
Subnet Mask is also a 32 bit number. Subnet Mask identifies Network ID and Host ID parts within the IP Address. Subnet Mask uses bit groups of all ones to identify the network ID and uses bit groups of all zeroes to identify the Host ID parts of an IP Address.
For example take IP Address 192.168.1.2 The value of first octet is 192. So this is Class C IP Address. p.q.r represents network ID and s represents Host ID. So for above IP address network ID is 192.168.1 and Host ID is 2.
For the above IP Address Subnet Mask number is 11111111 11111111 11111111 00000000 In decimal notation it is 255.255.255.0
For Class A IP Address Subnet mask is 255.0.0.0
For Class B IP Address Subnet mask is 255.255.0.0
Note: Articles on Windows NT,Windows 2000 Server,Windows 2003 Server will come soon on my blog under the same NETWORKING section.