TCP/IP Primer, Part I - IP Addresses

All references to IP imply IPv4, the new expanded IPv6 protocol with it's expanded IP address range and different IP address notation will not be considered

in this primer.
The TCP/IP suite of protocols uses the IP protocol to handle all addressing and routing issues. An IP address is a unique number that identifies each host

(computer or TCP/IP device) to the network. The IP address is made up of 2 parts called the network ID and the host ID. The network ID identifies the

network on which the host is located. The host ID is the identifier for the host on that network.
The IP address is a 32 bit number. An example of an IP address in binary would be:
11000000 10101000 00000001 00000011

To make IP addresses easier to read they are represented as four 8 bit numbers that are converted to decimal format and separated using periods ("."). This

format is referred to as dotted decimal notation. Thus the address above would be shown as:

This address is made up of the nework and host IDs. The diagram below illustrates this example IP address in both binary and dotted decimal notation and

shows the network and host ID parts of the address. Each group of 8 bits is referred to as an octet. Thus an IP address is made up of 4 octets.
11000000  10101000   00000001  00000011

|<------------------------->| |<---->|
Network ID Host ID
192 . 168 . 1 . 3

There are two special case addresses that cannot be used for any device on a network. These addresses are called the network address and the broadcast

address. The network address for any given network is the network ID and all zeros in the host ID. Thus for our example above, the network address would

11000000 10101000 00000001 00000000

The broadcast address is a special address used when one node wants to send something to all other nodes on the same local network. The broadcast address

consists of the network ID and all ones in the host ID. Thus for our example, the broadcast address would be:
11000000 10101000 00000001 11111111

Neither of these addresses should ever be used for nodes on the network.

Subnet Masks

Network IDs and host IDs are identified using a subnet mask which is a series of 1s and 0s that match the network and host portion of the address

respectively. Thus for a C class IP address, the subnet mask would be:

11111111 11111111 11111111 00000000

In dotted decimal notation this would be:

So, for class A, B and C addresses, the corresponding subnet masks would be:

Class Subnet Mask in Binary Subnet Mask in Decimal
A 11111111 00000000 00000000 00000000
B 11111111 11111111 00000000 00000000
C 11111111 11111111 11111111 00000000

These subnet masks are the default masks for their respective class. Customizing the subnet mask for a given network is called subnetting. You subnet a

network when you need to create more than one network from a single network. To connect networks together you need a device called a router which moves IP

packets from one IP network to another.

Continue to [url=]TCP/IP Primer, Part II - Classless Inter-Domain Routing


TCP/IP Primer, Part I - IP Addresses

Edited by sealeopard (2004-03-11 03:46 PM)
There are two types of vessels, submarines and targets.