What is a Network Address?
A network address is used to identify individual devices on a network in much the same way that a phone number identifies an individual telephone.
The term 'network address' can refer to either of two types of network addresses.
Related Information
Logical Addresses
Consider a city name such as Rome as a logical address. Although it identifies a region of the world, it is difficult to know the exact location without more context. A person could refer to Rome, Italy or they could refer to Rome, Illinois in the U.S.
In telecommunications, an IP address is a logical address. It is a 32 bit number that is represented by four decimals separated by a period. For example 10.1.2.10 is an IP address. Every computer that is attached to the Internet has an IP address, but just like the Rome example, it is not guaranteed to identify a physical device.
Physical Addresses
The coordinates 41° 54 N' Latitude 12° 27 E' describe a unique location. It just happens to be Rome, Italy. Coordinates can be thought of as physical addresses. They describe a physical space and require no context or further clarification in order to identify a physical space.
A MAC address on computers is also known as a physical address because, unlike the IP address, a unique MAC address is written to every Ethernet network interface device in the world. No two MAC addresses are the same. A MAC address is 48 bits in length and is represented by Hexadecimal characters. An example of a MAC address is 00-1A-4D-72-D6-98 and it identifies a unique physical network card.
Example
C:\Users\itp>ipconfig /all
Windows IP Configuration
Host Name . . . . . . . . . . . . : ITP-PC001
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : it-pathways.com
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : it-pathways.com
Description . . . . . . . . . . . : Broadcom NetLink (TM) Gigabit Ethernet
Physical Address. . . . . . . . . : 84-2B-2B-94-5F-FF < Physical Address
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::e979:44bd:1d74:4797%10(Preferred)
IPv4 Address. . . . . . . . . . . : 192.168.1.100 < Logical Address
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : Saturday, 5 May 2012 7:34:18 PM
Lease Expires . . . . . . . . . . : Sunday, 6 May 2012 9:00:07 AM
Default Gateway . . . . . . . . . : 192.168.1.254 < Logical Address of Modem
DHCP Server . . . . . . . . . . . : 192.168.1.254
DHCPv6 IAID . . . . . . . . . . . : 243542827
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-15-00-DF-AF-84-2B-2B-94-5F-FF
DNS Servers . . . . . . . . . . . : 192.168.1.254
NetBIOS over Tcpip. . . . . . . . : Enabled
Usage
Every time a new host (a host is any node connecting to the network, for example a computer or printer) is added to a network a new IP address is required so that the host can communicate with other devices on the network.
That IP address is associated to the physical address of the device which is burnt into the network card. Many ADSL modems today run DHCP servers and this IP address allocation occurs without manual intervention.
Note: A quick way to check the IP address of your PC is to open a command prompt (Start -> Run -> then type 'cmd') - Inside the command prompt window type 'ipconfig'. In order for a computer to connect to the Internet it must have an IP address and a default gateway. The default gateway is usually the address of the Ethernet interface of the modem.
So Why Have Two Types of Addresses?
The two types of addresses have enabled different technologies to work together seamlessly. Physical addresses can come in many different flavors, and none of the flavors can communicate with each other directly. Ethernet, ADSL and Frame Relay, for example, have their own addressing that is not compatible. IP addresses 'oversee' these technologies and permit them to communicate with each other.
So the common factor in all telecommunications is IP addresses, and this allows underlying technologies to evolve seamlessly without affecting network nodes. If a new technology was invented tomorrow that enabled 100Gb links over telephone lines, that technology could be rolled out and made to communicate with legacy technologies by way of using their common logical addresses.
