rotocol address) The address of a connected device in an IP network (TCP/IP network), which is the worldwide standard both in-house and on the Internet. Every desktop and laptop computer, server, scanner, printer, modem, router, smartphone, tablet and smart TV is assigned an IP address, and every IP packet traversing an IP network contains a source IP address and a destination IP address.
Public and Private Addresses
For homes and small businesses, the entire local network (LAN) is exposed to the Internet via one public IP address. Large companies have several public IPs.
In contrast, the devices within the network use private addresses not reachable from the outside world, and the router enforces this standard. The same private IP address ranges are used in every network. Therefore, every computer in a company is assigned the same private IP address as a computer in thousands of other companies. See private IP address
Logical vs. Physical
An IP address is a logical address that is assigned by software residing in a server or router (see DHCP
). The physical address is built into the hardware (see MAC address
). In order to locate a device in the network, the logical IP address is converted to a physical address by a resolution protocol within the TCP/IP suite of protocols (see ARP
). An IP address can be changed because it is assigned, but the physical MAC address is hardwired into the device.
Static and Dynamic IP
Network infrastructure devices such as servers, routers and firewalls are typically assigned permanent "static" IP addresses. The client machines can also be assigned static IPs by a network administrator, but most often are automatically assigned "dynamic" IP addresses via software in the router (see DHCP
). Internet service providers may change the IPs in the modems of their home users here and there, but business users must have consistent "static" IPs for servers that face the public. See dynamic IP address
The Dotted Decimal Address: x.x.x.x
IP addresses are written in "dotted decimal" notation, which is four sets of numbers separated by decimal points; for example, 126.96.36.199. Instead of the domain name of a website, the actual IP address can be entered into the browser. However, the Domain Name System (DNS) exists so users can enter computerlanguage.com instead of an IP address, and the domain (the URL) computerlanguage.com is converted to the numeric IP address (see DNS
Although the next version of the IP protocol offers essentially an unlimited number of unique IP addresses (see IPv6
), the traditional IP addressing system (IPv4) uses a smaller 32-bit number that is split between the network and host (client, server, etc.). The host part can be further divided into subnetworks (see subnet mask
Class A, B and C
Based on the split of the 32 bits, an IP address is either Class A, B or C, the most common of which is Class C. More than two million Class C addresses are assigned, quite often in large blocks to network access providers for use by their customers. The fewest are Class A networks, which are reserved for government agencies and huge companies.
Although people identify the class by the first number in the IP address (see table below), a computer identifies class by the first three bits of the IP address (A=0; B=10; C=110). This class system has also been greatly expanded, eliminating the huge disparity in the number of hosts that each class can accommodate (see CIDR
). See private IP address
NETWORKS VS. HOSTS IN IPV4 IP ADDRESSES
Range Maximum Maximum Bits
Class Networks Hosts Net/Host
A 1-126 127 16,777,214 7/24
B 128-191 16,383 65,534 14/16
C 192-223 2,097,151 254 21/8
127 reserved for loopback test
Networks, Subnets and Hosts
An IP address is first divided between networks and hosts. The host bits are further divided between subnets and hosts. See subnet mask