IP address

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Related to Class A network: Subnet mask, IP classes

IP address

[¦ī′pē ə‚dres]
(computer science)
A computer's numeric address, such as 128.201.86.290, by which it can be located within a network.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

IP address

(networking)
(Internet address) The 32-bit number uniquely identifying a node on a network using Internet Protocol, as defined in STD 5, RFC 791. An IP address is normally displayed in dotted decimal notation, e.g. 128.121.4.5.

The address can be split into a network number (or network address) and a host number unique to each host on the network and sometimes also a subnet address.

The way the address is split depends on its "class", A, B or C (but see also CIDR). The class is determined by the high address bits:

Class A - high bit 0, 7-bit network number, 24-bit host number. n1.a.a.a 0 <= n1 <= 127

Class B - high 2 bits 10, 14-bit network number, 16-bit host number. n1.n2.a.a 128 <= n1 <= 191

Class C - high 3 bits 110, 21-bit network number, 8-bit host number. n1.n2.n3.a 192 <= n1 <= 223

DNS translates a node's fully qualified domain name to an Internet address which ARP (or constant mapping) translates to an Ethernet address.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

IP address

(Internet Protocol address) The address of a connected device in a 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 packet (Web, email, video, etc.) 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 may have several public IPs.

In contrast, the devices within the local network use private addresses not reachable from the outside world, and the router enforces this standard. The same private address ranges are used in every network, which means every computer within the company has the identical private IP address of a computer in thousands of other companies. See private IP address and NAT.

Logical vs. Physical
An IP address is a logical address that is assigned by software residing in the router or server, and that logical address can change from time to time. For example, a laptop is likely to be assigned a new IP when it starts up in a different hotspot (see DHCP). However, there is a physical address built into every unit of hardware, which cannot change (see MAC address). In order to locate a device in an IP network, the logical IP address is converted to a physical address by a resolution protocol (see ARP).

Static and Dynamic IP
Network infrastructure devices such as servers, routers and firewalls are assigned permanent "static" IP addresses. A user's machine can also be assigned a non-changing static IP by the network administrator; however, it is generally configured to accept an address automatically (see DHCP). Internet service providers may periodically change the IPs in the modems of their home users, but business users must have consistent "static" IPs for servers that face the public. See dynamic IP address and static IP address.

Version 4 and 6 (IPv4 and IPv6)
The original IP Version 4 addressing scheme defined 32 bits to hold the IP address, and it is still widely used today. However, a larger Version 6 address was subsequently created, and both are in use. It will take a long time before the newer IPv6 is the only system in use. See IPv4 addressing.


What's My IP Address?
Various websites report the user's IP address by merely going to the site. IP Chicken is one of them.
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