Short for Media Access Control address, a hardware
address that uniquely identifies each node of a network. In IEEE
802 networks, the Data Link Control (DLC) layer of the OSI Reference
Model is divided into two sublayers: the Logical Link Control
(LLC) layer and the Media Access Control (MAC) layer.
The MAC layer interfaces directly with the network media. Consequently,
each different type of network media requires a different MAC
On networks that do not conform to the IEEE 802 standards
but do conform to the OSI Reference Model, the node address is
called the Data Link Control (DLC) address.
See a breakdown of the seven OSI layers in the Quick Reference
section of Webopedia.
To find your MAC address try going to this out side link source
On a (LAN) ( Local area network)
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a TechTarget site for Networking professionals.
A local area network (LAN) is a group of
computers and associated devices that share a common communications
line or wireless link and typically share the resources of a
single processor or server within a small geographic area (for
example, within an office building). Usually, the server has
applications and data storage that are shared in common by multiple
computer users. A local area network may serve as few as two
or three users (for example, in a home network) or many as thousands
of users (for example, in an FDDI network).
The main local area network technologies
* Token Ring
* FDDI (Fiber Distributed Data Interface)
or other network, the MAC (Media Access Control) address is
your computer's unique hardware number. (On an Ethernet
LAN, it's the same as your Ethernet address.)
Ethernet is the most widely-installed
local area network (LAN) technology. Specified in a standard,
IEEE 802.3, Ethernet was originally developed by Xerox and then
developed further by Xerox, DEC, and Intel. An Ethernet LAN typically
uses coaxial cable or special grades of twisted pair wires. Ethernet
is also used in wireless LANs. The most commonly installed Ethernet
systems are called 10BASE-T and provide transmission speeds up
to 10 Mbps. Devices are connected to the cable and compete for
access using a Carrier Sense Multiple Access with Collision Detection
Fast Ethernet or 100BASE-T provides
transmission speeds up to 100 megabits per second and is typically
used for LAN backbone systems, supporting workstations with 10BASE-T
cards. Gigabit Ethernet provides an even higher level of backbone
support at 1000 megabits per second (1 gigabit or 1 billion bits
per second). 10-Gigabit Ethernet provides up to 10 billion bits
When you're connected to the Internet from your computer (or
host as the Internet protocol thinks
The term "host" is used in
several contexts, in each of which it has a slightly different
1) In Internet protocol specifications,
the term "host" means any computer that has full two-way
access to other computers on the Internet. A host has a specific
"local or host number" that, together with the network
number, forms its unique IP address. If you use Point-to-Point
Protocol to get access to your access provider, you have a unique
IP address for the duration of any connection you make to the
Internet and your computer is a host for that period. In this
context, a "host" is a node in a network.
2) For companies or individuals with
a Web site, a host is a computer with a Web server that serves
the pages for one or more Web sites. A host can also be the company
that provides that service, which is known as hosting.
3) In IBM and perhaps other mainframe
computer environments, a host is a mainframe computer (which
is now usually referred to as a "large server"). In
this context, the mainframe has intelligent or "dumb"
workstations attached to it that use it as a host provider of
services. (This does not mean that the host only has "servers"
and the workstations only have "clients." The server/client
relationship is a programming model independent of this contextual
usage of "host.")
4) In other contexts, the term generally
means a device or program that provides services to some smaller
or less capable device or program.
a correspondence table relates your IP
address to your computer's physical
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This definition is based on Internet Protocol Version 4. See
Internet Protocol Version 6 (IPv6) for a description of the newer
128-bit IP address. Note that the system of IP address classes
described here, while forming the basis for IP address assignment,
is generally bypassed today by use of Classless Inter-Domain
Routing (CIDR) addressing.
In the most widely installed level of
the Internet Protocol (IP) today, an IP address is a 32-bit number
that identifies each sender or receiver of information that is
sent in packets across the Internet. When you request an HTML
page or send e-mail, the Internet Protocol part of TCP/IP includes
your IP address in the message (actually, in each of the packets
if more than one is required) and sends it to the IP address
that is obtained by looking up the domain name in the Uniform
Resource Locator you requested or in the e-mail address you're
sending a note to. At the other end, the recipient can see the
IP address of the Web page requestor or the e-mail sender and
can respond by sending another message using the IP address it
An IP address has two parts: the identifier
of a particular network on the Internet and an identifier of
the particular device (which can be a server or a workstation)
within that network. On the Internet itself - that is, between
the router that move packets from one point to another along
the route - only the network part of the address is looked at.
The Network Part of the IP Address
The Internet is really the interconnection of many individual
networks (it's sometimes referred to as an internetwork).
So the Internet Protocol (IP) is basically the set of rules for
one network communicating with any other (or occasionally, for
broadcast messages, all other networks). Each network must know
its own address on the Internet and that of any other networks
with which it communicates. To be part of the Internet, an organization
needs an Internet network number, which it can request from the
Network Information Center (NIC). This unique network number
is included in any packet sent out of the network onto the Internet.
The Local or Host Part of the IP
In addition to the network address or number, information is
needed about which specific machine or host in a network is sending
or receiving a message. So the IP address needs both the unique
network number and a host number (which is unique within the
network). (The host number is sometimes called a local
or machine address.)
Part of the local address can identify
a subnetwork or subnet address, which makes it easier for a network
that is divided into several physical subnetworks (for examples,
several different local area networks or ) to handle many devices.
IP Address Classes and Their Formats
Since networks vary in size, there are four different address
formats or classes to consider when applying to NIC for a network
* Class A addresses are for large
networks with many devices.
* Class B addresses are for medium-sized networks.
* Class C addresses are for small networks (fewer than
* Class D addresses are multicast addresses.
The first few bits of each IP address
indicate which of the address class formats it is using. The
address structures look like this:
0 Network (7 bits) Local address (24 bits)
10 Network (14 bits) Local address (16 bits)
110 Network (21 bits) Local address (8 bits)
1110 Multicast address (28 bits)
The IP address is usually expressed
as four decimal numbers, each representing eight bits, separated
by periods. This is sometimes known as the dot address and, more
technically, as dotted quad notation. For Class A IP addresses,
the numbers would represent "network.local.local.local";
for a Class C IP address, they would represent "network.network.network.local".
The number version of the IP address can (and usually is) represented
by a name or series of names called the domain name.
The Internet's explosive growth makes
it likely that, without some new architecture, the number of
possible network addresses using the scheme above would soon
be used up (at least, for Class C network addresses). However,
a new IP version, IPv6, expands the size of the IP address to
128 bits, which will accommodate a large growth in the number
of network addresses. For hosts still using IPv4, the use of
subnets in the host or local part of the IP address will help
reduce new applications for network numbers. In addition, most
sites on today's mostly IPv4 Internet have gotten around the
Class C network address limitation by using the Classless Inter-Domain
Routing (CIDR) scheme for address notation.
Relationship of the IP Address to
the Physical Address
The machine or physical address used within an organization's
local area networks may be different than the Internet's IP address.
The most typical example is the 48-bit Ethernet address. TCP/IP
includes a facility called the Address Resolution Protocol (ARP)
that lets the administrator create a table that maps IP addresses
to physical addresses. The table is known as the ARP cache.
Static versus Dynamic IP Addresses
The discussion above assumes that IP addresses are assigned on
a static basis. In fact, many IP addresses are assigned dynamically
from a pool. Many corporate networks and online services economize
on the number of IP addresses they use by sharing a pool of IP
addresses among a large number of users. If you're an America
Online user, for example, your IP address will vary from one
logon session to the next because AOL is assigning it to you
from a pool that is much smaller than AOL's base of subscribers.
DLC also is an abbreviation for digital loop carrier.
DLC (data link control) is the service provided by the Data
Link layer of function defined in the Open Systems Interconnection
(OSI) model for network communication. The Data Link layer is
responsible for providing reliable data transfer across one physical
link (or telecommunications path) within the network. Some of
its primary functions include defining frames, performing error
detection or ECC on those frames, and performing flow control
(to prevent a fast sender from overwhelming a slow receiver).
Many point-to-point protocols exist at the Data Link layer
including High-level Data Link Control (HDLC), Synchronous Data
Link Control (SDLC), Link Access Procedure Balanced (LAPB), and
Advanced Data Communications Control Procedure (ADCCP). All of
these protocols are very similar in nature and are found in older
networks (such as X.25 networks). In the Internet, one of two
point-to-point protocols are used at this layer: Serial Line
Internet Protocol (SLIP) or Point-to-Point Protocol (PPP) with
PPP being the newer, approved standard. All of these protocols
are used in point-to-point connections such as those on metropolitan
area network (MAN) or wide area network (WAN) backbones or when
we dial our Internet service provider (ISP) from home using a
In local area networks (LANs) where connections are multipoint
rather than point-to-point and require more line-sharing management,
the Data Link layer is divided into two sublayers: the Logical
Link Control layer and the Media Access Control layer. The Logical
Link Control layer protocol performs many of the same functions
as the point-to-point data link control protocols described above.
The Media Access Control (MAC) layer protocols support methods
of sharing the line among a number of computers. Among the most
widely used MAC protocols are Ethernet (IEEE 802.3), Token Bus
(IEEE 802.4), and Token Ring (IEEE 802.5) and their derivatives