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across the Internet until one gateway recognizes the packet as belonging to a computer within its
immediate neighborhood or domain. That gateway then forwards the packet directly to the computer
whose address is specified.
Because a message is divided into a number of packets, each packet can, if necessary, be sent by a
different route across the Internet. Packets can arrive in a different order than they were sent. The
Internet Protocol just delivers them. It's up to another protocol, the Transmission Control Protocol (TCP)
to put them back in the right order. IP is a connectionless protocol, which means that there is no
continuing connection between the end points that are communicating. Each packet that travels through
the Internet is treated as an independent unit of data without any relation to any other unit of data. (The
reason the packets do get put in the right order is because of TCP, the connection-oriented protocol that
keeps track of the packet sequence in a message.) In the Open Systems Interconnection (OSI)
communication model, IP is in Layer 3, the Networking Layer. The most widely used version of IP today is
IP version 4 (IPv4). However, IP version 6 (IPv6) is also beginning to be supported. IPv6 provides for
much longer addresses and therefore for the possibility of many more Internet users. IPv6 includes the
capabilities of IPv4 and any server that can support IPv6 packets can also support IPv4 packets.
IVL.
Independent VLAN Learning (IVL) allows unicast address-to-port mappings to be created based on
a MAC Address in conjunction with a VLAN ID.
.
J
Joint Test Action Group.
An IEEE group that specifies test framework standards for electronic logic
components.
JTAG.
See “Joint Test Action Group” on page 298.
LAN.
See “Local Area Network” on page 298.
LDAP.
See “Lightweight Directory Access Protocol” on page 298.
Lightweight Directory Access Protocol.
A set of protocols for accessing information directories.
LDAP is based on the standards contained within the X.500 standard, but is significantly simpler. Unlike
X.500, LDAP supports TCP/IP, which is necessary for any type of Internet access. Although not yet
widely implemented, LDAP should eventually make it possible for almost any application running on
virtually any computer platform to obtain directory information, such as e-mail addresses and public keys.
Because LDAP is an open protocol, applications need not worry about the type of server hosting the
directory.
Learning.
The bridge examines the Layer 2 source addresses of every frame on the attached networks
(called listening) and then maintains a table, or cache, of which MAC addresses are attached to each of
its ports.
Link-State.
In routing protocols, the declared information about the available interfaces and available
neighbors of a router or network. The protocol's topological database is formed from the collected
link-state declarations.
Local Area Network.
A group of computers that are located in one area and are connected by less
than 1,000 feet of cable. A typical LAN might interconnect computers and peripherals on a single floor or
in a single building. LANs can be connected together, but if modems and telephones connect two or more
LANs, the larger network constitutes what is called a WAN or Wide Area Network.
M
MAC.
(1) Medium Access Control. In LANs, the sub-layer of the data link control sublayer that supports
medium-dependent functions and uses the services of the physical layer to provide services to the logical
link control (LLC) sublayer. The MAC sublayer includes the method of determing when a device has
access to the transmission medium. (2) Message Authentication Code. In computer security, a value that
is a part of a message or accompanies a message and is used to determine that the contents, origin,