L

L2F (Layer 2 Forwarding Protocol)

A VPN protocol designed to work in conjunction with the PPP to support authentication standards, such as Terminal Access Controller Access Control System (TACACS+) and Remote Authentication Dial-In User Service RADIUS), for secure transmissions over the Internet.

L2TP (Layer 2 Tunneling Protocol)

A dial-up VPN protocol that defines its own tunneling protocol and works with the advanced security methods of IPSec. L2TP allows PPP sessions to be tunneled across an arbitrary medium to a home gateway at an ISP or a corporation.

LAN (local area network)

A group of connected computers located in a single geographic area—usually a building or campus—that share data and services.

laser printer

A type of printer that uses electrophotography as the means of printing images on paper.

latency

The delay induced by a piece of equipment or device that is used to transfer data.

learning bridge

A bridge that builds its own bridging address table rather than requiring someone to enter information manually. Most modern bridges are learning bridges. Also called a smart bridge.

legacy

An older computer system or technology.

line conditioner

A device that is used to stabilize the flow of power to the connected component. Also known as a power conditioner or voltage regulator.

link light

An LED on a networking device such as a hub, switch, or NIC. The illumination of the link light indicates that, at a hardware level, the connection is complete and functioning.

link-state routing

A dynamic routing method in which routers tell neighboring routers of their existence through packets called link-state advertisements (LSAs). By interpreting the information in these packets, routers are able to create maps of the entire network. Compare with distance-vector routing.

Linux

A Unix-like operating system kernel that was created by Linus Torvalds. Linux is distributed under an open-source license agreement, as are many of the applications and services that run on it.

LLC (logical link control) layer

A sublayer of the data-link layer of the OSI model. The LLC layer provides an interface for the network-layer protocols and the MAC sublayer.

LMHOSTS file

A text file that contains a list of NetBIOS hostname-to-IP address mappings used in TCP/IP name resolution.

logical addressing scheme

The addressing method used in providing manually assigned node addressing.

logical topology

The appearance of the network to the devices that use it, even if in physical terms the layout of the network is different.

See also [physical topology]

loop

A continuous circle that a packet takes through a series of nodes in a network until it eventually times out.

loopback plug

A device that is used for loopback testing.

loopback testing

A troubleshooting method in which the output and input wires are crossed or shorted in a manner that allows all outgoing data to be routed back into the card.

LTO (Linear Tape Open)

An open standard that allows both high storage capacity and fast data access in tape backup systems. LTO is implemented in two forms: Ultrium and Accelis.