Layer 2 Forwarding Protocol. Protocol that supports the creation of secure virtual private dial-up networks over the Internet.
Communications transactions between the LAC and the LNS that support tunneling of a single PPP connection. There is a one-to-one relationship among the PPP connection, L2TP session, and L2TP call.
L2TP access concentrator. A node that acts as one side of an L2TP tunnel endpoint and is a peer to the L2TP network server (LNS). The LAC sits between an LNS and a remote system and forwards packets to and from each. Packets sent from the LAC
to the LNS require tunneling with the L2TP protocol as defined in this document. The connection from the LAC to the remote system is either local or a PPP link.
local-area network. High-speed, low-error data network covering a relatively small geographic area (up to a few thousand meters). LANs connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited area. LAN standards specify cabling and signaling at the physical and data link layers of the OSI model. Ethernet, FDDI, and Token Ring are widely used LAN technologies. Compare with MAN and WAN.
High-speed switch that forwards packets between data-link segments. Most LAN switches forward traffic based on MAC addresses. This variety of LAN switch is sometimes called a frame switch. LAN switches often are categorized according to the method they use to forward traffic: cut-through packet switching or store-and-forward packet switching. Multilayer switches are an intelligent subset of LAN switches. Compare with multilayer switch. See also cut-through packet switching and store and forward packet switching.
LAN emulation. Technology that allows an ATM network to function as a LAN backbone. The ATM network must provide multicast and broadcast support, address mapping (MAC-to-ATM), SVC management, and a usable packet format. LANE also
defines Ethernet and Token Ring ELANs.
Link Access Procedure, Balanced. Data link layer protocol in the X.25 protocol stack. LAPB is a bit-oriented protocol derived from HDLC. See also HDLC and X.25.
Link Access Procedure on the D channel. ISDN data link layer protocol for the D channel. LAPD was derived from the LAPB protocol and is designed primarily to satisfy the signaling requirements of ISDN basic access. Defined by ITU-T Recommendations Q.920 and Q.921.
1. Delay between the time a device requests access to a network and the time it is granted permission to transmit.
2. Delay between the time a device receives a frame and the time that frame is forwarded out the destination port.
Layer 2 Tunnel Protocol (L2TP)
An Internet Engineering Task Force (IETF) standards track protocol defined in RFC 2661 that provides tunneling of PPP. Based upon the best features of L2F and PPTP, L2TP provides an industry-wide interoperable method of implementing VPDN.
Layer 3 Switching
Emerging Layer 3 switching technology that integrates routing with switching to yield very high routing throughput rates in the millions-of-packets- per-second range. The movement to Layer 3 switching is designed to address the downsides of the current generation of Layer 2 switches, which functionally are equivalent to bridges. These downsides for a large, flat network include being subject to broadcast storms, spanning tree loops, and address limitations.
link control protocol. Protocol that establishes, configures, and tests data-link connections for use by PPP. See also PPP.
Lightweight Directory Access Protocol. Protocol that provides access for management and browser applications that provide read/write interactive access to the X.500 Directory.
label distribution protocol. A standard protocol between MPLS-enabled routers to negotiate the labels (addresses) used to forward packets.
Transmission line reserved by a communications carrier for the private use of a customer. A leased line is a type of dedicated line.
link-state routing algorithm
Routing algorithm in which each router broadcasts or multicasts information regarding the cost of reaching each of its neighbors to all nodes in the internetwork. Link state algorithms create a consistent view of the network and therefore are not prone to routing loops; however, they achieve this at the cost of relatively greater computational difficulty and more widespread traffic (compared with distance vector routing algorithms). Compare with distance vector routing algorithm.
Local Management Interface. Set of enhancements to the basic Frame Relay specification. LMI includes support for a keepalive mechanism, which verifies that data is flowing; a multicast mechanism, which provides the network server with its local DLCI and the multicast DLCI; global addressing, which gives DLCIs global rather than local significance in Frame Relay networks; and a status mechanism, which provides an on-going status report on the DLCIs known to the switch. Known as LMT in ANSI terminology.
L2TP network server. A node that acts as one side of an L2TP tunnel endpoint and is a peer to the L2TP access concentrator (LAC). The LNS is the logical termination point of a PPP session that is being tunneled from the remote system by the LAC.
Analogous to the Layer 2 Forwarding (L2F) home gateway (HGW).
In routing, the capability of a router to distribute traffic over all its network ports that are the same distance from the destination address. Good load-balancing algorithms use both line speed and reliability information. Load balancing increases the use of
network segments, thus increasing effective network bandwidth.
Line from the premises of a telephone subscriber to the telephone company CO.
Route where packets never reach their destination, but simply cycle repeatedly through a constant series of network nodes.
Test in which signals are sent and then directed back toward their source from some point along the communications path. Loopback tests often are used to test network interface usability.
link-state advertisement. Broadcast packet used by link-state protocols that contains information about neighbors and path costs. LSAs are used by the receiving routers to maintain their routing tables. Sometimes called an LSP.
label switched path tunnel. A configured connection between two routers that uses MPLS to carry the packets.
label switch router. The role of an LSR is to forward packets in an MPLS network by looking only at the fixed-length label. Also called P-Router.