The Cisco implementation of LANE makes an ATM interface look like one or more Ethernet interfaces.
LANE is an ATM service defined by the ATM Forum specification LAN Emulation over ATM, ATM_FORUM 94-0035. This service emulates the following LAN-specific characteristics:
- Connectionless services
- Multicast services
- LAN MAC driver services
LANE service provides connectivity between ATM-attached devices and connectivity with LAN-attached devices. This includes connectivity between ATM-attached stations and LAN-attached stations and also connectivity between LAN-attached stations across an ATM network.
Because LANE connectivity is defined at the MAC layer, upper protocol-layer functions of LAN applications can continue unchanged when the devices join emulated LANs (ELANs). This feature protects corporate investments in legacy LAN applications.
An ATM network can support multiple independent ELAN networks. Membership of an end system in any of the ELANs is independent of the physical location of the end system. This characteristic enables easy hardware moves and location changes. In addition, the end systems can also move easily from one ELAN to another, whether or not the hardware moves.
LANE in an ATM environment provides routing between ELANs for supported routing protocols and high-speed, scalable switching of local traffic.
The ATM LANE system has three servers that are single points of failure. These are the LANE Configuration Server (LECS), the ELAN server (LES), and the broadcast and unknown server (BUS). Beginning with Cisco IOS Release 11.2, LANE fault tolerance or Simple LANE Service Replication on the ELAN provides backup servers to prevent problems if these servers fail.
The fault tolerance mechanism that eliminates these single points of failure is described in the "Configuring LAN Emulation" chapter. Although this scheme is proprietary, no new protocol additions have been made to the LANE subsystems.
Any number of ELANs can be set up in an ATM switch cloud. A router can participate in any number of these ELANs.
LANE is defined on a LAN client/server model. The following components are implemented:
- LANE client--A LANE client emulates a LAN interface to higher layer protocols and applications. It forwards data to other LANE components and performs LANE address resolution functions.
Each LANE client is a member of only one ELAN. However, a router can include LANE clients for multiple ELANs: one LANE client for each ELAN of which it is a member.
If a router has clients for multiple ELANs, the Cisco IOS software can route traffic between the ELANs.
- LES--The LES for an ELAN is the control center. It provides joining, address resolution, and address registration services to the LANE clients in that ELAN. Clients can register destination unicast and multicast MAC addresses with the LES. The LES also handles LANE ARP (LE ARP) requests and responses.
The Cisco implementation has a limit of one LES per ELAN.
- LANE BUS--The LANE BUS sequences and distributes multicast and broadcast packets and handles unicast flooding.
In this release, the LES and the LANE BUS are combined and located in the same Cisco 7000 family or Cisco 4500 series router; one combined LECS and BUS is required per ELAN.
- LECS--The LECS contains the database that determines which ELAN a device belongs to (each configuration server can have a different named database). Each LANE client consults the LECS just once, when it joins an ELAN, to determine which ELAN it should join. The LECS returns the ATM address of the LES for that ELAN.
One LECS is required per LANE ATM switch cloud.
The LECS's database can have the following four types of entries:
- ELAN name-ATM address of LES pairs
- LANE client MAC address-ELAN name pairs
- LANE client ATM template-ELAN name pairs
- Default ELAN name
ELAN names must be unique on an interface. If two interfaces participate in LANE, the second interface may be in a different switch cloud.