LAN Emulation Servers

There are three types of LAN Emulation servers. Each type is briefly described in this section.

LAN Emulation Configuration Server

This server is first contacted by a host interface when the host is brought up on the emulated LAN. Its address is generally a well-known address specified by the LAN Emulation standard that is coded into the host software; thus establishing this connection requires no input from you. When contacted by a host wishing to join its emulated LAN, the LECS replies with configuration parameters for the emulated LAN, as well as the address of the LES.

LAN Emulation Server

The second step in joining an emulated LAN is to make a connection to the LAN Emulation Server. After receiving the LES address from the LECS, a host will establish a connection to the LES. The LES may add the host to a point-to-multipoint call that is maintained by the LES with connections to every host in the emulated LAN. This point-to-multipoint connection, if created by the LES, is used to send control information to each host on the emulated LAN.

The LES acts as the ATM ARP server. Since IP and ARP work with MAC addresses, an additional address resolution step is required to convert a MAC address to the corresponding ATM address, which is used to make a connection to the target host; this resolution step is provided by the LES.

Broadcast and Unknown Address Server

The final step in joining an emulated LAN is to make a connection to the BUS. The ATM address of the BUS is obtained by sending a LAN Emulation ARP request to the LES for the broadcast address. Once established, this connection is used to send broadcast messages to the BUS, which will add the client to a point-to-multipoint call including all hosts on the emulated LAN. Thus when a broadcast message (such as an IP ARP request) is received by the LAN Emulation host from its upper layers, it sends that message to the BUS, which forwards it to all hosts in the emulated LAN. Just as in the case of ethernet, the correct host responds to the sender, and thus the IP address is resolved to a MAC address.