Avaya M-ACCF/SF Address Resolution, If the destination MAC address is listed in the ARP Table

Chapter 1 Overview

Figure 1.7 LAN Emulation Clients and Ethernet Hosts

Hosts with

MAC Addresses

Avaya M770

Multifunction Switch

ATM Port with 16 LAN Emulation Clients (LECs) each with an ATM Address

ATM Access

Module

These clients represent (act as a proxy for) devices connected to the Ethernet ports.

Whenever an Ethernet device wants to communicate with another device over the ATM network, the LEC must first discover the ATM address of the LEC that is acting as a proxy for the destination MAC address. The LEC must do this for each unicast Ethernet frame sent. The process is known as Address Resolution.

Address Resolution

The process by which a LEC associates a LAN destination address with the ATM address of another LEC (or the BUS) is known as Address Resolution.

Each LEC keeps a LAN Emulation ARP Table (which should not to be confused with the IP ARP Table). The ARP Table lists the remote destination MAC addresses and the ATM address of the LEC through which each destination MAC address can be reached.

Prior to sending a frame with a known destination, the LEC checks the ARP Table to see if the destination MAC address of the frame is listed in the ARP Table. The action the LEC then takes depends on whether the MAC address is listed in the ARP Table:

•If the destination MAC address is listed in the ARP Table:

—and there is an ATM connection to that LEC, the frame is sent directly to that LEC.

—and an ATM connection has not already been set up, the LEC sets up an ATM connection.

•If the destination MAC address is not listed in the ARP Table:

the LEC sends the frame to the BUS. The BUS then sends the frame to all LECs on the Emulated LAN.

Sending a frame to every LEC is an inefficient use of resources, so the LEC also tries to locate the MAC address for future use.

To discover the correct address, the LEC uses a process called LAN Emulation Address Resolution Protocol (LE_ARP).

Avaya M770 M-ACCF/SF ATM Access Modules User’s Guide 13