Address Resolution Scenario 2 Using LEARP to Resolve NSAP Addresses

Workstation A needs to contact Workstation B, and Workstation A already knows both its IP and MAC addresses. Once Workstation A's LEC receives a unicast frame, it must find Workstation B's LEC via its NSAP address so that a Data Direct VC can be built between the LECs. LE_ARP is used to resolve the NSAP address:

Step 1 Workstation A sends a frame to Workstation B's MAC address.

Workstation A's switch has an entry for the MAC address on its ATM module, pointing toward an ELAN.

Step 2 Workstation A's LEC does not know the NSAP address for

Workstation B's LEC. Therefore, Workstation A's LEC sends an LE_ARP request to the LES.

Step 3 The LES looks up Workstation B's MAC address in its MAC/

NSAP address table. If the LES finds the NSAP entry, it replies to Workstation A's LEC with the address.

Step 4 If the NSAP entry is not in the table, the LES forwards the

LE_ARP request on to all ELAN LECs over its multipoint control connection.

Step 5 The LEC where Workstation B is attached has the MAC address in its bridging table. Therefore, Workstation B's LEC sends an LE_ARP reply back to the LES with its NSAP address.

Step 6 Workstation A's LEC can now build a Data Direct VC to Workstation B's LEC for data transfer.

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