LE ARP Cache

Each LEC client maintains a table of entries that establishes a relationship between destination MAC addresses and the ATM address to which data frames for the MAC address is sent. Each entry in the table is based on address information included in LE ARP Responses.

When the LEC receives a frame for transmission, and the destination MAC address is resident in the LE ARP cache, the client can forward the frame based on the ATM address mapping in the table. This eliminates the need to repeatedly generate an LE ARP request to determine the destination address. However, the MAC address may move due to a cabling change or a change in the spanning tree by a downstream bridge. This results in invalid mapping of MAC addresses to ATM addresses. To accommodate such changes, entries in the LE ARP cache are maintained for a limited period of time, thereby forcing generation of new LE ARP Requests and verification of MAC address-to-ATM address mappings.

Each entry in the cache is retained for a period of time equal to either the Aging Time or Forward Delay Time. Aging time is used to age entries in the cache under normal operation. Forward delay is used to age entries in the LE ARP cache when a topology change is in progress.

Refer to The ATM Forum Technical Committee's LAN Emulation Over ATM specification for a detailed discussion about the conditions under which the Aging Time and Forward Delay Time are used.