ATM Address Resolution

Because an ATM network is non-broadcast, ARP broadcasts (as used by Ethernet or Token Ring) are not a suitable solution. Instead, a dedicated Address Resolution Protocol server (or ARP server) is used to provide IP-to-ATM address resolution. One of the stations in a LIS is designated as an ARP server (and the ARP server software is loaded on it). Stations that use the services of the ARP server are referred to as ARP clients. All IP stations within a LIS are ARP clients. Each ARP client is configured with the ATM address of the ARP server. When an ARP client starts up, it makes an ATM connection to the ARP server, and sends a packet to the server that contains the client's IP and ATM addresses. The ARP server builds a table of IP-address-to-ATM-address mappings. When a client has an IP packet to be sent to another client (whose IP address is known but whose ATM address is unknown), it first queries the ARP server for the ATM address of the desired client. When it receives a reply that contains the desired ATM address, the client establishes a direct ATM connection to the target client and sends IP packets for that client on this connection. The clients close any ATM connection, including the connection to the server, if the connections are inactive. All clients refresh their IP and ATM address information with the server periodically (the default is 15 minutes). An entry that is not refreshed after 20 minutes (by default) is purged by the server. The ATM ARP client and ARP server both support a number of adjustable registry parameters, which are listed in Appendix A.