Binding to INADDR_ANY Versus Binding to Specific IP Addresses

Even in the non-multihomed case, the Sun Cluster logical host concept allows the machine to have more than one IP address. It has one for its own physical host and one additional IP address for each logical host it currently masters. When a machine becomes the master of a logical host, it dynamically acquires an additional IP address. When it gives up mastery of a logical host, it dynamically relinquishes an IP address.

Some data services cannot work properly using only INADDR_ANY. These data services must dynamically change the set of IP addresses to which they are bound as a logical host is mastered or unmastered. The starting and stopping methods provide the hooks for Sun Cluster to inform the data service that a logical host has appeared or disappeared. One strategy for such a data service to accomplish the rebinding is for its stop and start methods to kill and restart the data service's daemons.

During cluster reconfiguration, there is a relationship between the order in which data service methods are called and the time when the logical host's network addresses are configured by Sun Cluster. See the hareg(1M) man page for details about this relationship.

By the time the data service's stop method returns, the data service should have stopped using the logical host's IP addresses. Similarly, by the time the start_net method returns, the data service should have started to use the logical host's IP addresses. If the data service uses INADDR_ANY rather than binding to individual IP addresses, then there is no problem. If the data service's stop and start methods accomplish their work by killing and restarting the data service's daemons, then the data service stops and starts using the network addresses at the appropriate times.