Multihomed Hosts

The term multihomed host describes a host that is on more than one public network. Such a host has multiple host names and IP addresses; it has one host name/IP address pair for each network. Sun Cluster is designed to permit a host to appear on any number of networks, including just one (the non-multihomed case). Just as the physical host name has multiple host name/IP address pairs, each logical host has multiple host name/IP address pairs, one for each public network. By convention, one of the host names in the set of pairs is the same name as that of the logical host itself. When Sun Cluster moves a logical host from one physical host to another, the complete set of host name/IP address pairs for that logical host is moved.

For each Sun Cluster logical host, the set of host name/IP address pairs is part of the Sun Cluster configuration data and is specified by the system administrator when Sun Cluster is first installed and configured. The Sun Cluster Data Service API contains facilities for querying the set of pairs, specifically, the names_on_subnets field described in the hads(3HA) and haget(1M) man pages.

Most off-the-shelf data service daemons that have been written for Solaris already handle multihomed hosts properly. Many data services do all their network communication by binding to the Solaris wildcard address INADDR_ANY. This automatically causes them to handle all the IP addresses for all the network interfaces. INADDR_ANY effectively binds to all IP addresses currently configured on the machine. A data service daemon that uses INADDR_ANY generally does not have to be changed to handle the Sun Cluster logical host's IP addresses.