Public Network Adapters and IP Network Multipathing

Clients make data requests to the cluster through the public network. Each cluster node is connected to at least one public network through a pair of public network adapters.

Solaris Internet Protocol (IP) Network Multipathing software on Sun Cluster provides the basic mechanism for monitoring public network adapters and failing over IP addresses from one adapter to another when a fault is detected. Each cluster node has its own IP Network Multipathing configuration, which can be different from that on other cluster nodes.

Public network adapters are organized into IP multipathing groups (multipathing groups). Each multipathing group has one or more public network adapters. Each adapter in a multipathing group can be active, or you can configure standby interfaces that are inactive unless there is a failover. The in.mpathd multipathing daemon uses a test IP address to detect failures and repairs. If a fault is detected on one of the adapters by the multipathing daemon, a failover occurs. All network access fails over from the faulted adapter to another functional adapter in the multipathing group, thereby maintaining public network connectivity for the node. If a standby interface was configured, the daemon chooses the standby interface. Otherwise, in.mpathd chooses the interface with the least number of IP addresses. Because the failover happens at the adapter interface level, higher-level connections such as TCP are not affected, except for a brief transient delay during the failover. When the failover of IP addresses completes successfully, gratuitous ARP broadcasts are sent. The connectivity to remote clients is therefore maintained.

Because of the congestion recovery characteristics of TCP, TCP endpoints can suffer further delay after a successful failover as some segments could be lost during the failover, activating the congestion control mechanism in TCP.

Multipathing groups provide the building blocks for logical hostname and shared address resources. You can also create multipathing groups independently of logical hostname and shared address resources to monitor public network connectivity of cluster nodes. The same multipathing group on a node can host any number of logical hostname or shared address resources. For more information on logical hostname and shared address resources, see the Sun Cluster Data Services Planning and Administration Guide for Solaris OS.

The design of the IP Network Multipathing mechanism is meant to detect and mask adapter failures. The design is not intended to recover from an administrator using ifconfig(1M) to remove one of the logical (or shared) IP addresses. The Sun Cluster software views the logical and shared IP addresses as resources managed by the RGM. The correct way for an administrator to add or remove an IP address is to use scrgadm(1M) to modify the resource group containing the resource.

For more information about the Solaris implementation of IP Network Multipathing, see the appropriate documentation for the Solaris operating environment installed on your cluster.