The multipathing daemon in.mpathd detects interface failures and repairs. The daemon performs both link-based failure detection and probe-based failure detection if test addresses are configured for the underlying interfaces. Depending on the type of failure detection method that is employed, the daemon sets or clears the appropriate flags on the interface to indicate whether the interface failed or has been repaired. As an option, the daemon can also be configured to monitor the availability of all interfaces, including those that are not configured to belong to an IPMP group. For a description of failure detection, see Failure and Repair Detection in IPMP.
The in.mpathd daemon also controls the designation of active interfaces in the IPMP group. The daemon attempts to maintain the same number of active interfaces that was originally configured when the IPMP group was created. Thus in.mpathd activates or deactivates underlying interfaces as needed to be consistent with the administrator's configured policy. For more information about the manner by which the in.mpathd daemon manages activation of underlying interfaces, refer to How IPMP Works. For more information about the daemon, refer to the in.mpathd(1M) man page.
The IP kernel module manages outbound load-spreading by distributing the set of available IP data addresses in the group across the set of available underlying IP interfaces in the group. The module also performs source address selection to manage inbound load-spreading. Both roles of the IP module improve network traffic performance.
The IPMP configuration file /etc/default/mpathd is used to configure the daemon's behavior. For example, you can specify how the daemon performs probe-based failure detection by setting the time duration to probe a target to detect failure, or which interfaces to probe. You can also specify what the status of a failed interface should be after that interface is repaired. You also set the parameters in this file to specify whether the daemon should monitor all IP interfaces in the system, not only those that are configured to belong to IPMP groups. For procedures to modify the configuration file, refer to How to Configure the Behavior of the IPMP Daemon.
The ipmpstat utility provides different types of information about the status of IPMP as a whole. The tool also displays other specific information about the underlying IP interfaces for each group, as well as data and test addresses that have been configured for the group. For more information about the use of this command, see Monitoring IPMP Information and the ipmpstat(1M) man page.