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## 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 Oracle Solaris 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 node has its own IP network multipathing configuration, which can be different from the configuration on other nodes.

Public network adapters are organized into IP multipathing groups. Each multipathing group has one or more public network adapters. Each adapter in a multipathing group can be active. Alternatively, you can configure standby interfaces that are inactive unless a failover occurs.

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. Therefore, the daemon maintains public network connectivity for the node. If you configured a standby interface, the daemon chooses the standby interface. Otherwise, the daemon chooses the interface with the least number of IP addresses. Because the failover occurs 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, ARP broadcasts are sent. Therefore, the daemon maintains connectivity to remote clients.

Note - Because of the congestion recovery characteristics of TCP, TCP endpoints can experience further delay after a successful failover. Some segments might have been lost during the failover, activating the congestion control mechanism in TCP.

Multipathing groups provide the building blocks for logical host name and shared address resources. The same multipathing group on a node can host any number of logical host name or shared address resources. For more information about logical host name and shared address resources, see the Oracle Solaris Cluster Data Services Planning and Administration Guide.

Note - 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's use of `ipadm` to remove one of the logical (or shared) IP addresses. The Oracle Solaris Cluster software views the logical and shared IP addresses as resources that are managed by the RGM. The correct way for an administrator to add or to remove an IP address is to use `clresource` and `clresourcegroup` to modify the resource group that contains the resource.

For more information about the Oracle Solaris implementation of IP Network Multipathing, see Chapter 6, Administering IPMP (Tasks), in Managing Oracle Solaris 11.1 Network Performance.

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