Network interface functions

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When a node is configured with multiple connections to a single network, the network interfaces serve different functions in PowerHA® SystemMirror®.

Service interface

A service interface is a network interface configured with a PowerHA SystemMirror service IP label. The service IP label is used by clients to access application programs. The service IP is only available when the corresponding resource group is online.

Persistent node IP label

A persistent node IP label is an IP alias that can be assigned to a specific node on a cluster network. A persistent node IP label always stays on the same node (node-bound), and coexists on an NIC that already has a service or boot IP label defined. A persistent node IP label is does not require installing an additional physical NIC on that node, and is not part of any resource group.

Assigning a persistent node IP label provides a node-bound address that you can use for administrative purposes, because a connection to a persistent node IP label always goes to a specific node in the cluster. You can have one persistent node IP label per network per node.

As one of the best practices for PowerHA SystemMirror, you must configure a persistent IP label for each cluster node. This is useful, for instance, if you must access a particular node in a PowerHA SystemMirror cluster for purposes of running reports or for diagnostics. Having a persistent IP label configured has the advantage that PowerHA SystemMirror can access the persistent IP label on the node despite individual NIC failures, assuming that there are spare NICs on the network.

After a persistent node IP label is configured on a specified network node, it becomes available at boot time and remains configured even if PowerHA SystemMirror is shut down on that node.

You can create persistent node IP labels on Ethernet networks.

The following list describes how PowerHA SystemMirror responds to a failure when a persistent node IP label is configured:

  • If a NIC that has a service IP label configured fails and there is also a persistent label defined on this NIC, the persistent label falls over to the same boot interface to which the service IP label falls over.
  • If all NICs on the cluster network on a specified node fail, the persistent node IP label becomes unavailable. A persistent node IP label always remains on the same network and on the same node. It does not move between the nodes in the cluster.