C.2 Public Network Monitoring (PNM)

The PNM component has two primary functions:

• To monitor the status of configured adapters on a node and report general adapter or network failures.

• To fail over transparently to other backup adapters on a node when the primary adapter fails.

PNM is implemented as a daemon (pnmd) which periodically gathers network statistics on the set of public network interfaces in a node. If the results indicate any abnormalities, pnmd attempts to distinguish between the following three cases:

• The network is quiescent.

• The network is down.

• The network interface is down.

PNM then does a directed ping to a peer daemon on the same subnet. If there is no reply, PNM does a broadcast ping on the same subnet. PNM then places the results of its findings in the CCD and compares the local results with the results of the other nodes (which are also placed in the CCD). This comparison is used to determine whether the network is down or whether the network interface is faulty. If PNM detects that the network interface is faulty and backup adapters are configured, it performs the network adapter failover.

The results of PNM monitoring are used by various entities. The network adapter failover component of PNM uses the monitoring results to decide whether an adapter failover would be useful. For example, if the network is experiencing a failure, no adapter failover is performed. Fault monitors associated with SC HA data services and the API call hactl use the PNM facility to diagnose the cause of data service failures. The information returned by PNM is used to decide whether to migrate the data service, and to determine the location of the data service after migration.

The syslog messages written by the PNM facility on detection of adapter failures are read by the SC Manager, which translates the messages into graphic icons and displays them through the graphical user interface.

You also can run the PNM utilities on the command line to determine the status of network components. For more information, see the man pages pnmset(1M), pnmstat(1M), pnmptor(1M), pnmrtop(1M), and pnmd(1M).