Cluster-To-Lan Communication - Compaq ProLiant 1600 Administrator's Manual

Designing the Compaq ProLiant Clusters HA/F100 and HA/F200 2-15
Because the purpose of the redundant interconnect is to increase the
availability of the cluster, it is important to monitor the status of your
redundant NICs. Compaq Insight Manager and Compaq Insight Manager XE
simplify management of the interconnect by monitoring the state of the
interconnect card. You can view status information and alert conditions for all
cards in each node. If a failover event occurs due to a disruption in the
heartbeat, you can use the Compaq Insight Manager tools to determine where
the disruption originated.

Cluster-to-LAN Communication

Each cluster node must have at least one NIC that connects to the LAN.
Through this connection, network clients can access applications and data on
the cluster. If the LAN NIC fails in one of the nodes, any clients connected
directly to the cluster node by means of the computer name, cluster node
IP address, or MAC address of the NIC no longer have access to their
applications. Clients connected to a virtual server on the cluster (via the
IP address or network name of a cluster group) reconnect to the cluster
through the surviving cluster node.
Failure of a LAN NIC in a cluster node may have serious repercussions.
If your cluster is configured with a dedicated interconnect and a single
LAN NIC, the failure of a LAN NIC will prevent network clients from
accessing cluster groups running on that node. If the interconnect path is not
disrupted, it is possible that a failover will not occur. The applications will
continue to run on the node with the failed NIC; however, clients will be
unable to access them.
Install redundant NICs and use the Compaq Redundant NIC Utility to reduce
the possibility of LAN NIC failure. When your cluster nodes are configured
with the utility, the redundant NIC automatically takes over operation if the
primary NIC fails. Clients maintain their connection with their primary node
and, without disruption, continue to have access to their applications.
Compaq offers a dual-port NIC that can utilize the Compaq Redundant NIC
Utility. This also reduces the possibility of the failure scenario described
above. However, if the entire NIC or the node slot into which the NIC is
placed fails, the same failure scenario will occur.
Compaq Insight Manager and Compaq Insight Manager XE monitor the health
of any network cards used for the LAN. If any of the cards experience a fault,
the Compaq Insight Manager tools mark the card as "Offline" and change its
condition to the appropriate status.