HP Serviceguard A.11.20- Managing Serviceguard Twentieth Edition, August 2011

NOTE: On Ethernet networks, Serviceguard supports local failover between network interfaces
configured with “Ethernet protocol” or between network interfaces configured with “SNAP
encapsulation within IEEE 802.3 protocol.” You cannot use both protocols on the same interface,
nor can you have a local failover between interfaces that are using different protocols.
Another example of local switching is shown in Figure 27. In this case a failure affecting segment
2 causes both nodes to switch to the LAN cards attached to segment 1.
Figure 27 Local Switching After Cable Failure
Local network switching will work with a cluster containing one or more nodes. You may wish to
design a single-node cluster in order to take advantage of this local network switching feature in
situations where you need only one node and do not wish to set up a more complex cluster.
Switching Back to Primary LAN Interfaces after Local Switching
If a primary interface fails, the IP address will be switched to a standby. You can use the
NETWORK_AUTO_FAILBACK parameter in the cluster configuration file to configure what
Serviceguard does if the primary interface is later restored.
• Default behavior: NETWORK_AUTO_FAILBACK = YES. Serviceguard will detect and log the
recovery of the interface, and will switch the IP address back to its primary interface.
In addition, when a node is halted, the cluster daemon (cmcld) will attempt to switch any
Serviceguard-configured IP addresses on standby interfaces back to their primary interfaces,
regardless of the link state of the primary interfaces. The intent of this switchback is to preserve
the original network configuration as it was before the cluster started. Switching back occurs
on the specified node if a cmhaltnode command is issued or on all nodes in the cluster if a
cmhaltcl command is issued.
• Configurable behavior: NETWORK_AUTO_FAILBACK = NO. Serviceguard will detect and log
the recovery of the interface, but will not switch the IP address back from the standby to the
primary interface.
You can tell Serviceguard to switch the IP address back to the primary interface by means of
the cmmodnet command:
cmmodnet -e <interface>
where <interface> is the primary interface.
72 Understanding Serviceguard Software Components