Managing Serviceguard Sixteenth Edition, March 2009

NOTE: This applies only to subnets for which the cluster configuration
parameter IP_MONITOR is set to ON. See “Cluster Configuration Parameters
” (page 138) for more information.
— Errors that prevent packets from being received but do not affect the link-level
health of an interface
IMPORTANT: You should configure the IP Monitor in a cross-subnet configuration,
because IP monitoring will detect some errors that link-level monitoring will not. See
also “Cross-Subnet Configurations” (page 41).
How the IP Monitor Works
Using Internet Control Message Protocol (ICMP) and ICMPv6, the IP Monitor sends
polling messages to target IP addresses and verifies that responses are received. When
four consecutive messages have not received a response, the IP Monitor considers the
subnet failed and marks the network interface down at the IP level. If there is no standby,
the subnet is marked down in the output of cmviewcl (1m); otherwise it is failed
over to the standby. The IP address is considered recovered when the IP Monitor has
successfully sent and received four consecutive messages.
The monitor can perform two types of polling:
• Peer polling.
In this case the IP Monitor sends ICMP ECHO messages from each IP address on
a subnet to all other IP addresses on the same subnet on other nodes in the cluster.
• Target polling.
In this case the IP Monitor sends ICMP ECHO messages from each IP address on
a subnet to an external IP address specified in the cluster configuration file; see
POLLING_TARGET under “Cluster Configuration Parameters ” (page 138).
cmquerycl (1m) will detect gateways available for use as polling targets, as
shown in the example below.
Target polling enables monitoring beyond the first level of switches, allowing you
to detect if the route is broken anywhere between the monitored IP address and
the target.
NOTE: In a cross-subnet configuration, nodes can configure peer interfaces on
nodes on the other routed subnet as polling targets.
HP recommends that you configure target polling if the subnet is not private to the
cluster.
The IP Monitor section of the cmquerycl output looks similar to this:
100 Understanding Serviceguard Software Components