Managing HP Serviceguard for Linux Ninth Edition, April 2009

Reasons To Use IP Monitoring
Beyond the capabilities already provided by link-level monitoring, IP monitoring can:
• Monitor network status beyond the first level of switches; see “How the IP Monitor
Works” (page 79)
• Detect and handle errors such as:
— IP packet corruption on the router or switch
— Link failure between switches and a first-level router
— Inbound failures
— 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 32).
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
the IP Monitor detects a failure, it marks the network interface down at the IP level, as
shown in the output of cmviewcl (1m); see “Reporting Link-Level and IP-Level
Failures” (page 82) and “Failure and Recovery Detection Times” (page 81).
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 100).
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.
How the Network Manager Works 79