Managing HP Serviceguard for Linux, Tenth Edition, September 2012

The IP Monitor:
• Detects when a network interface fails to send or receive IP messages, even though
it is still up at the link level.
• Handles the failure, failover, recovery, and failback.
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 76)
• 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 27).
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 79) and “Failure and Recovery Detection Times” (page 78).
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 103).
cmquerycl (1m) will detect gateways available for use as polling targets, as
shown in the example below.
76 Understanding Serviceguard Software Components