Managing HP Serviceguard A.11.20.20 for Linux, May 2013

• 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.
3.5.7.1 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 67)
• 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).
3.5.7.2 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 69) and “Failure and Recovery Detection
Times” (page 68).
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 91). 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 each 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:
…
Route Connectivity (no probing was performed):
IPv4:
1 16.89.143.192
3.5 How the Network Manager Works 67