Managing Serviceguard Nineteenth Edition, Reprinted June 2011

configuration, all subnets configured on that node, and identified as monitored subnets in the
package configuration file, must be available.)
Note that remote switching is supported only between LANs of the same type. For example, a
remote switchover between an Ethernet interface on one machine and an IPoIB interface on the
failover machine is not supported. The remote switching of relocatable IP addresses is shown in
Figure 14 and Figure 15.
Address Resolution Messages after Switching on the Same Subnet
When a relocatable IPv4 address is moved to a new interface, either locally or remotely, an ARP
message is broadcast to indicate the new mapping between IP address and link layer address.
An ARP message is sent for each IPv4 address that has been moved. All systems receiving the
broadcast should update the associated ARP cache entry to reflect the change. Currently, the ARP
messages are sent at the time the IP address is added to the new system. An ARP message is sent
in the form of an ARP request. The sender and receiver protocol address fields of the ARP request
message are both set to the same relocatable IP address. This ensures that nodes receiving the
message will not send replies.
Unlike IPv4, IPv6 addresses use NDP messages to determine the link-layer addresses of their
neighbors.
Monitoring LAN Interfaces and Detecting Failure: IP Level
In addition to monitoring network interfaces at the link level, Serviceguard can also monitor the IP
level, checking Layer 3 health and connectivity for both IPv4 and IPv6 subnets. This is done by the
IP Monitor, which is configurable: you can enable IP monitoring for any subnet configured into the
cluster, but you do not have to monitor any. You can configure IP monitoring for a subnet, or turn
off monitoring, while the cluster is running.
The IP Monitor:
• Detects when a network interface fails to send or receive IP messages, even though it is still
able to send and/or receive DLPI messages.
• 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 71)
• 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 even when the cluster configuration parameter
NETWORK_FAILURE_DETECTION is not set to INONLY_OR_INOUT
NOTE: This applies only to subnets for which the cluster configuration parameter
IP_MONITOR is set to ON. See “Cluster Configuration Parameters ” (page 105) for more
information.
◦ Errors that prevent packets from being received but do not affect the link-level health of
an interface
70 Understanding Serviceguard Software Components