Managing Serviceguard Eighteenth Edition, September 2010

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 3-5 and Figure 3-6.
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 99)
• 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
98 Understanding Serviceguard Software Components