Link Monitoring And Ha - D-Link NetDefendOS User Manual

Chapter 11: High Availability

11.6. Link Monitoring and HA

Redundant Network Paths
When using an HA configuration, it can be important to use redundant paths to vital resources
such as the Internet. The paths through the network from the master device in an HA
configuration may fail in which case it may be desirable to have this failure trigger a failover to
the slave unit which has a different path to the resource.
Monitoring Paths
Monitoring the availability of specific network paths can be done with the NetDefendOS Link
Monitor. The Link Monitor allows the administrator to specify particular hosts whose reachability
is monitored using ICMP "Ping" requests and therefore link status. If these hosts become
unreachable then the link is considered failed and a failover to a slave can be initiated. Provided
that the slave is using a different network link and also monitoring the reachability of different
hosts, traffic can continue to flow.
Using the Shared IP Address
When this property of the Link Monitor object is enabled, it allows the link monitor pings to be
sent from the shared IP address instead of sending using the individual IPs of each unit. This is
useful if public IPv4 addresses are not available for the sending interface.
Further Link Monitor Reading
Using link monitoring is described further in Section 2.4.2, "The Link Monitor".
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