Secure Computing SG300 User Manual page 74

Advanced configurations
The supplied script is intended as a starting point for more advanced High Availability
configurations.
By default, a device is considered "up" and a candidate to become the master if it is
powered up and connected to the network segment. If you wish to have the device
become master only if some other service is available (say, an Internet connection), a
Test command may be added that checks for the availability of that resource and returns
0 if it is available.
/bin/highavaild may be configured any any interface, however if used on a non-LAN
interface, appropriate packet filter rules need to be configured to allow traffic via the
floating IP address (see the Packet Filtering section of the chapter entitled Firewall).
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Network Setup