D-Link DFL-1660 User Manual page 140

4.2.4. Host Monitoring for Route
Failover
The advantages of Host Monitoring are twofold:
• In a complex network topology it is more reliable to check accessibility to external hosts. Just
monitoring a link to a local switch may not indicate a problem in another part of the internal
network.
• Host monitoring can be used to help in setting the acceptable Quality of Service level of Internet
response times. Internet access may be functioning but it may be desirable to instigate route
failover if response latency times become unacceptable using the existing route.
Enabling Host Monitoring
As part of Route Properties Host Monitoring can be enabled and a single route can have multiple
hosts associated with it for monitoring. Multiple hosts can provide a higher certainty that any
network problem resides in the local network rather than because one remote host itself is down.
In association with Host Monitoring there are two numerical parameters for a route:
Grace Period
Minimum Number of Hosts
Available
Specifying Hosts
For each host specified for host monitoring there are a number of property parameters that should be
set:
• Method
The method by which the host is to be polled. This can be one of:
• ICMP - ICMP "Ping" polling. An IP address must be specified for this.
• TCP - A TCP connection is established to and then disconnected from the host. An IP
address must be specified for this.
• HTTP - A normal HTTP server request using a URL. A URL must be specified for this as
well as a text string which is the beginning (or complete) text of a valid response. If no text
is specified, any response from the server will be valid.
• IP Address
The IP address of the host when using the ICMP or TCP option.
• Port Number
The port number for polling when using the TCP option.
• Interval
The interval in milliseconds between polling attempts. The default setting is 10,000 and the
minimum value allowed is 100 ms.
This is the period of time after startup or after reconfiguration
of the NetDefend Firewall which NetDefendOS will wait
before starting Route Monitoring. This waiting period allows
time for all network links to initialize once the firewall comes
online.
This is the minimum number of hosts that must be considered
to be accessible before the route is deemed to have failed. The
criteria for host accessibility are described below.
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Chapter 4. Routing