D-Link DFL-260E User Manual for DFL-260E - Page 177
Host Monitoring for Route Failover, Gratuitous ARP Generation, Overview
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4.2.4. Host Monitoring for Route Failover Chapter 4. Routing change in the destination interface. Clearly, this is undesirable. To overcome this issue, potential destination interfaces should be grouped together into an Interface Group and the Security/Transport Equivalent flag should be enabled for the Group. The Interface Group is then used as the Destination Interface when setting policies. For more information on groups, see Section 3.4.6, "Interface Groups". Gratuitous ARP Generation By default NetDefendOS generates a gratuitous ARP request when a route failover occurs. The reason for this is to notify surrounding systems that there has been a route change. This behavior can be controlled by the advanced setting Gratuitous ARP on Fail. 4.2.4. Host Monitoring for Route Failover Overview To provide a more flexible and configurable way to monitor the integrity of routes, NetDefendOS provides the additional capability to perform Host Monitoring. This feature means that one or more external host systems can be routinely polled to check that a particular route is available. 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 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. Minimum Number of Hosts Available 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. Specifying Hosts For each host specified for host monitoring there are a number of property parameters that should be set: • Method 177