D-Link 800 - DFL 800 - Security Appliance, User Manual

Page: 131 / 469

Figure 4.2. A Route Failover Scenario for ISP Access
Setting Up Route Failover
Route Monitoring should be enabled on a per-route basis. To enable the Route Failover feature in a
scenario with a preferred and a backup route, the preferred route will have Route Monitoring
enabled, however the backup route does not require it to be enabled since it will usually have no
route to failover to. For a route with Route Monitoring enabled, one of two Route Monitoring
methods must be chosen:
Interface Link Status NetDefendOS will monitor the link status of the interface
specified in the route. As long as the interface is up, the route is
diagnosed as healthy. This method is appropriate for monitoring
that the interface is physically attached and that the cabling is
working as expected. As any changes to the link status are
instantly noticed, this method provides the fastest response to
failure.
Gateway Monitoring If a specific gateway has been specified as the next hop for a
route, accessibility to that gateway can be monitored by sending
periodic ARP requests. As long as the gateway responds to these
requests, the route is considered to be functioning correctly.
Setting the Route Metric
When specifying routes, the administrator should manually set a route's Metric. The Metric is a
positive integer that indicates how preferred the route is as a means to reach its destination. When
two routes offer a means to reach the same destination, NetDefendOS will select the one with the
lowest Metric value for sending data (if two routes have the same Metric, the route found first in the
routing table will be chosen).
A primary, preferred route should have a lower Metric (for example "10"), and a secondary, failover
route should have a higher Metric value (for example "20").
Multiple Failover Routes
It is possible to specify more than one failover route. For instance, the primary route could have two
other routes as failover routes instead of just one. In this case the Metric should be different for each
of the three routes: "10" for the primary route, "20" for the first failover route and "30" for the
4.2.3. Route Failover Chapter 4. Routing
131