D-Link NetDefendOS, User Manual

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4.2.3. Route Failover
Overview
NetDefend Firewalls are often deployed in mission-critical locations where availability and
connectivity is crucial. For example, an enterprise relying heavily on access to the Internet could
have operations severely disrupted if a single connection to the external Internet via a single
Internet Service Provider (ISP) fails.
It is therefore not unusual to have backup Internet connectivity using a secondary ISP. The
connections to the two service providers often use different routes to avoid a single point of
failure.
To allow for a situation with multiple ISPs, NetDefendOS provides a Route Failover capability so
that should one route fail, traffic can automatically failover to another, alternate route.
NetDefendOS implements route failover through the use of
Route Monitoring in which
NetDefendOS monitors the availability of routes and then switches traffic to an alternate route
should the primary, preferred route fail.
Figure 4.3. A Route Failover Scenario for ISP Access
Setting Up Route Failover
To set up route failover, Route Monitoring must be enabled and this is an option that is enabled
on a route by route basis. To enable route failover 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 this since it will usually have no route to failover to. When route monitoring is
enabled for a route, one of the following 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.
Chapter 4: Routing
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