Amer Networks E5Web GUI - Manual (Page 264)

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.
Host Monitoring The first two options check the accessibility of components local
to the Clavister Security Gateway. An alternative is to monitor
the accessibility of one or more nominated remote hosts. These
hosts might have known high availability and polling them can
indicate if traffic from the local Clavister Security Gateway is
reaching them. Host monitoring also provides a way to measure
the network delays in reaching remote hosts and to initiate
failover
to an alternate route if delays exceed
administrator-specified thresholds.
Automatically Added Routes Need Redefining
It is important to note that the route monitoring cannot be enabled on automatically added
routes. For example, the routes that cOS Core creates at initial startup for physical interfaces are
automatically added routes. The reason why monitoring cannot be enabled for these routes is
because automatically created routes have a special status in an cOS Core configuration and are
treated differently.
If route monitoring is required on an automatically created route, the route should first be
deleted and then recreated manually as a new route. Monitoring can then be enabled on the
new route.
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, cOS Core 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 second failover route. The first two routes would have route monitoring enabled in the
routing table but the last one (with the highest metric) would not since it has no route to failover
to.
Failover Processing
Whenever monitoring determines that a route is not available, cOS Core will mark the route as
Chapter 4: Routing
264