Track IPv4 and IPv6 RoutesYou can create an object that tracks an IPv4 or IPv6 route entry in the routing table.Specify a tracked route by its IPv4/IPv6 address and prefix-length, and optionally, by a virtual routing andforwarding (VRF) instance name if the route to be tracked is part of a VRF. The next-hop address is notpart of the definition of the tracked object.A tracked route matches a route in the routing table only if the exact address and prefix length match anentry in the routing table. For example, when configured as a tracked route, 10.0.0.0/24 does not matchthe routing table entry 10.0.0.0/8. If no route-table entry has the exact address and prefix length, thetracked route is considered to be DOWN.In addition to the entry of a route in the routing table, you can configure how the status of a route istracked in either the following ways:• By the reachability of the route's next-hop router.• By comparing the UP or DOWN threshold for a route’s metric with current entries in the route table.Track Route ReachabilityIf you configure the reachability of an IP route entry as a tracked object, the UP/DOWN state of the routeis determined by the entry of the next-hop address in the ARP cache.A tracked route is considered to be reachable if there is an address resolution protocol (ARP) cache entryfor the route's next-hop address. If the next-hop address in the ARP cache ages out for a route trackedfor its reachability, an attempt is made to regenerate the ARP cache entry to see if the next-hop addressappears before considering the route DOWN.Track a Metric ThresholdIf you configure a metric threshold to track a route, the UP/DOWN state of the tracked route isdetermined by the current metric for the route entered in the routing table.To provide a common tracking interface for different clients, route metrics are scaled in the range from 0to 255, where 0 is connected and 255 is inaccessible. The scaled metric value communicated to a clientalways considers a lower value to have priority over a higher value. The resulting scaled value iscompared against the threshold values to determine the state of a tracked route as follows:• If the scaled metric for a route entry is less than or equal to the UP threshold, the state of a route isUP.• If the scaled metric for a route is greater than or equal to the DOWN threshold or the route is notentered in the routing table, the state of a route is DOWN.The UP and DOWN thresholds are user-configurable for each tracked route. The default UP threshold is254; the default DOWN threshold is 255. The notification of a change in the state of a tracked object issent when a metric value crosses a configured threshold.The tracking process uses a protocol-specific resolution value to convert the actual metric in the routingtable to a scaled metric in the range from 0 to 255. The resolution value is user-configurable andcalculates the scaled metric by dividing a route's cost by the resolution value set for the route type:• For intermediate system to intermediate system (ISIS), you can set the resolution in the range from 1to 1000, where the default is 10.540 Object Tracking
