Track Layer 3 InterfacesYou can create an object that tracks the Layer 3 state (IPv4 or IPv6 routing status) of an interface.• The Layer 3 status of an interface is UP only if the Layer 2 status of the interface is UP and the interfacehas a valid IP address.• The Layer 3 status of an interface goes DOWN when its Layer 2 status goes down or the IP address isremoved from the routing table.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 or IPv6 address and prefix-length. Optionally specify a tracked route by avirtual routing and forwarding (VRF) instance name if the tracked route is part of a VRF. The next-hop addressis not part 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 an entryin the routing table. For example, when configured as a tracked route, 10.0.0.0/24 does not match therouting table entry 10.0.0.0/8. If no route-table entry has the exact address and prefix length, the trackedroute 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 is trackedin 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 a Metric ThresholdIf you configure a metric threshold to track a route, the UP/DOWN state of the tracked route is determined bythe 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 0 to255, where 0 is connected and 255 is inaccessible. The scaled metric value communicated to a client alwaysconsiders a lower value to have priority over a higher value. The resulting scaled value is compared againstthe 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 is UP.• 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 is 254;the default DOWN threshold is 255. The notification of a change in the state of a tracked object is sent whena 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 and calculatesthe scaled metric by dividing a route's cost by the resolution value set for the route type:Object Tracking 731
