Users Guide

Track IPv4 and IPv6 Routes
You 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
a virtual routing and forwarding (VRF) instance name if the tracked route is part of a VRF. The next-hop
address is 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
entry in the routing table. For example, when configured as a tracked route, 10.0.0.0/24 does not match
the routing table entry 10.0.0.0/8. If no route-table entry has the exact address and prefix length, the
tracked 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 is
tracked 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 a Metric Threshold
If you configure a metric threshold to track a route, the UP/DOWN state of the tracked route is
determined 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 0
to 255, where 0 is connected and 255 is inaccessible. The scaled metric value communicated to a client
always considers a lower value to have priority over a higher value. The resulting scaled value is
compared 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 is
UP.
• If the scaled metric for a route is greater than or equal to the DOWN threshold or the route is not
entered 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 when a metric value crosses a configured threshold.
The tracking process uses a protocol-specific resolution value to convert the actual metric in the routing
table to a scaled metric in the range from 0 to 255. The resolution value is user-configurable and
calculates 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 1
to 1000, where the default is 10.
• For OSPF, you can set the resolution in the range from 1 to 1592, where the default is 1.
• The resolution value used to map static routes is not configurable. By default, Dell Networking OS
assigns a metric of 0 to static routes.
• The resolution value used to map router information protocol (RIP) routes is not configurable. The RIP
hop-count is automatically multiplied by 16 to scale it; a RIP metric of 16 (unreachable) scales to 256,
which considers the route to be DOWN. For example, to configure object tracking for a RIP route to
be considered UP only if the RIP hop count is less than or equal to 4, you would configure the UP
threshold to be 64 (4 x 16) and the DOWN threshold to be 65.
Object Tracking
685