Users Guide

In order for an route’s reachability or metric to be tracked, the route must appear as an entry in the routing table. A tracked route is
considered to match an entry in the routing table only if the exact IPv4 or IPv6 address and prex length match an entry in the table. For
example, when congured as a tracked route, 10.0.0.0/24 does not match the routing table entry 10.0.0.0/8. Similarly, for an IPv6 address,
3333:100:200:300:400::/80 does not match routing table entry 3333:100:200:300::/64. If no route-table entry has the exact IPv4/IPv6
address and prex length, the tracked route is considered to be DOWN.
In addition to the entry of a route in the routing table, you can congure the UP/DOWN state of a tracked route to be determined in the
following ways:
• By the reachability of the route's next-hop router.
The UP/DOWN state of the route is 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 ARP cache entry for the route's next-hop address. If the next-hop address in the ARP cache ages out for
a route tracked for its reachability, an attempt is made to regenerate the ARP cache entry to see if the next-hop address appears
before considering the route DOWN.
• By comparing the threshold for a route’s metric with current entries in the route table.
The UP/DOWN state of the tracked route is determined by the threshold for the current value of the route metric in the routing table.
To provide a common tracking interface for dierent 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 congured 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-congurable for each tracked route. The default UP threshold is 254; the default DOWN
threshold is 255. The notication of a change in the state of a tracked object is sent when a metric value crosses a congured
threshold.
The tracking process uses a protocol-specic 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-congurable and calculates the scaled metric by dividing a route’s cost by the
resolution value set for the route type:
• For 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 congurable. By default, Dell Networking OS assigns a metric of 0 to static
routes.
• The resolution value used to map RIP routes is not congurable. The RIP hop-count is automatically multiplied by 16 to scale it. For
example, a RIP metric of 16 (unreachable) scales to 256, which considers a route to be DOWN.
Tracking Route Reachability
Use the following commands to congure object tracking on the reachability of an IPv4 or IPv6 route.
To remove object tracking, use the no track object-id command.
1 Congure object tracking on the reachability of an IPv4 or IPv6 route.
CONFIGURATION mode
track object-id {ip route ip-address/prefix-len | ipv6 route ipv6-address/prefix-len}
reachability [vrf vrf-name]
Valid object IDs are from 1 to 65535.
Enter an IPv4 address in dotted decimal format; valid IPv4 prex lengths are from / 0 to /32.
Enter an IPv6 address in X:X:X:X::X format; valid IPv6 prex lengths are from / 0 to /128.
Object Tracking
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