Users Guide

Track an IPv4/IPv6 Route
You can create an object that tracks the reachability or metric of an IPv4 or IPv6 route.
You specify the route to be tracked by its address and prex-length values. Optionally, for an IPv4 route, you can enter a VRF
instance name if the route is part of a VPN routing and forwarding (VRF) table. The next-hop address is not part of the denition of
a tracked IPv4/IPv6 route.
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.
Displaying Tracked Objects
To display the currently congured objects used to track Layer 2 and Layer 3 interfaces, and IPv4 and IPv6 routes, use the following
show commands.
To display the conguration and status of currently tracked Layer 2 or Layer 3 interfaces, IPv4 or IPv6 routes, use the show track
command. You can also display the currently congured per-protocol resolution values used to scale route metrics when tracking
metric thresholds.
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Object Tracking