Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.112.0P1 - Page 601

Interface TenGigabitEthernet 7/11 ipv6 routing Description: Austin access point 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 prefix-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 definition 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 prefix length match an entry in the 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. 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 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 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 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 configured 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 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 RIP routes is not configurable. 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. Object Tracking 601