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300-410 · Question #73

Refer to the exhibit. An IP SLA is configured to use the backup default route when the primary is down, but it is not working as desired. Which command fixes the issue? R1(config)# ip route 0.0.0.0…

The correct answer is D. R1(config)# ip route 0.0.0.0 0.0.0.0 1.1.1.1 track 1. To enable IP SLA to control the primary default route, the track object must be applied to the primary static route so that the route is dynamically withdrawn when the tracked object goes down.

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Question

Refer to the exhibit. An IP SLA is configured to use the backup default route when the primary is down, but it is not working as desired. Which command fixes the issue? R1(config)# ip route 0.0.0.0 0.0.0.0 1.1.1.1 R1(config)# ip route 0.0.0.0 0.0.0.0 2.2.2.2 10 R1(config)# ip sla 1 R1(config)# icmp-echo 1.1.1.1 source-interface FastEthernet0/0 R1(config)# ip sla schedule 1 life forever start-time now R1(config)# track 1 ip sla 1 reachability

Options

  • AR1(config)# ip route 0.0.0.0 0.0.0.0 2.2.2.2 10 track 1
  • BR1(config)# ip route 0.0.0.0 0.0.0.0 2.2.2.2
  • CR1(config)# ip sla track 1
  • DR1(config)# ip route 0.0.0.0 0.0.0.0 1.1.1.1 track 1

How the community answered

(55 responses)
  • A
    2% (1)
  • B
    5% (3)
  • C
    9% (5)
  • D
    84% (46)

Why each option

To enable IP SLA to control the primary default route, the `track` object must be applied to the primary static route so that the route is dynamically withdrawn when the tracked object goes down.

AR1(config)# ip route 0.0.0.0 0.0.0.0 2.2.2.2 10 track 1

Applying `track 1` to the backup route would cause the backup route to become active *only when* track 1 is up (i.e., when 1.1.1.1 is reachable), which is the opposite of the desired failover behavior.

BR1(config)# ip route 0.0.0.0 0.0.0.0 2.2.2.2

Removing the administrative distance from the backup route would make it active with an AD of 1, potentially interfering with or being load-balanced with the primary route, and it would not use IP SLA for failover.

CR1(config)# ip sla track 1

`ip sla track 1` is not a valid command to link an IP SLA operation to a track object or route; the correct command shown in the exhibit is `track 1 ip sla 1 reachability`.

DR1(config)# ip route 0.0.0.0 0.0.0.0 1.1.1.1 track 1Correct

The problem is that the primary default route `ip route 0.0.0.0 0.0.0.0 1.1.1.1` is always active regardless of the IP SLA status. By adding `track 1` to this route, the route will only be installed in the routing table when track object 1 (which monitors IP SLA 1's reachability to 1.1.1.1) is in an 'up' state. When 1.1.1.1 becomes unreachable, track 1 goes 'down', the primary route is removed, and the backup default route `ip route 0.0.0.0 0.0.0.0 2.2.2.2 10` (with its higher AD) becomes active.

Concept tested: IP SLA and static route tracking

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/reference/iap_r1.html#wp1026601

Topics

#IP SLA#Route Tracking#Static Routes#Default Route Failover

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