The strict option tells an edge router to simply drop the data traffic if no tunnel meets the SLA class. This is the only option in an App-route policy that is not a loose matching.

Let’s reconfigure the app-route policy as shown in the output below and see how it behaves.

policy
app-route-policy APP-ROUTE-POLICY
 vpn-list VOIP
  sequence 11
   match
    dscp 46
   !
   action
    sla-class VOIP-SLA strict preferred-color mpls
!

Many engineers ask the question: Why would anyone want to drop data traffic just because WAN quality goes above a threshold?

Let’s look at a real-world example where latency rises above the SLA threshold. In that case, you might prefer to drop the traffic, because some real-time systems depend on data arriving on time, not just arriving eventually. For example, radar and air-traffic surveillance systems calculate an aircraft’s position using time-sensitive measurements. A plane can fly above 1,000 km/h, which is about 300 meters per second. If position updates arrive late, the reported coordinates can be hundreds of meters behind where the aircraft really is. In that moment, the data is not just less useful. It can become misleading.