OER Variance to solve Policy Conflicts

When you configure a policy for OER you can choose what metrics are most important to you (packet loss, delay, jitter, etc.). For example, you can configure a policy that will choose an exit path based on the following criteria:

  1. Lowest Delay
  2. Lowest Jitter
  3. Lowest Packet Loss

Now imagine we have two exit paths with the following metrics:

  1. Exit A:
    1. Delay is 80ms
    2. Jitter is 5ms
    3. Packet loss is 2000ppm
  2. Exit B
    1. Delay is 90ms
    2. Jitter is 3ms
    3. Packet loss is 1500ppm

If we select exit A based on the lowest delay only, then we don’t make the best choice since the jitter and packet loss of exit A is worse than exit B. By using the variance, we can ensure that other exit paths fall within the “acceptable” criteria for a certain metric. This allows us to choose an exit path based on more than one metric.

Now let’s say I configure a variance of 15% for the delay. Exit path A has a delay of 80 ms. All exit paths that fall within 80 ms + 15% will be considered equal regarding the delay. 80ms + 15% = 92 ms. The delay for exit B (90 ms) is lower than 92 ms, so exit A and B are seen as “equal” when it comes to delay. This means we will have to look at the second metric (jitter).

Does this make sense? Let’s take a look at an actual policy with three exit paths:

  • Exit A:
    • Delay 100 ms
    • Jitter 5ms
    • Packet loss 2000ppm
  • Exit B:
    • Delay 150 ms
    • Jitter 6ms
    • Packet loss 1900ppm
  • Exit C:
    • Delay 110 m
    • Jitter 3ms
    • Packet loss 1900ppm
MC#show run | sec oer-map
oer-map VARIANCE 10
 match traffic-class prefix-list MYPREFIXES
 set resolve delay priority 1 variance 20
 set resolve loss priority 2 variance 10
 set resolve jitter priority 3 variance 15

Let me describe the policy above:

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