Performance-Measurement (Interface Delay)
Use any XRv9000.
Configure delay measurements for Gi0/0/0/0 using the following settings:
10 probes should be sent equally spaced every 20 seconds. Measurement computations should be calculated based on these 10 probes.
The router should periodically flood delay values into the IGP every 4 computations if the min delay changes by 5% or 500us. However, after any single computation if delay changes by 15% or 1ms, this should be immediately flooded.
Answer
Explanation
Performance-measurement allows the router to use TWAMP-light to measure delay on a link. This can be flooded into the IGP and used in SR-TE policies that optimize delay, and these statistics can be streamed to a collector using MDT.
By default the router will use two-way mode. This does not require clock sync, because only like values are compared against each other. (Two-way delay = T4-T1 - (T3-T2)). The router divides the result by two to produce a one-way delay value.
You can also use one-way mode, but this requires clock sync, typically using PTP. In this mode, T3 and T4 are not used. The delay is T2-T1.
The default values for performance-measurement interface delay are as follows:
A probe is sent every 3 seconds
The delay values are calculated every 30 seconds (10 probes)
The delay values are evaluated for advertisement into the IGP every 120 seconds. The value must differ by 10 percent and 1msec to be advertised.
Accelerated advertisement is disabled
Typically the default intervals and values for performance-measurement work well, but it is important to know how to change these if needed.
The values can be changed by using a delay-profile and applying it to the interface. You can also use the default profile, but I used a named profile in this lab for demonstration.
The probe intervals define how often to send a probe and how often to perform the delay calculations. In this lab we send 10 probes every 20 seconds, so the probe is sent every 2 seconds, and the computation is performed every 20 seconds.
Next we define how often the values can be flooded into the IGP. We set an interval of 80 seconds (4x 20seconds) and set the minimum change to 500us and 5%. This means that the measured value must differ by 5% and 500us of the current value advertised into the IGP to flood the change into the IGP.
Additionally, we define the accelerated timers. By default this is disabled. When enabled, if the value exceeds the threshold from the previous measurement, the change can be immediately flooded into the IGP. In our lab this means that every 20 seconds, the value are compared. If the current value differs from the current IGP value by 15% and 1ms, the change is immediately flooded instead of waiting for the 80 second advertisement interval.
Finally, this profile is applied to Gi0/0/0/0:
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