Adaptive Bandwidth Detection

This feature is applicable to networks with VSAT, LOS, Microwave, 3G/4G/LTE WAN Links, for which the available bandwidth varies based on weather and atmosphere conditions, location, and line of site obstructions. It allows the SD-WAN appliances to adjust the bandwidth rate on the WAN Link dynamically based on a defined bandwidth range (minimum and maximum WAN link rate) to use the maximum amount of available bandwidth without marking the paths BAD.

  • Greater bandwidth reliability (Over VSAT, Microwave, 3G/4G, and LTE)
  • Greater predictability of adaptive bandwidth over user configured settings

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The adaptive bandwidth feature works on loss detection. When the appliance starts the bandwidth increases for a virtual path to the maximum or until loss occurs. When 25% of the configured loss threshold is detected the bandwidth is reduced to the last known good rate. Periodically, the bandwidth increases in smaller increments. Again, when 25% of the configured loss threshold is detected the bandwidth is reduced to the last known good rate. If the loss threshold is triggered spontaneously, bandwidth is reduced aggressively until it is below the threshold.

The MTU first starts with the MTU configured for the WAN Link. It sends packet of a specific size with the DF bit set (as with all UDP packets). Retry is attempted up to three times. If the far-end receives the packet fragmented, it tries to infer the MTU. If the source receives an ICMP TOO BIG message, then it tries to infer the MTU. If the packets are never detected at the far end, it is considered test failed. Then lower the MTU and try again. This is attempted until success. The minimum value allowed is 576 bytes, which is the minimum allowed MTU allowed for IPv4 internet connectivity.

On each 10 minute interval, the process is repeated, however, it is started from the last learned MTU and initially increasing the packet size to see if the MTU has increased.

Note: Like any PMTU discovery, high loss in the network can cause false negatives causing us to erroneously detect lower MTU values. This is the reason there is a 10 minute retry. The recommendation is to enable MTU discovery to learn the network and once the deployment is stable convert the learned values to static values on the WAN links and disable detection to prevent MTU learning causing instability on lossy links.

To enable adaptive bandwidth detection:

This feature needs Bad loss sensitivity option to be enabled (default/custom) as a prerequisite. You can enable it under Global > Autopath Groups > Autopath Group Name > Bad Loss Sensitive.

  1. Enable Adaptive Bandwidth Detection under Global > Autopath Groups > **Autopath Group Name >Bad Loss Sensitive.

  2. Navigate to Configuration Editor > Sites > [Site Name] > WAN Links > [WAN Link Name] > Settings > Advanced Settings. localized image

  3. Check the Adaptive Bandwidth Detection box and enter a value in the Minimum Acceptable Bandwidth field.

  4. View the Usage and Permitted Rates table by navigating to Monitor > Statistics > WAN Link Usage > Usage and Permitted Rates.

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Adaptive Bandwidth Detection