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Configuring a Limit on Bandwidth Overflow Samples

The automatic bandwidth adjustment timer is a periodic timer which is triggered every adjust interval to determine whether any bandwidth adjustments are required on the LSP's active path. This interval is typically configured as a long period of time, usually hours. If, at the end of adjust interval, the change in bandwidth is above a certain adjust threshold, the LSP is resignaled with the new bandwidth.

During the automatic bandwidth adjustment interval, the router might receive a steady increase in traffic (increasing bandwidth utilization) on an LSP, potentially causing congestion or packet loss. To prevent this, you can define a second trigger to prematurely expire the automatic bandwidth adjustment timer before the end of the current adjustment interval.

Every statistics interval, the router samples the average bandwidth utilization of an LSP and if this has exceeded the current maximum average bandwidth utilization, the maximum average bandwidth utilization is updated.

During each sample period, the following conditions are also checked:

Is the current average bandwidth utilization above the current maximum average bandwidth utilization.
Has the change in maximum average bandwidth utilization exceeded the adjust threshold (bandwidth utilization has changed significantly).

If these conditions are true, it is considered to be one bandwidth overflow sample. Using the adjust-threshold-overflow-limit statement, you can define a limit on the number of bandwidth overflow samples such that when the limit is reached, the current automatic bandwidth adjustment timer is expired and a bandwidth adjustment is triggered. Once this adjustment is complete, the normal automatic bandwidth adjustment timer is reset to expire after the periodic adjustment interval.

To specify a limit on the number of bandwidth overflow samples before triggering an automatic bandwidth allocation adjustment, configure the adjust-threshold-overflow-limit statement:




adjust-threshold-overflow-limit number;

This statement can be configured at the following hierarchy levels:

[edit protocols mpls label-switched-path lsp-name auto-bandwidth]
[edit logical-systems logical-system-name protocols mpls label-switched-path lsp-name auto-bandwidth]

You must also configure the adjust-threshold and maximum-bandwidth statements whenever you configure the adjust-threshold-overflow-limit statement:

You must configure a nonzero value for the adjust-threshold statement if you configure the adjust-threshold-overflow-limit statement. Any bandwidth increase below the value configured for the adjust-threshold statement does not constitute an overflow condition.
To prevent unlimited increases in LSP bandwidth (to limit overflow beyond a certain bandwidth), you must also configure the maximum-bandwidth statement when you configure the adjust-threshold-overflow-limit statement.

Failure to configure either of these statements when you configure the adjust-threshold-overflow-limit statement results in a commit error.

The following describes the other aspects of the adjust-threshold-overflow-limit statement:

It only applies to bandwidth overflows. If the bandwidth is decreasing, the normal automatic bandwidth adjustment interval is used.
It does not affect manually triggered automatic bandwidth adjustment.
It applies to single class DiffServ-TE LSPs.
Because the adjust-threshold-overflow-limit statement can trigger a bandwidth adjustment, it cannot be enabled at the same time as the monitor-bandwidth statement (for information about that statement, see Configuring Passive Bandwidth Utilization Monitoring).
You cannot configure automatic bandwidth adjustments to occur more often than every 300 seconds. The adjust-threshold-overflow-limit statement is subject to the same minimum value with regard to the minimum frequency of adjustment allowed. Overflow condition based adjustments can occur no sooner than 300 seconds from the start of the overflow condition. Therefore it is required that:
sample interval x adjust-threshold-overflow-limit >= 300s

These values are checked during the commit operation. An error is returned if the value is less than 300 seconds.
If you change the value of the adjust-threshold-overflow-limit statement on a working router, you can expect the following behavior:
- If you increase the current value of the adjust-threshold-overflow-limit statement, the old value is replaced with the new one.
- If you decrease the current value of the adjust-threshold-overflow-limit statement and the current bandwidth overflow count is less than the new value, the old value is replaced with the new one.
- If you decrease the current value of the adjust-threshold-overflow-limit statement and the current bandwidth overflow count is greater than the new value, the adjustment timer is immediately expired and a bandwidth adjustment is initiated.

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