This section discusses an auto-bandwidth hierarchy configurable in the config>router>mpls>lsp context.
Adding auto-bandwidth at the LSP level starts the measurement of LSP bandwidth described in Measurement of LSP Bandwidth and allows auto-bandwidth adjustments to take place based on the triggers described in Periodic Automatic Bandwidth Adjustment.
When an LSP is first established, the bandwidth reserved along its primary path is controlled by the bandwidth parameter in the config>router>mpls>lsp>primary context, whether the LSP has auto-bandwidth enabled or not, while the bandwidth reserved along a secondary path is controlled by the bandwidth parameter in the config>router>mpls>lsp>secondary context. When auto-bandwidth is enabled and a trigger occurs, the system attempts to change the bandwidth of the LSP to a value between min-bandwidth and max-bandwidth, which are configurable values in the lsp>auto-bandwidthcontext. min-bandwidth is the minimum bandwidth that auto-bandwidth can signal for the LSP, and max-bandwidth is the maximum bandwidth that can be signaled. The user can set the min-bandwidth to the same value as the primary path bandwidth but the system does not enforce this restriction. The system allows:
no min-bandwidth to be configured. In this case, the implicit minimum is 0 Mb/s.
no max-bandwidth to be configured, as long as overflow-triggered auto-bandwidth is not configured. In this case, the implicit maximum is infinite (effectively 100 Gb/s).
the configured primary path bandwidth to be outside the range of min-bandwidth to max-bandwidth
auto-bandwidth parameters can be changed at any time on an operational LSP; in most cases, the changes have no immediate impact, but subsequent sections describe some exceptions
All of the auto-bandwidth adjustments discussed are performed using MBB procedures.
Auto bandwidth can be added to an operational LSP at any time (without the need to shut down the LSP or path), but no bandwidth change occurs until a future trigger event. Auto bandwidth may also be removed from an operational LSP at any time and this causes an immediate MBB bandwidth change to be attempted using the configured primary path bandwidth.
A change to the configured bandwidth of an auto-bandwidth LSP has no immediate effect. The change only occurs if the LSP/path goes down (because of a failure or an administrative action) and comes back up, or if auto-bandwidth is removed from the LSP. The operator can force an auto-bandwidth LSP to be resized immediately to an arbitrary bandwidth using the appropriate tools commands.