When MCAC enabled interfaces reside on a LAG, SR OS allows operators to change MCAC behavior when the number of active ports in a LAG changes. Both MCAC policy bundle and MCAC interface allows operators to define multiple MCAC levels per LAG based on the number of active ports in the LAG. For each level, operators can configure corresponding BW limits.
When MCAC LAG constraints are enabled, the level to use is selected automatically based on the configuration and a currently active number of LAG ports. In a case of the available bandwidth reduction (for example, a LAG link failure causes change to a level with smaller BW configured), MCAC attempts first to fit all mandatory channels (in an arbitrary order). If there is no sufficient capacity to carry all mandatory channels in the degraded mode, some channels are dropped and all optional channels are dropped. If after evaluation of mandatory channels, there remains available bandwidth, then all optional channels are re-evaluated (in an arbitrary order). Channel re-evaluation employs the above-described MCAC algorithm applied at the interface and bundle levels that use the constraints for the degraded mode of operation.