Classic IOS uses max
value (shape) and min value (bandwidth) to define each scheduler node behavior
when traffic congestion happens, or 2 parameter scheduler.
ASR 1000 utilize a
different 3-parameter scheduler: max value (shape), min value (bandwidth) and
excess value (bandwidth remaining) which is to adjust sharing of excess
bandwidth. In a 2-parameter scheduler, the excess bandwidth are shared by the
classes proportionally (same as the bandwidth ratio for each class); But in a
3-parameter scheduler, the excess bandwidth are shared equally by default after
satisfying minimum bandwidth requirements, but it can be tuned when using
‘bandwidth remaining’ command. ISR 4000 platforms share the same design.
In Classic IOS, it
is permitted to configure bandwidth at the leaf and intermediate nodes of a
hierarchy. In IOS XE, bandwidth (bandwidth rate , or bandwidth percent) is only
allowed at the leaf node of a hierarchy. In other words, bandwidth (bandwidth
rate , or bandwidth percent) class cannot be attached with a child policy-map
containing queuing features. This is a restriction in software and may be
lifted in the future.
deployments where a Classic IOS QoS policy-map is being moved to a IOS XE
platform, the best option is to convert the intermediate node bandwidth
commands to bandwidth remaining commands. bandwidth remaining percent or
bandwidth remaining ratio commands could be used to achieve very similar