Logical Systems and Bandwidth Oversubscription
You can manage bandwidth at both the physical and logical interface level. However, if more than one logical system shares the same physical interface, the interface might become oversubscribed. Oversubscription occurs if the total bandwidth of all separately configured maximum bandwidth values for the interfaces on each logical system exceeds the bandwidth of the physical interface.
When displaying interface bandwidth information, a negative available bandwidth value indicates oversubscription on the interface.
Interface bandwidth can become oversubscribed when the configured maximum bandwidth decreases or when some flow bandwidths increase because of a configuration change or an actual increase in the traffic rate.
Interface bandwidth can become available again if one of the following occurs:
- The configured maximum bandwidth increases.
- Some flows are no longer transmitted from interfaces, and bandwidth reserves for them are now available to other flows.
- Some flow bandwidths decrease because of a configuration change or an actual decrease in the traffic rate.
Interfaces that are rejected for a flow because of insufficient bandwidth are not automatically readmitted, even when bandwidth becomes available again. Rejected interfaces have an opportunity to be readmitted when one of the following occurs:
- The multicast routing protocol updates the forwarding entry for the flow after receiving a join, leave, or prune message or after a topology change occurs.
- The multicast routing protocol updates the forwarding entry for the flow due to configuration changes.
- You manually reapply bandwidth management to a specific flow or to all flows using the clear multicast bandwidth-admission operational command.
In addition, even if previously available bandwidth is no longer available, already admitted interfaces are not removed until one of the following occurs:
- The multicast routing protocol explicitly removes the interfaces after receiving a leave or prune message or after a topology change occurs.
- You manually reapply bandwidth management to a specific flow or to all flows using the clear multicast bandwidth-admission operational command.
