The following types of interfaces support global UCMP:
Ethernet interfaces
GE interfaces
Eth-Trunk interfaces
Global UCMP requires that multiple outbound interfaces that support global UCMP exist. If one of these interfaces does not support UCMP, traffic is evenly distributed on other interfaces, regardless of the bandwidths of these interfaces after global UCMP is enabled.
After global UCMP is enabled on all interfaces that support UCMP, all routes are delivered to the interface board and bandwidth information about load balancing on each outbound interface is delivered in the same way as interface-based UCMP. Then, the interface board calculates the distribution ratio according to the bandwidth of each outbound interface.
When a large number of routes exist, a global command is set to avoid the pressure from delivering all routes to the system. The interval between enabling and disabling global UCMP is 5 minutes.
When the interface bandwidth changes because a member interface is added to or removed from a logical interface or a member interface goes Up or Down, the modules related to logical interfaces, such as the trunk, inform the interface management module of the new bandwidth of each interface. Then, the interface management module sends an event message informing the FIB module of bandwidth changes. After verification, the FIB module informs all interface boards of bandwidth changes on interfaces. Consequently, the interface boards calculate the traffic ratio. If routing calculations are caused by interface bandwidth changes, the FIB module resends FIB entries.
Processing interface bandwidth changes takes time so that the CPU may be busy processing frequent changes of interface bandwidths. To avoid this problem, you can set an interval for reporting changes of interface bandwidth to interface boards. If the interface bandwidth changes multiple times within the interval, the latest bandwidth is reported to interface boards.
If global UCMP is enabled, interface-based UCMP cannot be enabled. Similarly, if interface-based UCMP is enabled, global UCMP cannot be enabled.