Overview of MSTP BPDU throttling

When an STP enabled switch is hit by an MSTP BPDU storm, the CPU usage rises and the manageability of the switch goes down. In the following figure, the switch is connected to a HUB where there is a loop. The switch generates a single MSTP BPDU, which goes through the loop in the HUB and results in a BPDU storm eventually. Since all STP packets are taken to the CPU for processing, CPU usage goes high and the switch response slows down. The switch can become unmanageable as a result of this BPDU storm. BPDU throttling will take care of BPDU storms automatically through rate-limiting.

Figure 11: MSTP BPDU path

BPDU throttling is enabled when the spanning tree in MSTP mode is enabled. When spanning tree is enabled, all modules and members are assigned corresponding throttle values from the configuration. The default throttle value is 256.

An option is also provided to enabling/disabling BPDU throttling. This option is enabled by default if the switch does not support “V1 modules”. The spanning tree is enabled in MSTP mode by default.