topology changes can trigger excessive packet flooding in your STP network.
With Rapid STP or Multiple STP (MST), a change of the port's state to
forwarding, as well as the role change from designated to root, can trigger a
topology change. Rapid STP immediately flushes the Layer 2 forwarding table.
802.1D shortens the aging time. The immediate flushing of the forwarding table
restores connectivity faster but causes more flooding.
In a stable
topology, a topology change should not trigger excessive flooding. Link flaps
can cause a topology change, so continuous link flaps can cause repetitive
topology changes and flooding. Flooding slows the network performance and can
cause packet drops on an interface.