What is the default maximum age timer for STP?

The default maximum age timer for Spanning Tree Protocol (STP) is 20 seconds. This timer is crucial in STP as it determines how long the information about a bridge's forwarding database is retained before being discarded if no further updates are received.

When a switch starts up, it generates a Bridge Protocol Data Unit (BPDU) that contains information about itself and its topology. The maximum age timer plays a critical role in ensuring that the network converges correctly and efficiently. If there are no BPDU updates for 20 seconds, the switch will assume that the previous information is outdated and will proceed with a new topology computation, which helps maintain a loop-free environment in the network.

This timer setting is important for network stability and ensures that changes across the network are updated within a reasonable period. The use of a 20-second default value helps achieve a balanced approach between network responsiveness and stability, allowing networks to adapt to changes without frequent disruptions.