STP Message Age

The Message Age is a value contained within BPDUs which are used by the Spanning Tree Protocol (STP). The full contents of a BPDU can be found here: STP contents of a BPDU.

The Message Age is a value found within BPDUs that starts off at 0 when it is sent from the root bridge, and is incremented by one every time it passes through a non-root bridge. Once the Message Age reaches the Max Age value, the BPDU is discarded. It works kind of like a TTL found in IP packets, to prevent BPDUs from being relayed forever in a topology.

Links:

https://forum.networklessons.com/t/introduction-to-spanning-tree/853/211?u=lagapidis

https://forum.networklessons.com/t/rapid-spanning-tree-configuration/1139/21?u=lagapides

https://community.cisco.com/t5/switching/msg-age-and-max-age-in-rstp/td-p/2251614