Rapid Spanning Tree question for the gurus

mikeybinec

See attached. Theory tells me that in regular Spanning tree that the hellos are sent out every two seconds and if after 10 hellos and no response you have the max age timeout. What I don't get right now is that I have my 2960s in RSPT mode. Theory tells me the max age should be 3 hellos but my sh sp command still shows the max age is still at 10 hellos before the max age kicks in even though it is in RSPT. Am I making sense? Thanks gurus

davenull

I remember reading something about MaxAge not even being needed in RSTP, and it's only there for compatibility with STP. On a side note, you need to know that in regular STP only the root bridge's timers are relevant, the local timers are only there if the root bridge goes offline. This is not the case in RSTP though.

This doesn't really answer your question, but maybe somebody else can chime in.

OfWolfAndMan

For RSTP, this information can be relevant in two cases:
1. Another switch is using the traditional 802.1d. In this case, legacy timers are used
2. A device on the end of the port (Lets say a computer) doesn't have portfast configured and will be subject to legacy spanning tree

People tell you to configure portfast for the reason of bypassing the forward delay of 30 seconds, but there's more than one reason. One for the reason stated above and the second reason being whenever a user disconnects their device from the port for some reason and portfast is not enabled, it relays a Topology Change Notification throughout the STP topology. This causes every switch in the topology to flush it's CAM table and ARP resolution must be redone. The point of the story is use portfast on your users' ports!