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Spanning Tree questions

Valued Contributor

Spanning Tree questions

Some questions concerning Spanning Tree that I have not be able to find the answers for. If anyone knows the solution for one or more of these questions I would be very grateful.

1. In your opinion, which Spanning Tree method is mostly used today? STP/RSTP/MSTP?

2. If the root switch fails, how fast will a new root be elected? Is the time different between STP/RSTP/MSTP?

3. The original STP use the timer 15 sec in listening and 15 sec in learning state for a port. In RSTP and MSTP, is this changed? I found some information saying the timers are the same, but the ports (both end-ports and inter-switch-links) seems to be very fast into forwarding mode.

4. If you mix STP and RSTP switches, do you have to change all path-costs on the RSTP switches to make it work?

5. Is it known why Procurve switches does not give trunked ports better cost values? I think Cisco does this at least. Procurve gives the trunk port a better port priority, but that will not "help" much.

M Macleod
Occasional Contributor

Re: Spanning Tree questions

1) - Its subjective, but I would say a combination of RSTP and MSTP
2)On our Network, it is sub-second, we run MSTP
4) Not that I am aware of, but someone better qualified than me would have to help you there
5) we have manually set the trunk priorities
Jarret Workman
Frequent Advisor

Re: Spanning Tree questions

Hi Ric,

To help answer a few more of these questions:

3) RSTP and MSTP put ports in a forwarding mode during the learn state of a spanning-tree topology change while original STP blocked all ports for about 30 seconds during the learn.

4) RSTP is backwards compatible with STP, so you should not have to change the path costs to make it work.

5) I'm not 100% clear on the question, but the default cost of a port is 8. When you enable spanning-tree, all trunk ports are automatically changed to a priority of 4, which should give them a higher priority than a non-trunked port.