Cutting the time a switch port will take to go in forwarding state

[samisalim]

For a lab enviroment, how to set the time a port will take to go from learning to forwarding stage, if LAN topology got changed. For instance to 10-seconds.

I have gone through many readings, I couldn't find clear cut answer, other than recommendations to enable spanning-tree porfast and spanning-tree bpdu port guard enable.

Appreciate your help.

[b-ulrich]

Hi, what exactly are you trying to accomplish? Enabling portfast is the only way I know to speed this process up. The timers within spanning-tree are there for a reason and the steps it goes through. Bpduguard protects against unwanted switches added to your network, basically. If it receives a bpdu, it puts the port in err-disable.

[samisalim]

Thanks for your input. I am about to cut the time spent for the ports statically assigned to a specific vlan, to go to forwarding stage in 10-sec. if lan topology has occured.

Thanks

[Georg Pauwen]

Hello,

you cannot set the timers per port, but you can set them per Vlan. The max-age timer (20 seconds by default) and the forward-delay timer (15 seconds x 2 by default) can be set to the minimum with the following command:

spanning-tree vlan x forward-time 4

spanning-tree vlan x max-age 6

These are the minimum-configurable values.

Spanning-tree portfast skips the listening and learning phase of STP and moves the port directly into the forwarding state. However, enabling this feature is only recommended for ports that connect to end devices, such as PCs or servers, because the port will not properly detect a spanning tree loop when this feature is enabled on a port. The bpduguard feature is usually used in combination with the portfast feature: if a BPDU is detected, which means that there is another STP-capable device connected to that port, the port is shut down...

Does that make sense ?

Regards,

GP

[samisalim]

How about "spanning-tree vlan x hello-time" does it have any role to play in this aspect ?.

Thank you

[williamwbishop]

Perhaps you explained it and I missed it, but are you trying to cut the time from switch to switch, or from switch to PC?

For pc ports, use portfast, with bpduguard

For switch to switch, use uplink fast.

It is best not to modify the timers individually, if you have to do it, use the scripts, which make the changes for you and maintain the proper balance.

I can't see many instances where the default does not work best, unless it is an incredibly small or and incredibly large network.