Spanning Tree - Enabling STP on a 6500 L2 switch

[yperriman]

We have discovered we have two switches that do not have STP enabled on them. What will be the impact on the live working ports of enabling STP on the switch.

I have looked at the Cisco documentation about the various STP timers but i could not find anything that could clearly say how long the port will remain in a blocked state for before going to listening/learning and finally forwarding.

Anyone out there that can help?

[Amit Singh]

Hello,

When you enable the STP on the switch and you have uplinks connected to it, it will take around 50 seconds for the STP to stabalize. I will suggest you to introduce these switches after office hours in a live environment.

In blocking state, the switch port waits to receive a BPDU from the other end.When it receive a BPDU the port enters immediately into learning state.

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_guide_chapter09186a0080160a5b.html#wp1020487

HTH,

-amit singh

[yperriman]

Thanks for both the responses. THat is really helpful. I agree that the change should take place in our greenzone.

Once again thanks.

YP

[vijayasankar]

Hi,

Good that you have noticed that STP is disabled on these switches. Event If some one introduce a loop unintentially, it will create problems in the network.

What is STP protocol that you are already running in your network? 802.1d,802.1w,802.1s..?

Have a look at the following URL for understanding the various STP timers in general.

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094954.shtml

Configuration steps for enabling 802.1d and 802.1s on 6500 series

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_guide_chapter09186a008007e71a.html#wp1020442

To ensure that spanning tree doesn't block the edge ports while converging, you can use the feature called port fast.

There are other similar features available in STP, to fine tune the protocol based on your required.

Have a look at this URL for additional STP features like port fast, uplink fast, backbone fast which might be of interest.

http://www.cisco.com/en/US/products/hw/switches/ps663/products_configuration_guide_chapter09186a00800f0e23.html

Hope this helps.

-VJ