How do I determine what mode of STP is running

Answered Question
Feb 13th, 2009

Most of my switches are running 12.2.25 or later. That version is capable of running Rapid Spanning Tree (802.1w). The show run says "spanning-tree mode pvst", and the show spanning-tree vlan 1 says "Spanning tree enabled protocol ieee". I have never changed the STP defaults. Am I running 802.1d or 802.1w? thanks. jc

I have this problem too.
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Correct Answer by Giuseppe Larosa about 7 years 9 months ago

Hello Jimmy,

>> If I attempt to move to RSTP on all my switches capable of running RSTP, what is the worst that can happen?

that the move will be not effective if most of the switches are still running PVST and so there is no real faster convergence.

So you have to evaluate how much is important for your network to improve STP convergence time.

If supporting VoIP the ability to have sub-second convergence can help.

Hope to help

Giuseppe

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jimmyc_2 Fri, 02/13/2009 - 12:44

Hi Giuseppe,

I have mostly 4500s and 2960s, and they do seem to allow me to run the command "Spanning-tree mode rapid-pvst". Can I simply run the command on all the switches without any concerns? The cisco documentation is painfully unhelpful.

jimmyc

Giuseppe Larosa Fri, 02/13/2009 - 13:04

Hello Jimmy,

the devices that don't support the command are not able to support rapid per vlan STP.

for example C4500 in release 12.2(25)SG has only support for normal PVST

while in 12.2(37)SG it is supported

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/37sg/configuration/guides/spantree.html#wp1064592')">http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/37sg/configuration/guides/spantree.html#wp1064592

So I'm afraid that you should before upgrade the devices that can be upgraded in order to get the highest benefits.

even if the table 15-2 declares backward compatibility between Rapid PVST and PVST+.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst2960/software/release/12.2_46_se/configuration/guide/swstp.html#wp1166519')">http://www.cisco.com/en/US/docs/switches/lan/catalyst2960/software/release/12.2_46_se/configuration/guide/swstp.html#wp1166519

So there are IOS images that support 802.1W or also 802.1s (IEEE MST)

Be aware that there is also a pre-standard MSTP Cisco version out there.

Check your devices and plan IOS upgrades on them.

Hope to help

Giuseppe

jimmyc_2 Fri, 02/13/2009 - 13:25

I looked at both links you provided, and they do nothing to clear things up. Cisco goes out of their way to make things complicated.

Regarding your advice to load the latest images before move to RSTP, I would rather not, since the downtime would far outweigh the gain.

If I attempt to move to RSTP on all my switches capable of running RSTP, what is the worst that can happen? thanks. jimmyc

Correct Answer
Giuseppe Larosa Fri, 02/13/2009 - 13:31

Hello Jimmy,

>> If I attempt to move to RSTP on all my switches capable of running RSTP, what is the worst that can happen?

that the move will be not effective if most of the switches are still running PVST and so there is no real faster convergence.

So you have to evaluate how much is important for your network to improve STP convergence time.

If supporting VoIP the ability to have sub-second convergence can help.

Hope to help

Giuseppe

jimmyc_2 Mon, 02/16/2009 - 11:41

Hi Guiseppe,

Many of former work-mates worked for Telespazio, as they were initial partners on Iridium. One of my friends still on the program is from Milan. Go Team Jueventus.

Jimmyc

Giuseppe Larosa Mon, 02/16/2009 - 13:38

Hello Jimmy,

the world is small. :)

Juventus team is in a transition phase to a new major release just to use a Cisco language.

Best Regards

Giuseppe

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