Mixing STP versions?

[kghutton]

We are extending our LAN infrastructure across a SONET based link from our ISP. It is bridging 2 data centers, one we are currently in and one we are moving to. The link has 3550's at either end connected by single mode LX fiber. Each 3550 is then connected to Core swtches ( 2 6509's at each location) via 2x100Mb etherchannel. My question relates to having 2 very different versions of STP running at each location. Our current location has a root switch (6509) running Cat OS 5.5 We can not upgrade due to logistical problems. We want to run RPVST+ at our new location and only have PVST as the current spanning tree type (there are no options in the 5.5 version of Cat OS for stp). Since these 2 locations are connected via a layer 2 link, is this advisable? We want the current root switch to remain the root switch until we move all the equipment and shut down the layer 2 link. Will the 2 verssions talk "nicely"? Will one of the new switches running RPVST+ take over as root due to having a "better" version of STP. Is it possible to use PVST on the new switches and change that to RPVST+, once the move is done, without causing the network to transition all stp participating ports causing network outages?

Thanks for any input.

Kevin

[Georg Pauwen · Accepted solution]

Hello Kevin,

in a mixed environment, if one switch talks 802.1D and the other RSTP, the RSTP switch will simply revert to 802.1D (and obviously the benefit of faster convergence will be lost). See the link below for a detailed explanation.

The root bridge is not affected, the election keeps depending on cost and priority.

Not sure about the convergence when you upgrade, my guess is that there is a brief outage, I would execute the change after hours...

Understanding Rapid Spanning Tree Protocol (802.1w)

Convergence with 802.1d

http://www.cisco.com/en/US/partner/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml#converge

HTH,

GP

[kghutton]

That is what I thought but wanted a gut check.

[milan.kulik]

Hi,

here is another good document:

http://www.cisco.com/application/pdf/en/us/guest/tech/tk621/c1501/ccmigration_09186a0080174993.pdf

Regards,

Milan