Which typ of STP to use?

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Feb 4th, 2008
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If you've got a network consisting of all Cisco equipment and you've maybe only got a couple of VLANS should you run RSTP rather than the default PVST? And if you've got a lot of VLANS should you run MST? I've been doing quite a bit of reading in the last few weeks and it seems to me like the standard PVST should not be used unless you've got a mix of Cisco and other kit. After all RSTP is better and you don't have to bother with Uplinkfast or Backbonefast as they're built in. And if you're running a lot of VLANs then wouldn't MST be the logical choice as it can load balance and doesn't produce many BPDUs?

I've only seen ieee in use though for some reason. Are there many people using RSTP or MST?

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glen.grant Mon, 02/04/2008 - 04:38
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PVST+ will work fine in most instances . If faster convergence is of utmost importance to you then use RSTP .

Peter.D.Brown Mon, 02/04/2008 - 07:01
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Yes I think it is but it's backwards compatible. It is the default mode for all Cisco kit. When you issue the command 'show spanning-tree' it is listed as ieee. What I was wondering is why, if the layer 2 network is all Cisco rather than a mix of manufacturers, people tend to stick with the default of PVST+ when it is much slower to converge than RSTP (actually it is RPVST+ in Cisco). Also RPVST+ does not take any extra configuration (in fact it takes less, no Uplinkfast or Backbonefast to worry about). I know the default works ok but why would you use it in preference to RPVST+ if all the kit is Cisco? Im assuming that maybe that a lot of people that install network kit don't know a much about spanning tree other than the fact that the default works without any configuration so they don't bother to change it, even though the change would be just the one line: 'spanning-tree mode rapid-pvst', and the result would be much faster convergence. I was wondering too if there are any caveats with using RPVST+ that I don't know about, hence the original question. I can't see any reason to implement PVST+ in preference to RPVST+ (except with a mix of Cisco and non-Cisco kit).

glen.grant Mon, 02/04/2008 - 07:58
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I think in new installs rstp does get used . A lot people stay with pvst because that is what is in the rest of the currently installed network so it would take a whole project to go thru and change it out and frankly the way things have been downsized in most places there isn't enough time or people to do this . . In a new install there really is no reason not to use it.


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