[ednog] Anyone deploying MSTP and/or RSTP as alternatives to spanning tree?

Laura Grill-Kristoff laura at rocky.ittns.northwestern.edu
Thu Apr 28 10:47:48 EDT 2005

On Tue, Apr 26, 2005 at 06:19:37PM -0500, David Farmer wrote:
> The following is the design Guide we used to help implement.
> http://www.cisco.com/application/pdf/en/us/guest/tech/tk621/c1501/ccmigration_09186a0080174993.pdf

thanks I'll take a look.

> We had one small problem.  We configure new switchs via a script, the 
> old script turned on VTP before MST.  This wasn't a problem until we 
> got to our largest Core Node that has 178 VLANs.  So, 3750s support 
> 128 spanning tree instances and default to PVST (Per VLAN Spanning 
> Tree) as do most Cisco Switches.  So when VTP was enabled it tried 
> to create 178 spanning trees, it could so it disable Spanning Tree for 
> about 50 VLANs, and they remain disable after MST was configured. 

We ran into the very same problem with VTP on one of our large cores. We
ended up transitioning away from VTP and putting all our access switches in
transparent mode.   I guess MST is another way to handle that problem.

> And then an accidental loop got created during an install, and BAM!!!  
> Actually, this happened many time before during install, crossed fibers, 
> etc...  But this time we didn't have spanning tree on a bunch of VLANs.  

yeah, we got hurt by that a couple of times as well... hence the move to
transparent mode.

Thanks a lot for all the info.


Laura Kristoff
IT Telecommunications and Network Services
847-491-4094   l-grill at northwestern.edu

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