STP Topology Advice

Unanswered Question
Feb 18th, 2010

Hello, I'm going to be adding a couple of 3560 switches to my production network. I want to implement STP and was wondering if someone could look at the attached drawing I created and tell me if it's feasible.

Trying to gain a better understanding of STP through actual implementation.

Suggestions welcome.


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Edison Ortiz Thu, 02/18/2010 - 13:53

Which is the current topology? The top or bottom one?

The Top topology is what I would suggest for a fully redundant design.

nelson.garcia Thu, 02/18/2010 - 13:56

Edison, the top one is what the topology will look like before STP converges and puts all the redundant links in a blocked or designated roles. The bottom picture shows what forwarding paths I would have preselected for STP to use. I'm just wondering if the bottom half looks ideal for a good STP implementation based on the top picture's redundant links. I hope this makes sense. That's why I have the word "Becomes" in the middle. Top becomes Bottom.

Jon Marshall Thu, 02/18/2010 - 14:05

What you have is perfectly feasible from an STP point of view.

The bottom diagram is for the active links only ie. the ones forwarding although  bear in mind STP does not block both ends of the redundant link ie. it actually only needs to block one of the ports.

Also it is worth mentioning that the bottom can be per vlan rather than for all vlans ie. you could make switch A root for all the odd vlans and switch B root for all the even vlans. That way you would actually use all uplinks and load-balance your vlan traffic at L2 across all links.


Edison Ortiz Thu, 02/18/2010 - 14:12

Yes, it looks fine but as Jon said - if you have a lot of Vlans, you may want to have Switch B be the STP Root for Odd Vlans and Switch A be the STP Root for Even Vlans

You can change the load balance via other methods as well, like the first 10 Vlans use Switch A as STP Root and the following 10 Vlans use Switch B as STP Root.

Create some load balance between links, that's the key point here.


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