methods of interconnecting switches

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Mar 27th, 2008
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I have 3 switch stacks of 3750G switches. Each stack has 3 switches for a total of 9 switches. The are connected using two fiber links from switch to switch. Config basically looks like a triangle with a stack at each point and the dual fiber links as the sides of the triangle.

If I would have configured this I would have bundled the two fibers of each leg using etherchannel teams. I would then rely on spanning tree turning off one the legs of the triangle to prevent loops.

However I did not config this, I inherited it. Instead of using etherchannel the architect of the setup configured the uplink ports with the command "spanning-tree link-type point-to-point".

How does this differ from etherchannel? it looks like I am not getting the benefit of the doubling of the throughput between switches.

Also, when I do a "show spanning-tree" I was surprised to find only one port of one of the legs in blocking mode. Should both ports be in block mode?

Comments? Suggestions?



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i-kendall Thu, 03/27/2008 - 15:28
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I think you are correct, and your "architect" did not do the best job for you. I would re-configure it using etherchannel to maximise bandwidth between switch stacks. STP will sort out the links, but check using the show command to confirm all is ok. I think the link type point-to-point command just makes stp forward traffic quicker when something changes, but for most installations you don't need this it works ok without.

Hope it is ok for you.




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