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?


Thanks,

Diego


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i-kendall Thu, 03/27/2008 - 15:28
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Diego,


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.


Regards,


Iain

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