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Fiber connection question to Cisco 3560 switch

Posted on 2011-02-14
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Last Modified: 2012-05-11
Hello, we are connecting a Cisco 3750 switch to a Cisco 3560 with Fiber. We have two SFP connectors in each switch. On the Cisco 3750, both connections are green. On the 3560, one is amber and one is green. We are able to send traffic from one switch to another but we aren't sure why one is amber. We want to combine the connectors so that we can send 2GB over the link. When we unplug either fiber connection on the Cisco 3560, the other connection turns green. My first question is why is one connection amber and secondly how do we combine the connections so that we can utilize 2GB. Thank you.
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Question by:jledbetter
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Ken Boone earned 1600 total points
ID: 34888714
So you have 2 fibers between switches which effectively creates a loop.  So spanning-tree would then just one of the ports down to break the loop.

What you want to do is setup an etherchannel connection between the switches using both of those ports on each switch.  This creates a virtual interface called a port-channel that looks like one connection from spanning-tree's viewpoint.  Then it will send traffic down both links

Here is a link that shows how to do this:
http://www.cisco.com/en/US/tech/tk389/tk213/technologies_configuration_example09186a0080094647.shtml
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Expert Comment

by:Ernie Beek
ID: 34888728
Check your fiber on the amber connection, it might be faulty/damaged/dirty. If possible try to replace the cable.

With Cisco you can create an etherchannel to combine the two connections: http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml
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by:foochar
foochar earned 400 total points
ID: 34888747
My recollection is that on the 3560 switches if a port is a spanning tree redundant port that the status light will turn amber.  The 3750 switch is probably the root switch for your spanning tree domain so all the ports will be green on it.  If you want to create an aggregated 2 Gbps link between these two switches you want to investigate configuring Gigabit Etherchannel on these switches which will bundle the two ports on each end into a single virtual port.
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Expert Comment

by:lrmoore
ID: 34889544
foochar is correct. The reason one is amber is because Spanning Tree has one link in block mode to prevent loop.
Suggestion: put both links into a channel group and both will come up green and both can be used at the same time.
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Author Closing Comment

by:jledbetter
ID: 34892164
Thank you for your help. I setup an etherchannel which gave me exactly what I needed.
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