Connecting 2 Clusters of 3750's via Fiber

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Dec 7th, 2009
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I am installing a new network at a location.  The core of the network will be 2 clusters of 3750's.  Each cluster is 2 switches.  I am using the Cisco StackWise cable to connect the 2 - 3750's in the stack.  I am looking to connect the 2 cores of the network via fiber optic cable.  I am looking to use 2 cables for redundancy and increased bandwidth.


My question is this.  Can someone share with me their experience with this?  I am thinking what I need to do is use a Bridge Group for the 2 fiber ports but am not positive.  My other question is when using 2 fiber ports should I use one on each switch?  I would assume for redundancy this would be best practice but am looking for some advice.


Thanks in advance!!

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GRANT GATHAGAN Mon, 12/07/2009 - 13:29
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Why not simply etherchannel two ports from each cluster as dot1q trunks?
If you see enough traffic to warrant it, you could etherchannel additional ports on each cluster together, with a maximum of 8 ports per etherchannel group.


You *could* create etherchannel groups on each cluster with a port from each switch, but that would only be of use if you were worried about a physical failure.

vvasisth Tue, 12/08/2009 - 04:12
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I believe Etherchannel would be a good optyion for you as it will provide redundance as well as increased bandwidth..

However , if you want both links to be on 2 different switches on a stack that means you are reffering to cross stack ether channel. PAgP is not supported in a cross stacked switches and recommendation is for mode on.



In any case you would need atleast 12.2(25)SEC or higher inorder to configure a cross-stack etherchannel. Here are the links for the same:

Release Notes:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/12225sec/ol7454.htm#wp731959

- PAgP does not support cross-stack EtherChannels.
- After grouping the links into an EtherChannel, LACP adds the group to the spanning tree as a single switch port. 
- You should use care when using the 'on' mode. This is a manual configuration, and ports on both ends of the EtherChannel must have the same configuration. If the group is
misconfigured, packet loss or spanning-tree loops can occur.
- If cross-stack EtherChannel is configured and the switch stack partitions, loops and forwarding misbehaviors can occur.

This little information is an excerpt from the link below where you can find all the information regarding configuring Etherchannels in your 3750:

Configuring EtherChannels and Link-State Tracking
http://cco-sj-2.cisco.com/univercd/cc/td/doc/product/lan/cat3750/12225see/scg/swethchl.htm
#p1275628

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