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cross connecting 3750 stacks

I'm new to Cisco switches.

I need to connect two 3750G stacks. One stack consists of 3 x 3750G-48PS and 2nd stack is 3 x 3750G-24TS. Since all switches have 4 SFP ports I would like to use them to create 3 3Gb etherchannels in a full mesh and redundancy.

stack1 Gi1/0/49 - stack2 Gi1/0/25

stack1 Gi1/0/50 - stack2 Gi2/0/25

stack1 Gi1/0/51 - stack2 Gi3/0/25

stack1 Gi2/0/49 - stack2 Gi1/0/26

stack1 Gi2/0/50 - stack2 Gi2/0/26

stack1 Gi2/0/51 - stack2 Gi3/0/26

stack1 Gi3/0/49 - stack2 Gi1/0/27

stack1 Gi3/0/50 - stack2 Gi2/0/27

stack1 Gi3/0/51 - stack2 Gi3/0/27

Is this overkill or am I headed in a right direction? I have only the default VLAN so I understand that only one etherchannel is used for cross stack connection. Will this achieve auto failover?

Fred

8 REPLIES
Hall of Fame Super Bronze

Re: cross connecting 3750 stacks

Fred,

You are heading in a right direction and your configuration will achieve auto failover.

I don't think redundancy can ever be an overkill :)

Silver

Re: cross connecting 3750 stacks

Are these switch stacks physically close enough to connect with a stack cable?

New Member

Re: cross connecting 3750 stacks

they are about 100ft away and can't be stacked all together.

Purple

Re: cross connecting 3750 stacks

If you are using the stacking cables in the back of each of these stacks then it seems like major overkill on the connections between the boxes , hard to believe you would need that kind of bandwidth between the boxes but I don't know your traffic patterns . I would think 1 crosstack etherchannel ( 1 connection between each switch in the stack ) between the boxes would be enough .

New Member

Re: cross connecting 3750 stacks

Thanks for replying.

At first I was think to just create one etherchannel between the stacks but then I thought if we brought down the switch hosting it for any reason then there goes the connection. So I thought I should have 2 etherchannels but then I am thinking if I have 2 I might as well have 3 and fully mesh these stacks. Is this still overkill? Either way the bandwidth between the stacks will be capped at 3Gb. Is that such a huge bandwidth typically?

Purple

Re: cross connecting 3750 stacks

Not sure what you mean by "if we brought down the switch hosting it" , if you mean one switch in the stack then you would not lose your connection . The etherchannel would consist of one connection out of each switch in the stack on one etherchannel , the data would continue to flow over the other 2 links in the etherchannel. If you have one etherchannel consisting of one connection out out of each switch in the stack then you have 3 redundant gigbit connections , highly unlikely you would lose all 3 and this simplifies the config by only having one ehterchannel and saves money by not having to buy so many sfp gbics.

New Member

Re: cross connecting 3750 stacks

I thought I read that if I had two stacks A and B, I can only create a channel from one switch on stack A to 3 switches on B; and if I did a one-one connection it can't be combined into one channel. I would like make the interstack pipe larger than 1Gb.

Appreciate all your help.

Purple

Re: cross connecting 3750 stacks

We recently did it across a 2 switch stack to 2 other 3750's without a problem so I have no reason to believe a 3 switch stack wouldn't work , i am assuming though you are using the stacking cables in the back though . If you do this though you can not let the etherchannel dynamically create itself in crossstack etherchannel you have to force the channel on instead.

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