Uplinks between switch stacks

[serotonin888]

Hi

I have a stack of 2 x 3650 at the core and an access layer stack of 4 x 2960X.

I was planning on linking these with 4 x 1GB copper connections. Any thoughts on how this should be cabled?

I was thinking 1gb copper uplink from each of the 2960X stack members split across the stack of 2 x 3650?

The uplinks would be in an etherchannel.

Or are there other recommendations?

Thanks in advance.

[ghostinthenet · Accepted solution]

It sounds like you have a good approach, though I would consider doing two to the 2960X stack master and two to the backup in order to cut down on excessive cross-stack traffic. Also, make sure you're using LACP and not raw EtherChannel. Last I checked (it has been awhile) raw EtherChannel wasn't supported for cross-stack applications.

[serotonin888]

Thanks - Based on all the feedback I'll probably use 2 gig links from the master (one to each of the 3650's) and then 2 from another switch in the 2960X stack (one to each of the 3650's) . I'll configure etherchannel with LACP active. The 2960X is just an access layer switch for end users so I'm not expecting high volumes for traffic to the 3650 stack. But I'll monitor the traffic on the uplinks and can tweak the load balancing algorithm as required.

Thanks to everyone who responded.

[Joseph W. Doherty]

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Posting

I don't know if this applies to 2960X series, but with 3750X series, Cisco recommends to avoid placing uplinks on master switch.

Also, although placing pairs of uplinks on two 2960Xs will work fine, if one of those 2960Xs fail, you lose half you uplink bandwidth vs. only losing a quarter.

BTW, the two prior conflict, but often such is involved in network design.  ;)

[ghostinthenet]

The potential loss of half of the uplink is a more important consideration than inefficient use of the stack bandwidth. Rethinking things, Joseph's suggestion of splitting across four switches sound like the better plan.

[Nishan Thevathason]

Hi Jody,

Thank you, But I have raw EtherChannel configured in between both Core switches setting Channel Mode on. Should I change it with LACP, or it is fine. and my question is remaining same "Where Should be uplink place on the stacked switch from both Core switch"

[Joseph W. Doherty]

What exact model 3650s?

How did you "stack" the 3650s?

[ghostinthenet]

Good point. I just assumed he was using the standard StackWise-160 cables, but one person's "stack" may be another's Ethernet cross-connect. :)

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of   the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Jody, laugh - oops - actually I had 3560s in mind - which is why I was wondering about stacking, but you do raise a good point about whether stack cables were used.

For OP, yes you could have a gig link from each switch, two to each 3650.  However, that won't, I believe guarantee you any or much better performance as Etherchannel should distribute the load across the links regardless of physical switch destination.

You'll want to insure, though, you're using the best load balancing algorithm for each direction.

[ghostinthenet]

100% agreed on the load-balancing algorithm.

The recommendation of two to each of the master and backup was more to avoid duplicating traffic across the StackWise connections than anything else, but the bandwidth available should make that a minimal factor anyway.

[serotonin888]

Thanks Jody - We'll be using stack modules in the 3650 and 2960X's (true stacking).