Simple 3750 Switch Stack Question

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Oct 21st, 2009
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I have (4) separate 3750 switches, (3) are 24 port and a single 48 port. I was thinking of consolidating them into a single stack. I have read some of the white papers so I understand the process, but other than getting the IOS on the same version, is there any special considerations I need to make? Is there a problem with having one with 48 ports and the rest 24? Any reason I wouldn't want to stack them?

Will rate posts.

Thanks.

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jbrenesj Wed, 10/21/2009 - 11:08
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Cat3750s no matter their port density are meant to be stacked. You are right as the most common problems come from IOS or feature set mismatches but as long as having a single management unit with no severe performance issues, having a stack is a real relief when configuring.


I am sure you read this doc but it basically tells all you need to know about stacking 3750s


Managing Switch Stacks

https://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_40_se/configuration/guide/swstack.html

mparella Wed, 10/21/2009 - 11:12
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Great, thanks for your input! So just to be clear there shouldn't be a issue that one of the switches is a 24 port and the others are 48 correct?

And lastly, when I create the stack, will the orginal configuration on teh ports remain intact? For example my vlan configuration and port setting?

thotsaphon Wed, 10/21/2009 - 11:12
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Michael,

- Properly be the same IOS on all switches

- No problem to mix 48-port and 24-port

- 32 Gbps for backplance when using stack cables. This is a reason why we like using uplink ports to connect them together. (J/K)



HTH,

Toshi

jbrenesj Wed, 10/21/2009 - 11:14
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A few things I can recall:


- If you stack a Catalyst 3750-12S with other 24 or 48 port switches there's a difference in the SDM template as the 3750-12S has an "aggregator" type of template that the other models don't have.


Configuring SDM Templates

https://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_40_se/configuration/guide/swsdm.html#wpxref79309


- cross-stack EtherChannel (meaning a channel using gi1/0/1 and gi2/0/1 for instance) can't be used with dynamic modes (PAgP or LACP) on older IOS versions. Use channel-group mode on

thotsaphon Wed, 10/21/2009 - 11:26
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Michael,


Lastly, when I create the stack, will the orginal configuration on teh ports remain intact? For example my vlan configuration and port setting?


- Trying to build a stack. It will assign a swicth number for each switch. The number will then use to reference the new port number. You have to re-configure things for sure. (grin)


HTH,

Toshi

Joseph W. Doherty Wed, 10/21/2009 - 11:33
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"Is there a problem with having one with 48 ports and the rest 24?"


Any 3750 series can be stacked together (you can also mix 3750 series with 3750-E series in same stack).


There are SDM templates (additions) that are unique to just one model, the 12 port SFP 3750 (as also noted by another poster).


"Any reason I wouldn't want to stack them?"


Biggest issue with stack, when you want to upgrade you need to bounce the stack. If you have separate units, with redundant paths, you might cause less network interruption. This isn't usually an issue if you can schedule network maintenance down time.


Another issue, stack ring can be a bottleneck. More of an issue with 3750 stackwise (vs. 3750-E stackwise+) and as stack size increases (max 9 units). If this is a concern, you're probably need to consider the 3750-E series and/or a chassis that provides a true fabric between blades (e.g. 4500, 6500).


You do want to use the same IOS version on all stack members (as noted in another post), however they will work with different feature sets.


"And lastly, when I create the stack, will the orginal configuration on teh ports remain intact? For example my vlan configuration and port setting?"


There are special considerations merging existing configured 3750s since the stack becomes one virtual switch (runs one config). I.e., believe some member switch configuration information could be lost, and pre-existing configurations might impede stack merge (as also noted by another poster).

thotsaphon Wed, 10/21/2009 - 11:38
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Joseph,

That's such a good explaination.


Rated it as usual. (grin)

Toshi

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