3750 Stack

Unanswered Question
Mar 14th, 2008

When stacking 3750s do the all have to be the same version (standard or enhanced) image in order to have redundancy as in if the master switch (which is an enhanced image) fails then the next in line switch (standard image)can take over the master role and perform the dynamic routing? I have heard a number of different opinions on this subject.


I have this problem too.
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adavenport Fri, 03/14/2008 - 10:41

Switches _must_ be running the same feature set

for them even to co-exist in a stack.

SW version must be close. Some minor revs can

stack together, but if the stack-ring protocol

has changed between versions, that won't work


Always best to match them before stacking.

Under some circumstances, the switches may

up/down grade themselves automagically, but

I've not had consistent results.

Hope this helps.


Roman Rodichev Wed, 06/18/2008 - 08:31

switches _don't have to_ be running the same feature set to co-exist in a stack.

Joseph W. Doherty Fri, 03/14/2008 - 16:33

My understanding for 3750s (not 3750-E), different feature sets are supported within a stack. Stack election chooses the "best" which becomes the running image. If only one member has "best", and that member fails, next "best" elected, which could lack features of the prior version (e.g. loss of routing capability).

mbroberson1 Sun, 03/16/2008 - 17:09

I had a TAC base about this recently and Cisco says best practice to have the same version on all switches.

chris.howard Mon, 03/17/2008 - 05:47

Thanks for all your responses. It sounds like best practice is to have the 3750 all the same image but you can mix images but you lose some of the inherent capabilities of the 3750 stack.

Roman Rodichev Wed, 06/18/2008 - 08:29

You only need your stack master to run IP Services, and all other switches can be purchased with IP Base feature set. Rule states that the switch with higher feature set (IP Services) will become the master.

There's a caveat though.

The switches that boot up faster will participate in the election process, so if you boot switches at the same time (quite normal event) the IP Base will become master, because IP Services switches takes slightly more time to boot. So to prevent this from happening, you should configure higher priority on the switch with IP Services feature set.

Also a good idea to have a second switch IP Services image which will act as a backup master (set a priority for it between 1 and the master priority).

So to answer your question, NO, you don't have to buy IP Services image for all switches in the stack.


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