Mixing EMI and SMI images in a 3750 stack

Answered Question
Jun 4th, 2009

I'm considering going to layer 3 to my IDF's. How would this work? If I buy 4 switches with the SMI image and 1 with the EMI do they sync IOS version to the EMI or will only 1 switch have the expanded IP capabilities?

I have this problem too.
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Correct Answer by Collin Clark about 7 years 6 months ago

The switch cluster has the capabilities of the master switch. Let's say the master switch has EMI and you configure it with some EMI features. It then fails and an SMI switch becomes master, all those features are not supported and removed. That will cause more trouble than what it's worth to buy the correct image for all the switches.

Hope that helps.

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Correct Answer
Collin Clark Thu, 06/04/2009 - 07:41

The switch cluster has the capabilities of the master switch. Let's say the master switch has EMI and you configure it with some EMI features. It then fails and an SMI switch becomes master, all those features are not supported and removed. That will cause more trouble than what it's worth to buy the correct image for all the switches.

Hope that helps.

iyde Thu, 06/04/2009 - 13:01

Actually, when Cat3750 switches are staked together, they will get the same image, which is the image of the master switch. This means that you'll have a legal issue as well if you pay for one EMI and three SMI and ends up with EMI on all switches because the master has EMI.

Remember, when stacking you makes (in your setup) 4 physical switches look and behave as 1 logical switch. This means that you'll have same image on all in order to have consistency, and one unified configuration.

HTH.

Joseph W. Doherty Thu, 06/04/2009 - 16:48

I recall I looked into this issue when the 3750 were released and it was legal to run a stack on one "EMI" image, although illegal to actually have such an image loaded on other stack members' flash.

As to Collin's point, also recall stack election takes into account feature set and "EMI" should win over "SMI". So, as long as two stack members have a legal copy of the "EMI", your stack can tolerate failure of the the running stack master.

Assuming I have all the prior correct, upgrading the stack IOS is a bit more difficult since normally I believe the upgrade updates all stack member flashes. However, I believe it's also possible to upgrade individual stack stack members w/o breaking the stack apart.

[edit]

So, for your example of 5 stack members, believe it's legal to have, for instance, two with "EMI" image on flash (licenced for such) and three with "SMI" image on flash. Stack should elect one of the "EMI" member switches and stack will run and support "EMI" feature set. If the stack master fails, other stack member with "EMI" should continue functioning. (If more than 2 stack members fail, stack fails.)

iyde Fri, 06/05/2009 - 07:40

I must admit that I'm not sure regarding the legal part; it's an assumption based on the legal ways Cisco normally do business.

Regarding having ipbase in some flash and ipservices in other (current names for SMI and EMI, respectively) I believe that it will give functionality issues if you try that, and you'll definitely have to manually put the images in each switch' flash, as the normal (and preferred) way of upgrading by using the 'archive download-sw' command will put same image in all flash.

HTH

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