If you get 2 new switches then you have stack them separately and not mix them with your existing once since the IOS images are different.. Talk to your sales rep on the licensing price. You may get a dipper discount since you are stacking them. I know with the 6500 dual sup the only charge you for one IOS since one is active and the other one is stand-by.
I think you can upgrade only two switches to EMI as per the attached document
Master Switch Election The stack behaves as a single switching unit that is managed by a master switch elected from one of the member switches. The master switch automatically creates and updates all the switching and optional routing tables. Any member of the stack can become the master switch. Upon installation, or reboot of the entire stack, an election process occurs among the switches in the stack. There is a hierarchy of selection criteria for the election. 1. User priority—The network manager can select a switch to be master. 2. Hardware and software priority—This will default to the unit with the most extensive feature set. Catalyst 3750 switches with Enhanced Multilayer Software Image (EMI) versions take precedence over Standard Multilayer Software Image (SMI) versions. 3. Default conﬁguration—If a switch has pre-existing conﬁguration information, it will take precedence over switches that have not been conﬁgured. 4. Uptime—The switch that has been running the longest is selected. 5. MAC address—Each switch reports its MAC address to all its neighbors for comparison. The switch with the lowest MAC address is selected.
Cisco IOS Images Must Be Identical The Cisco StackWise technology requires that all units in the stack run the same release of Cisco IOS Software. When the stack is ﬁrst built, though, the units can have SMI and EMI version differences. This will automatically cause the EMI versions to become the master switches so the stack can use routing functions. However, the ﬁrst time you upgrade the Cisco IOS Software release, all units will be required to run the same SMI or EMI version as the master.
note in the above document it stated on the same release even if they SMI and EMI
Can I upgrade only two switches to EMI IOS and leave another two switches to SMI IOS?
No you can't. Here's the reason:
1. Firstly, the entire stack has to be using the SAME FEATURE SET because you can't program, for example, BGP routing on an IP Base switch. Remember that your ENTIRE STACK operates as one.
2. Secondly, presume that you did manage to get this running and you need TAC's help. They'll see what you've done and, most likely, raise their hands up in the air and tell you that they won't support a setup like that.
3. Lastly, it won't work because the stack will see that the new members are operating in a higher feature set and during a crash, will cause the entire stack to operate in "limbo" and totally un-responsive.
It is better to upgrade your stack to IP Services or DO NOT USE the IP Base software.
first I'd like to thank you for your reply but as you read in the above post ,theoretically you can mix the stack between SMI and EMI
note in the master switch election
2. Hardware and software priority—This will default to the unit with the most extensive feature set. Catalyst 3750 switches with Enhanced Multilayer Software Image (EMI) versions take precedence over Standard Multilayer Software Image (SMI) versions.
also note that:
When the stack is ﬁrst built, though, the units can have SMI and EMI version differences.
so if I have new solution not upgrade I think I can mix the stack between SMI & EMI
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