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3750 stack master

If you need to force a particular unit in a 3750 stack to be master, is there a specific command to do that (without reloading)? We have a 3-unit stack where the master has the enhanced IOS image and the others do not. If the master loses power, OSPF is lost.


Re: 3750 stack master

*Mixing IP base (SMI) and IP services (EMI) in the same stack

This is not recommended

If you are going to do this?please at least buy 2 EMI, so if the master fails, the backup can still route traffic.

The stack master is elected or re-elected based on one of these factors and in the order listed:

1. The switch that is currently the stack master.

2. The switch with the highest stack member priority value.

Note: We (Cisco) recommend assigning the highest priority value to the switch that you prefer to be the stack master. This ensures that the switch is re-elected as stack master if a re-election occurs.

3. The switch that is not using the default interface-level configuration.

4. The switch with the higher priority switch software version. These switch software versions are listed from highest to lowest priority:

-Cryptographic IP services image software

-Noncryptographic IP services image software

-Cryptographic IP base image software

-Noncryptographic IP base image software

With the above explanation, and your current stack status, if all else is left at default, it would make sense that the current stack master is what it is since it got elected due to criteria number 4. It has EMI (or IP Services Feature set) if this master is to ever go away you will be left with 2 EMI in which the one with a lower mac address will become. Master election only happens when the master goes away, so to answer your question, the entire stack does not need to be reset but the current master must be reset in order for the new master (preferred either by priority or criteria described above) to retain master status.

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Community Member

Re: 3750 stack master

Can you handle reloading the other two switches? If so you could issue the 'archive copy-sw' command to copy the EMI IOS from the master to their flash partition, followed by 'reload slot 1', 'reload slot 2' (1 & 2 being the switch numbers that require the upgrade). Make sure that you dont reload the master. You can deterine the switch's number by the LED's or by 'sh switch detail'.

This way you dont have to reload the entire stack and you'll have the same version of IOS.

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