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Two Cisco 3750 Stack Masters

We have seven 3750 TS48 Ethernet switches and two 3750 TS16 Ethernet uplinks in a stack configuration:

3750 TS16 Ethernet Uplink #1 (priority 15)

3750 TS48 Ethernet Switch #1 (priority 1)

3750 TS48 Ethernet Switch #2 (priority 1)

3750 TS48 Ethernet Switch #3 (priority 1)

3750 TS48 Ethernet Switch #4 (priority 1)

3750 TS48 Ethernet Switch #5 (priority 1)

3750 TS48 Ethernet Switch #6 (priority 1)

3750 TS48 Ethernet Switch #7 (priority 1)

3750 TS16 Ethernet Uplink #2 (priority 9)

This stack configuration works fine; however, if all switches & uplinks in the stack are powered off and then powered on together, we have seen the two 3750 TS16 Ethernet Uplinks on the ends become stack masters at the same time. We thought the top 3750 TS16 Ethernet Uplink should be the stack master because it has this highest stack priority (15).

Any idea why we are sometimes getting two stack masters during a POR?

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Re: Two Cisco 3750 Stack Masters

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.

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

5. The switch with the longest system up-time.

6. The switch with the lowest MAC address.

A stack master retains its role unless one of these events occurs:

?The switch stack is reset.*

?The stack master is removed from the switch stack.

?The stack master is reset or powered off.

?The stack master has failed.

Re: Two Cisco 3750 Stack Masters

Your problem is with the statement "if all switches & uplinks in the stack are powered off and then powered on together".

Always power the unit you want to be master up first, let it completely initialize, then power the rest up. One thing that is odd is that one TS16 should reboot after seeing another master in the stack unless there is a cable problem with your stack cable. I have seen our 3750's fail to recognize their stack ports (and become masters) until we fiddle with the cables a bit, and then they will reboot and come up as member switches.

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