After Partial Power Outage, Two Switches in Stack Reporting As Master

[FoxtrotRomeo]

We had a UPS failure last week in which a breaker on the UPS tripped throwing everything plugged into that PDU offline.  That included half the switch stack.  When power resumed, the network is operating normally but I noticed that now two of the five switches in the stack are reporting that they are the master. I assume that when the power went off, the Master went down and thus an election occured between the members that were still up. 

What do I need to do to fix this without screwing up the port configurations?  When I do a remote session to the switch and run show switch it shows the stack still intact.  Even the web console shows the stack still intact.  Can I simply just power cycle the switch that's saying it's a master and power it back on?

[Reza Sharifi]

Hi,

If the rest of the stack is working fine.  You can turn off the second master (the one that is not should to be) and than turn it back on.  When you are on the master command line, what is the output of sh switch det?

Also, if you don't have priority assigned to your switches (master being the highest) it may be a good idea to do so.  This way you always know which switch is the master.

Power cycling should be done during an outage window

HTH

[FoxtrotRomeo]

sh switch det

shows:

Layer-2-Switch#sh switch det

Switch/Stack Mac Address : 001e.1458.d500

                                           H/W   Current

Switch#  Role   Mac Address     Priority Version  State

----------------------------------------------------------

*1       Master 001e.1458.d500     1      0       Ready

2       Member 001e.14af.0080     1      0       Ready

3       Member 001e.14ae.e180     1      0       Ready

4       Member 0024.50db.d480     1      0       Ready

5       Member aca0.1614.8800     1      0       Ready

         Stack Port Status             Neighbors

Switch#  Port 1     Port 2           Port 1   Port 2

--------------------------------------------------------

  1        Ok         Ok                2        3

  2        Ok         Ok                5        1

  3        Ok         Ok                1        4

  4        Ok         Ok                3        5

  5        Ok         Ok                4        2

Layer-2-Switch#

[Shawn Thomas]

As mentioned:

You have to set the priority of the switches and that will determine which one is the Master switch.

If they are 3750s then 15 is highest priority; if 2960s set Master to priority 14.

If the priorities are the same then the switch with the lowest MAC address will become the master if you dont change the priority.

You can also reboot individual members in the stack by doing the below command:

From global config mode.

reload slot # (number of member in the stack)