if master switch in stack reboots, will cause other member switches re

[Herman2018]

Hi, can someone pls advise whether if master switch in c3850 stack reboots (auto-reboot due to power failure, will cause other member switches reboot? 

Thanks in advance!

[balaji.bandi]

If the master switch reboot (only 1 ) rest of them have Power, next hot standby becomes master.

When the master switch reboot and come back, it will be part of the stack (it can not be master again)

Operationally there is no effect in the network (since the rest of the members work as expected) - that is the advantage of stacking.

if you like to fix this you need to reboot the whole stack

[Joseph W. Doherty]

It should not.

However, losing the master switch might not be completely hitless to traffic using the other stack's switches.

Unsure whether same applies to 3850s, but on the prior 3750 series, losing the master would cause a L3 hit (if switch running L3) if NSF not correctly configured.  Further, losing the master could cause the stack's MAC address to change, also if switch stack not configured to preclude.

In cases where the two prior conditions were not properly configured to preclude (the default), traffic using the remaining stack members could have traffic interrupted until stack elected a new master and stack "reset" itself with its L2 and/or L3 neighbors (usually this takes some number of seconds).

[Herman2018]

Thanks both of you! the strange thing is our master switch rebooted, then other members also auto-rebooted. 

[johnd2310]

Hi,

Run the "show version" command and have a look at the "Last reload reason" This might give a clue on what caused the reload.

Thanks

John

[Leo Laohoo]

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@johnd2310 wrote:
Run the "show version" command and have a look at the "Last reload reason"

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For classic IOS, yes.  For IOS-XE, not a recommended method:  CSCux58649, CSCuz05771, etc.

[balaji.bandi]

yes that is the case others mentioned, if the power Loss (and you have only power input source - not dual different feeds or UPS feeds, if the master switch suppose to provide stack power then all will be lost and shutdown)

you need to provide more information,  how are they connected and what source power each device has.

what I have provided thinking other members have power source and master switch shutdown case.

[Leo Laohoo]

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@Herman2018 wrote:
if master switch in c3850 stack reboots (auto-reboot due to power failure

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Yes, if the stack is running a buggy firmware. 

"reboot due to power failure"?  If the stack is running on redundant power, nothing should have failed/rebooted.

[Herman2018]

Thanks all for your kind replies. 

yes, the reboot cause is "reboot due to power failure". there is no redundant power for every switch. but logically the member switches should not auto-reboot.

[Leo Laohoo]

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@Herman2018 wrote:
but logically the member switches should not auto-reboot.

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If this is IOS-XE, then this is dependent on the firmware of the stack because there are some firmware which, when the stack master crashes, the standby will also crash.  When this happens, "sh version" will say the reboot of the stack master/standby were either caused by a "power on" or "unknown".

[Herman2018]

@Leo Laohoo ,Thanks a lot for your advice ! 

Is it possible to fix this issue by upgrading the IOS-XE ? currentl version is 3.6.6E. 

[Leo Laohoo · Accepted solution]

Upgrade to the latest 3.6.X but do not be tempted to upgrade to 16.X.X.

[Herman2018]

Thanks Leo !