2960 Stack Election

[Patrick McHenry]

At the moment Switch 2 is the Master. I've loaded a new image to flash1 and flash2. When I go to reload will Switch 1  become the Master because of it's lower MAC address?

Also, if Switch 1 takes over and becomes the Master will this affect anything?         

SWITCH-Stack#sh sw detail
Switch/Stack Mac Address : b414.8938.3c80
                                           H/W   Current
Switch#  Role   Mac Address     Priority Version  State
----------------------------------------------------------
1       Member b414.8938.2800     1      1       Ready
*2       Master b414.8938.3c80     1      1       Ready

         Stack Port Status             Neighbors
Switch#  Port 1     Port 2           Port 1   Port 2
--------------------------------------------------------
  1        Ok         Ok                2        2
  2        Ok         Ok                1        1

Thanks, Pat.

[Reza Sharifi]

Pat,

Here are the criteria for the master election:

Making a Specific Switch the Stack Master and Master Election Rules

Stack Election Rules

When  multiple physical members are present in the stack, one of the members  will be elected as the stack master. There can only be one master and up  to three backups 1:3.

The election rules used by FlexStack in choosing a master are applied in this order:

1. Switch that is the current master

2. Switch with higher priority

3. Switch that has configuration file

4. Switch with highest uptime

5. Switch with lowest MAC address block

I recommend giving higher priority to which ever switch you want to be the master.  This way you always know what switch is the master.

more info:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/white_paper_c11-578928.html

HTH

[Patrick McHenry]

So, it looks like when I reboot the current Master will become the Master after reboot as it is the Master before the reboot, correct?

If the Master changes to Switch 1 by chance, will this affect anything?

Thank you, Pat.

[Reza Sharifi]

Yes, switch 2 should be the master again.  Even if switch 1 is the master after the reboot, as long as you have the same exact IOS feature set and license, it should not effect anything. But again If you give switch 2 a higher priority than that switch will always be the master.

HTH

[Leo Laohoo]

So, it looks like when I reboot the current Master will become the Master after reboot as it is the Master before the reboot, correct?

If you reboot the Master (and ONLY the Master), the next Slave will become the Master.

If you boot both one-by-one, whoever boots first will be the Master.

If you boot both simultaneously, whoever has the lowest MAC address will be the Master.

[Patrick McHenry]

Leo,

So, you are saying that just because Switch 2 is the Master at the moment - it doesn't mean it will be the Master after reload. If I reload both at the same time the lower MAC will be the Master?

My real concern is not which switch will become the Master, I just want to know if it will really affect anything if Switch 1 becomes the Master after reload? What changes other than Switch 1 possibly becoming Master?

Thanks, Pat.

[Reza Sharifi]

Pat,

As I noted in the previous post, as long as both switches have the same exact IOS with the same feature set and the same exact license, it doesn't matter which switch is master and which one is member.  Remember the config is the same for ALL switches in the stack.  Look at the stack as one big switch, and of course what Leo noted regarding the master election is correct.

HTH

Reza

[Patrick McHenry]

Reza,

If I enter "reload" on this 2960 stack in cli, will it reload both switches at the same time?

Thanks, Pat.

[Reza Sharifi · Accepted solution]

That is correct.  Both switches will be rebooted.

HTH

[Patrick McHenry]

Thanks Reza

[Leo Laohoo]

So, you are saying that just because Switch 2 is the Master at the moment - it doesn't mean it will be the Master after reload. If I reload both at the same time the lower MAC will be the Master?

Hi Pat,

Good, I got you interested.  The answer is "NO".  The reason?  Because both switches have their priorities set to the default value of "1".

Let's say I want switch #2 as the Master and switch #1 as my Slave and secondary Master.

So what I would do is enter the following configuration lines:

conf t

switch 2 priority 15

switch 1 priority 13

end

wr

reboot

Now a switch with priority value of "15" means it will not attempt to join a Master election process (and subsequently shaves about 20 seconds during bootup time) and will become the Master.

Let's presume you reboot the entire stack.  Because of the lines above, switch #2 will become the Master immediately.  Switch #1 will go into the Master election process but says, "Hold on, someone (switch 2) has just announced to be the master.  In that case, I don't need to continue to the election process.  I'll be the slave instead."

At the end of the day, it doesn't matter which switch is the Master/Slave because the members of the entire switch stack share the same configuration.  This is one of the main benefits of Stacking.  Another benefit is redundancy.

Does this help?

[dynamitec1]

leola got it right.

1       Member b414.8938.2800     1      1       Ready

*2       Master b414.8938.3c80     1      1       Ready

But, I would do it slightly different.

conf t

switch 2 pri 15

switch 1 pri 13

switch 2 renum 1

switch 1 renum 2

exit

wr

reload

renumber will not take effect until devices are reloaded. So, the next time you do a "sh sw," it will display:

*1       Master b414.8938.3c80     15       Ready

2        Member b414.8938.2800     13       Ready

I'm just picky, I want the MASTER to be on #1 as well.  So, when I'm in the comm closet and trying to clean-up the cables, there's less room for error.

[Leo Laohoo]

I'm just picky, I want the MASTER to be on #1 as well.

Same here.