Stacking doubt regarding Master switch

[lap]

Hi all,

I explain the sitaution.

I have a customer which has a stack of 4 C3750G. Until 2 days ago member 1 switch in the stack was the master switch. Then cause of a power blackout member 1 switch which was the master went down and member 2 switch became the master.

My question is the following: When member 2 switch became the master did the other members in the stack (3,4) get reloaded? I am asking that because I read the following in a Cisco doc when adding a new master to an exiting stack:

Change the priority value of the switch to be added to a value  greater than the highest priority of the stack.

switch stack-member-number priority new-priority-value

Make sure that the stack is fully connected so that, when you connect the new switch, the stack will be at least in half connectivity, and do not partition.

With the new switch powered on, connect the StackWise ports of the switch to the stack.

The election for the stack master occurs, and the new switch will be  elected as the master since it has the highest priority value.

The members of the previous stack will reboot themselves to join the  new stack. After all the members come up, issue the command show switch to verify stack membership.

The customer has now received a new switch which I have added into the stack. What I did is to increase the priority of member 2 to 10 as it was set to 1 to make sure that the new switch will not become the master. But what would have happened if the new switch had a higher priority than the current master switch (member 2) ? Will all the stack member have rebooted?

Right now after adding the new switch member 2 is still master. But should I reboot member 2 so the other switches can join the stack?

What is the purpose of the master switch?

Thanks for hepling.

Best regards,

Laurent

[IAN WHITMORE]

Well I think the answer to your question is 'yes' they would have rebooted. I think you prbably read this document:

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a00807811ad.shtml

It says the advantages of a master switch are:

• System-level (global) features that apply to all stack members

• Interface-level features for each stack member

You will have to decide whether or not it's worth it!

regards,

Ian

[lap]

Hi Ian,

Thanks for your post. That is strange that all stack has to reboot! What is the logic in this? Stacking isn't about failover?

I don´t understand why all the stack has to reboot?

Regards,

Laurent

[IAN WHITMORE]

Just one of those things. I guess it's so there are no config conflicts as it changes from one master to another or something like that.

[lap]

Hi Ian,

Guessing are good but not enough:-)

Anyone has a precise explanation?

Regards,

Laurent

[IAN WHITMORE]

Well this looks promising and kinda verifies what I was guessing

Using the Configuration Manager

The configuration manager is a Cisco IOS control program that runs on the stack master. The configuration manager performs these functions:

•Maintains the running and saved configuration files and distributes them from the stack master to the member switches. The complete stack entity has one saved and one running configuration. All the switches in the stack use the stack-master running configuration.

•Keeps a copy of the startup and running configuration on all member switches. Any stack member can then become the new stack master.

•Synchronizes the running configuration to all member switches.

•When the stack master is powered off or rebooted, the newly elected stack master runs the configuration.

Using the Stack Manager

The Stack Manager is a Cisco IOS program that runs on the stack master switch and performs these tasks:

•Discovers other switches in the stack (stack members).

•Adds new switches to the stack after discovery.

•Removes a disconnected switch from the stack. The output of the show switch user EXEC command shows the switch as provisionedinstead of ready.

•Elects a stack master during stack boot-up or when you disconnect the working stack master from the stack.

•Resolves switch number conflicts when a new switch joins. Assigns a switch number and port numbers to the new switch and reboots it to effect the changes.

•Communicates with other switches by using stack messages and gathers and stores information from stack messages.

•Manages a stack merge when you connect two independent stacks into a single, larger stack. Renumbers some of the switches and selects one stack master.

Document:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/troubleshooting/switch_stacks.html