3750 StackWise Connection

Answered Question
Mar 22nd, 2007
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I have a question with regards to Master assignment on a grouping of (4) 3750 Switches connected via Stackwise


Take the scenario with 4 x 3750 switches where three of them are IP Base (SMI) and one is IP Services (EMI) and the stack is configured with the IP Services switch as the Master.


1) If Power is lost to the stack and they all reboot at the same time is there a configuration to ensure that the IP Services switch continues to be the master ?


2) Am I also right in saying that the master switch dictates what IOS the other switches download and use


3) If the above is accurate then does the SMI switch (which has downloaded a EMI ver) revert back to the original IOS if the EMI master fails?


If the above could be clarified then there will definatly be a 5 rating handed out :)


Thanks

Correct Answer by ankbhasi about 10 years 1 month ago

Hi Nathan,


If you have a stack of SMI switches, with a single EMI unit, the EMI unit will, by default, become the master switch. It will give EMI functionality to the entire stack. This is because Layer-3 functionality is centralized in nature, on the 3750. However, if the master switch were to fail, the entire stack would revert to the feature-set of the new master, who happens to be SMI. The user would lose all EMI-only functionality such as advanced IP routing protocols. This is the reason we include a recommendation that if users deploy a mixed stack, they should have at least two EMI units to provide protection against such failures.


If power is lost to the stack and they all reboot at the same time and also come up at a same time EMI switch will always become a master because the EMI has precedence over the SMI during stack master election, assuming that the priority value of the stack members are the same.


But incase EMI switch boots up later and SMI switch comes up first EMI switch does not automatically become the stack master. If you want the EMI switch to become the stack master, reset the current SMI stack master by using the reload slot stack-member-number privileged EXEC command. The EMI switch is elected the stack master, assuming its priority value is higher or the same as the other stack members.


HTH


Ankur



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Correct Answer
ankbhasi Thu, 03/22/2007 - 04:24
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  • Cisco Employee,

Hi Nathan,


If you have a stack of SMI switches, with a single EMI unit, the EMI unit will, by default, become the master switch. It will give EMI functionality to the entire stack. This is because Layer-3 functionality is centralized in nature, on the 3750. However, if the master switch were to fail, the entire stack would revert to the feature-set of the new master, who happens to be SMI. The user would lose all EMI-only functionality such as advanced IP routing protocols. This is the reason we include a recommendation that if users deploy a mixed stack, they should have at least two EMI units to provide protection against such failures.


If power is lost to the stack and they all reboot at the same time and also come up at a same time EMI switch will always become a master because the EMI has precedence over the SMI during stack master election, assuming that the priority value of the stack members are the same.


But incase EMI switch boots up later and SMI switch comes up first EMI switch does not automatically become the stack master. If you want the EMI switch to become the stack master, reset the current SMI stack master by using the reload slot stack-member-number privileged EXEC command. The EMI switch is elected the stack master, assuming its priority value is higher or the same as the other stack members.


HTH


Ankur



glen.grant Thu, 03/22/2007 - 05:37
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the easiest way to guard gainst this is to download the EMI software out of the stackmaster bootflash down to the other switches bootflash: and add a boot system switch all command so that it boots off that image even if the stackmaster dies.

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