3750 switch Stack Issue

[simon clarke]

HI All 

I attended a fault call today in which switch 4 had failed in a 4 switch stack of 24 port 3750 2U switches, i was sent a 48 port 3750 1u switch, i prepared this switch with the correct ios to match the rest of the stack configured vtp as server mode as it was the core switch stack and this is what the customer wanted. 

once i introduced it back into the stack in took the switch 4 place copied over the vlans but did not configure the interfaces at all which i had to do manually as they were trunk ports into a VM enviroment it was tense for 5 minutes.

My question is would it have been because i did not provision the switch that it did not pull down the interface config ?

Is it becuase it was a 48 port and not a 24 port ?

is it a potential ios bug?

Thanks In Advance 

Simon 

[Mark Malone]

Hi

you configure it first before adding it to a stack or as you did just wait and then configure it , same for 38 and 37s stacks

http://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_01100101.html

Offline Configuration to Provision a Stack Member

You can use the offline configuration feature to provision (to supply a configuration to) a new switch before it joins the switch stack. You can configure the stack member number, the switch type, and the interfaces associated with a switch that is not currently part of the stack. The configuration that you create on the switch stack is called the provisioned configuration. The switch that is added to the switch stack and that receives this configuration is called the provisioned switch.

You manually create the provisioned configuration through the switch stack-member-number provision type global configuration command. The provisioned configuration is automatically created when a switch is added to a switch stack and when no provisioned configuration exists. When you configure the interfaces associated with a provisioned switch (for example, as part of a VLAN), the switch stack accepts the configuration, and the information appears in the running configuration. The interface associated with the provisioned switch is not active, operates as if it is administratively shut down, and the no shutdown interface configuration command does not return it to active service. The interface associated with the provisioned switch does not appear in the display of the specific feature; for example, it does not appear in the show vlan user EXEC command output.

The switch stack retains the provisioned configuration in the running configuration whether or not the provisioned switch is part of the stack. You can save the provisioned configuration to the startup configuration file by entering the copy running-config startup-config privileged EXEC command. The startup configuration file ensures that the switch stack can reload and can use the saved information whether or not the provisioned switch is part of the switch stack.

• Effects of Adding a Provisioned Switch to a Switch Stack
• Effects of Replacing a Provisioned Switch in a Switch Stack
• Effects of Removing a Provisioned Switch from a Switch Stack

[simon clarke]

HI Mark 

Thanks for taking the time to reply, so either way i would have had to manually configure the interfaces on the replacement switch whether i did it before connecting to the stack or after ?

I was just slightly confused as i thought the stack master would provide this ?

Thanks 

Simon 

[Mark Malone · Accepted solution]

Well from experience on stacks I have always configured them or copied the config back in from flash master to running config to overwrite new ports with config that was taken before crash , I haven't seen it where the master replaced the config on new switch port just by adding a new switch, if the config is in startup you can do .......more flash:startup-config  , this will allow you see the previous port config and copy it over and then save it

Really your worried about the 5 minutes it took to configure get them back online , I know the feeling :)  I would be saying to the customer though why were these critical servers physical or VM not dual homed to say switch 1 and 4 so when there is an outage like that again there not down at all , just loss of resiliency and a bit of throughput , critical systems should be dual connections to avoid this issue always

[simon clarke]

Thanks mark your right it was a tense few minutes!!  just so i fully understand when the switch 4 failed and had to be removed from the stack the configuration for it remained in running memory.

so i configured the new blank switch with the same ios version so it will integrate with the stack and changed the vtp to server at the customers request, at this point i should have configured it ( provisioned) it as switch 4 and then put a full copy of the config file which i would get off the stack master ?

Alternatively i could have just reintroduced it into the stack blank with the correct ios version the running config would recognize it as the missing switch 4 and at this point i would just need to hook up to the console or get an ssh/telnet connection from the internal network and copy the config from the flash of the stack master to the running config of the replaced switch 4 ?

Thanks for the help i just wanted to make sure i fully understand. I agree about the dual homing god only knows why he hadn't implemented that 

thanks 

Simon 

[Mark Malone]

I think its removed from running config as switch is removed but full config should still be in startup file still,  if it was not saved as that would copy In the new config with the ports removed to the startup file so you wouldnt be able to copy that in and would have to get a previous saved copy of the config to get the old port config of failed switch

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so i configured the new blank switch with the same ios version so it will integrate with the stack and changed the vtp to server at the customers request, at this point i should have configured it ( provisioned) it as switch 4 and then put a full copy of the config file which i would get off the stack master ?

You could copy the full config from a file in flash whether its the startup that still has the full config or just a saved archive but always check that file first make sure ports all align and nothings missing thats in current config , use the more command this allows you to read the whole file before copying it into running config , you can read any txt or cfg file that's in flash with it go through the config and check it

or just use more command and copy in the port config that you need manually to the new switch ports that are blank in running config

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Alternatively i could have just reintroduced it into the stack blank with the correct ios version the running config would recognize it as the missing switch 4 and at this point i would just need to hook up to the console or get an ssh/telnet connection from the internal network and copy the config from the flash of the stack master to the running config of the replaced switch 4 ?

Yes you can do that too again though always check the file first just to be sure