Cisco 3750 switch stack with different IOS images

ciscocisco-3750cisco-catalyststackingswitch

There is a situation here, I am trying to add a new switch to an exisiting stack and i found out that the switch image in my current stack and the new switch is different. Can i still go ahead and add the switch to the stack?

Exisiting Stack: sh version

Switch Ports Model              SW Version            SW Image
------ ----- -----              ----------            ----------
*    1 52    WS-C3750G-48PS     12.2(55)SE6           C3750-IPBASEK9-M
     2 52    WS-C3750-48P       12.2(55)SE6           C3750-IPBASEK9-M
     3 52    WS-C3750-48P       12.2(55)SE6           C3750-IPBASEK9-M
     4 52    WS-C3750-48P       12.2(55)SE6           C3750-IPBASEK9-M
     5 52    WS-C3750-48P       12.2(55)SE6           C3750-IPBASEK9-M
     6 52    WS-C3750-48P       12.2(55)SE6           C3750-IPBASEK9-M

New Switch: sh version

Switch Ports Model              SW Version            SW Image
------ ----- -----              ----------            ----------
*    1 52    WS-C3750-48P       12.2(55)SE10          C3750-IPSERVICESK9-M

Best Answer

You should really set the IOS version to be the same before adding a switch to the stack. Basically, the switches need to have the same stack protocol version, and only switches with the same IOS version are guaranteed to have that. Switches with the same major version numbers probably have the same stack protocol version, but that is not guaranteed. Having the same IOS version on a switch before adding it to a stack can save you problems.

Cisco has a very good document, which contains a full explanation about this:

Creation and Management of Catalyst 3750 Switch Stacks

Software Compatibility

Software compatibility between the stack members is determined by the Stack Protocol Version number. To view the stack protocol version of your switch stack, you can issue the show platform stack manager all command.

3750-Stk# show platform stack manager all
                                               Current
Switch#  Role      Mac Address     Priority     State
--------------------------------------------------------
 1       Slave     0016.4748.dc80     5         Ready
*2       Master    0016.9d59.db00     1         Ready

!--- part of output elided


                 Stack State Machine View
==============================================================

Switch   Master/   Mac Address          Version    Uptime   Current
Number   Slave                          (maj.min)            State
---------------------------------------------------------------------
1        Slave     0016.4748.dc80          1.11        8724    Ready
2        Master    0016.9d59.db00          1.11        8803    Ready

!--- rest of output elided

Switches with the same Cisco IOS software version have the same stack protocol version. Such switches are fully compatible, and all features function properly across the switch stack. Switches with the same Cisco IOS software version as the stack master immediately join the switch stack.

If an incompatibility exists, the fully functional stack members generate a system message that describes the cause of the incompatibility on the specific stack members. The stack master sends the message to all stack members.

Switches with different Cisco IOS software versions likely have different stack protocol versions. Switches with different major version numbers are incompatible and cannot exist in the same switch stack.

3750-Stk# show switch
                                               Current
Switch#  Role      Mac Address     Priority     State
--------------------------------------------------------
 1       Member    0015.c6f5.6000     1         Version Mismatch
*2       Master    0015.63f6.b700     15        Ready
 3       Member    0015.c6c1.3000     5         Ready

Switches with the same major version number but with a different minor version number as the stack master are considered partially compatible. When connected to a switch stack, a partially compatible switch enters version-mismatch (VM) mode and cannot join the stack as a fully functional member. The software detects the mismatched software and tries to upgrade (or downgrade) the switch in VM mode with the switch stack image or with a tar file image from the switch stack flash memory. The software uses the automatic upgrade (auto-upgrade) and the automatic advise (auto-advise) features.

The auto-upgrade occurs if the software release that runs on the stack master is compatible with the switch in VM mode and the tar file of the current image is available with any of the stack members. If tar file of the current image is not available, the auto-advise feature will recommend that a compatible image be downloaded with the required commands. The auto-upgrade and auto-advise features do not work if the switch master and switch in VM mode run different feature sets/packaging levels (IP services and IP base), but, from Cisco IOS Software Release 12.2(35)SE, auto-upgrade does support upgrades between cryptographic and non-cryptographic images of the same packaging level.

Note: If the auto upgrade does not work on the switch that shows the version mismatch error, use TFTP to manually upgrade the switch.

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