Connection Types
Full Bandwidth Connection
This illustration shows an example of a stack of Catalyst 3750 switches that provides full bandwidth and redundant StackWise cable connections:
When a cable fails at a single place, the stack will run with the half bandwidth connection.
In order to find the stack-ports through which the switches are connected to the stack, issue the show switch stack-ports command.
3750-Stk#show switch stack-ports
Switch # Port 1 Port 2
-------- ------ ------
1 Ok Ok
2 Ok Ok
3 Ok Ok
Alternatively, in order to find the nearby switch on each port, issue the show switch neighbors command.
3750-Stk# show switch neighbors
Switch # Port 1 Port 2
-------- ------ ------
1 2 3
2 1 3
3 2 1
This illustration shows a stack of Cisco EtherSwitch service modules and Catalyst 3750 switches that provides full bandwidth and redundant connections:
Half Bandwidth Connection
This illustration shows an example of a stack of Catalyst 3750 switches with incomplete StackWise cable connections. This stack provides only half bandwidth and does not have redundant connections:
When a cable fails at a single place, the stack will be partitioned into two stacks.
3750-Stk# show switch stack-ports
Switch # Port 1 Port 2
-------- ------ ------
1 Ok Down
2 Ok Ok
3 Ok Down
3750-Stk# show switch neighbors
Switch # Port 1 Port 2
-------- ------ ------
1 2 None
2 1 3
3 2 None
Creation and Management of Cisco Catalyst 3750 Stacks
The stack member number (1 to 9) identifies each member in the switch stack. The member number also determines the interface-level configuration that a stack member uses. You can display the stack member number if you use the show switch user EXEC mode command.
3750-Stk>show switch
Current
Switch# Role Mac Address Priority State
--------------------------------------------------------
1 Slave 0016.4748.dc80 5 Ready
*2 Master 0016.9d59.db00 1 ReadyPriority Values
A higher priority value for a stack member increases its likelihood to be elected stack master and to retain its stack member number. The priority value can be 1 to 15. The default priority value is 1. You can display the stack member priority value with the show switch user EXEC mode command.
3750-Stk>show switch
Current
Switch# Role Mac Address Priority State
--------------------------------------------------------
1 Slave 0016.4748.dc80 1 Ready
*2 Master 0016.9d59.db00 5 ReadyHow do you change the priority value?
From the global configuration mode, issue the command switch stack-member-number priority new-priority-value .
From the bootloader switch: prompt, issue the command set SWITCH_PRIORITY new-priority-value .
Hardware Compatibility
The Cisco Catalyst 3750 series switches use Switch Database Management (SDM) templates to optimize the system resources for specific features dependent on how the switch is used in the network. There are two versions of the SDM templates: Desktop and Aggregator. The 3750-12S switch alone supports both templates. All other model switches of the 3750 series support only the Desktop version.
When a Cisco Catalyst 3750 switch stack consists of 3750-12S and other models, make sure to use only the Desktop SDM template. This is an output from the show switch command when an SDM mismatch exists:
3750-Stk# show switch
Current
Switch# Role Mac Address Priority State
------------------------------------------------------------
*2 Master 000a.fdfd.0100 5 Ready
4 Member 0003.fd63.9c00 5 SDM MismatchTo change the SDM template on a 3750-12S to Desktop version, complete these steps:
3750-Stk# conf t
3750-Stk(config)# sdm prefer routing desktop
3750-Stk(config)# exit
3750-Stk# reloadFor more information on the SDM templates, refer to Configuring SDM Templates.
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 ReadySwitches 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.
Create a Switch Stack from Two Stand-alone Stacks
This example shows how a switch stack is created from two stand-alone stacks.
Switch-A and Switch-B are merged together to form the stack.
and
A stack-master election occurs between Switch-A and Switch-B; let us consider that Switch-B wins.
Switch-A will reload itself and join the switch stack.
The stack member number of Switch-A will change since it conflicts with Switch-B. Switch-A will choose the lowest available stack number, which in this case, is number "2".
Create a Switch Stack from Two Two-member Stacks
This example shows how two switch stacks merge to form a stack.
The first switch stack consists of two members: Switch-A and Switch-B.
The second switch stack consists of members Switch-C and Switch-D with Switch-C as the stack master.
When these two switch stacks are merged together, the election for stack master occurs; let us consider that Switch-B wins the election.
Switch-A will retain its stack member number.
Switch-C and Switch-D will reload themselves and join the stack with new stack member numbers of "3" and "4" respectively.
