Catalyst 3750X Mixed Software Stack

[RICHARD MESSINGER]

Can someone please explain why the 3750X has the restriction where all of the members of the stack must be running the same software feature set whereas the older 3750E's do support a mixed feature set stack?

From the Managing Switch Stacks

http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst3750e_3560e/software/release/12.2_37_se/configuration/guide/swstack.html

A switch stack is a set of up to nine  stacking-capable switches connected through their StackWise Plus or  StackWise ports. You can connect only Catalyst 3750-E switches in a  stack, or you can connect both Catalyst 3750-E and Catalyst 3750  switches in the stack. Catalyst 3750-E stack members have StackWise Plus  ports, and Catalyst 3750 members have StackWise ports. The stack can  have one of these configurations:

•Homogeneous stack—A Catalyst 3750-E-only stack with only Catalyst 3750-E switches as stack members.

•Mixed stack

–A mixed hardware stack with Catalyst 3750-E and 3750 switches as stack members.

For example, a stack with Catalyst 3750-E and 3750 switches supporting the advanced IP services features.

–A mixed software stack with only Catalyst 3750-E switches supporting different features or  only Catalyst 3750 switches supporting different features as stack  members.

For example, a Catalyst 3750-E-only stack with some members running the  IP base feature set, other members running the IP services feature set,  and the remaining members running the advanced IP services feature set.

–A mixed hardware and software stack with the Catalyst 3750-E and 3750 switches supporting different features as stack members.

For example, a stack with the Catalyst 3750-E members running the  advanced IP services feature set and the Catalyst 3750 members running  the IP services software image.

But when it comes not to the new 3750Xwe have the following from

http://www.cisco.com/en/US/partner/prod/collateral/switches/ps5718/ps6406/data_sheet_c78-584733.html

The Cisco Catalyst 3750-X Series Switches with LAN  Base feature set can only stack with other Cisco Catalyst 3750-X Series  LAN Base switches. A mixed stack of LAN Base switch with IP Base or IP  Services features set is not supported.

Why the restriction and is that being addresses with a new software release?

[Fabienne Stephanoff]

Hello Richard,

It was always a recommendation.

According to this document:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps5023/prod_white_paper09186a00801b096a.html

Cisco IOS Software Images Must Be Identical

The Cisco StackWise technology requires that all units in the stack run the same release of Cisco IOS Software. When the stack is first built, it is recommended that all of the stack members have the same software feature set - either all IP Base or all IP Services. This is because later upgrades of Cisco IOS Software mandate that all the switches to be upgraded to the same version as the master.

With that being said I have seen customers run IP base with IP services even on a 3750x. LAN base will only run with LAN base though.

Cheers,

Fabienne.

[Leo Laohoo]

Can someone please explain why the 3750X has the restriction where all of the members of the stack must be running the same software feature set whereas the older 3750E's do support a mixed feature set stack?

Purely logical.

One of the reasons why Cisco developed this is because of redundancy.  If one stack member fails, the rest will go on without any disruptions.  So how does one accomplish this?  Well the switch stack has to run the same IOS version and the IOS feature set.

Because if you don't run the same IOS feature set and the stack master (which is running, for example, IP Services feature set) has all the routing configuration and FAILS, then the remainder of the stack takes over.  But if the remainder of the stack runs on a different feature set, for example IP Base only, how wil they "understand" what the commands are?