Migrating Stack Switches

vjcastigo · ‎10-26-2015

Hi Experts,

We are planning to replace our existing stack switches (WS-C3750-48TS x 4) with four new switches (WS-C3750X-48T-E x 4). Below are the main differences that I know of between the two models:

Current switches:

WS-C3750-48TS (fast Ethernet interfaces)
SW Version: 12.2(25)SEB4

New switches:

WS-C3750X-48T-E (gigabit Ethernet interfaces)
SW version: 15.0(1)SE3

With the above information, I would like to know if there are any default parameters that changed from IOS 12.2(25)SEB4 to 15.0(1)SE3? Our migration plan is to extract the current stack configuration, configure the new switches in a stack and apply the same config. Then we will remove the old stack and replace with the new stack switches in the rack. Also, do I need to consider the routers connected to the existing stack switch, such as their arp-table and etc?

I have attached the configuration of both stacks as well for your reference.

Thank you in advance!

Leo Laohoo · ‎10-26-2015

For stability purposes, use 12.2(55)SE10.

The old stack switch can support 12.2(55)SE10. I strongly recommend you upgrade the IOS of the existing switch stack before going to 3750X.

To upgrade, remove-and-replace each member of the stack one by one. This way you do not need to copy the configuration from one stack to another. Once the 3750X is joined to the existing stack of old 3750 the configuration gets copied across to the 3750X.

vjcastigo · ‎10-26-2015

Why do I need to upgrade the old stack to 12.2(55)SE10 if I am going to replace them with new stack that has higher IOS version?

Leo Laohoo · ‎10-26-2015

Why do I need to upgrade the old stack to 12.2(55)SE10 if I am going to replace them with new stack that has higher IOS version?

The following benefits happen if the existing stack gets upgraded:

1. The new 3750X can be added easily to the existing stack; and

2. Config gets verified with newer code.

vjcastigo · ‎10-26-2015

Hi Leo,

Thank you for the response. However, the new stack is on SW version: 15.0(1)SE3. Does it mean I have to downgrade it to 12.2(55)SE10 so I can add it to the old stack? And we do not plan to add the new switches to the old stack, instead we will replace them all. So the old stack will be removed from the rack, then we will replace it with a new stack.

Leo Laohoo · ‎10-26-2015

However, the new stack is on SW version: 15.0(1)SE3.

1. The current stack (non-3750G/E/X) cannot support this version: Not enough flash space.

2. 15.0(1) is a very unstable IOS.

Does it mean I have to downgrade it to 12.2(55)SE10 so I can add it to the old stack?

Yes. I also recommend the old stack to be loaded with 12.2(55)SE10 as well so a new 3750X, also running 12.2(55)SE10 can be added to the the old stack.

vjcastigo · ‎10-26-2015

We have a time constraint for the maintenance window as the impact is very high. Rack space is also an issue. Reason why we decided to completely replace the old stack with the new stack. With your recommendations, is it better to downgrade the new stack to 12.2(55)SE10 and then replace the old stack? Also, are there any changes in default parameters from one IOS version to another (e.g. qos default parameter, etc)?

Leo Laohoo · ‎10-26-2015

My favorite way of upgrading from a stack of 3750/G to a 3750X is this:

1. Upgrade the current stack to 12.2(55)SE10.

2. Ensure all new stack members (3750X) are running 12.2(55)SE10.

3. Remove stack member 3.

4. Insert one 3750X into current stack as stack member 3.

NOTE: When this happens, the 3750X will join the stack successfully and then copy the complete config from the current stack.

5. Remove stack member 2.

6. Insert one 3750X into current stack as stack member 2.

7. Remove stack member 1.

8. Insert one 3750X into current stack as stack member 1.

Now, compare the above process with the "traditional" one of powering off the existing stack and replacing all the the old stack with 3750X and then MANUALLY copy the configuration across.

vjcastigo · ‎10-26-2015

Thanks Leo. How about the change of default parameters? Does it actually happen in upgrading IOS version or the default parameters always stays the same?

Leo Laohoo · ‎10-26-2015

What "default parameters"? Please cite some examples.

vjcastigo · ‎10-26-2015

Like mls qos, arp table refresh, mac-address table refresh and etc.

Leo Laohoo · ‎10-26-2015

Nothing changes.