Is there an easy migration process to migrate the config or do I have to understand what the current network is configured as and build a new config for the new topology.
You really need to understand how the current network is configured before you can do the upgrade otherwise if something doesn't work you will have no idea of where to begin troubleshooting.
That doesn't mean you need to build an entirely new configuration because you may well be able to apply most of the configuration on your existing switches to the new switches although it's not clear what functions the new switches will be doing ie.
currently you have a stack of 3750s doing what ? eg. access for users, routing for vlans etc.
you are replacing them with 3750x's switches and 4500x switches so are you splitting up the functions of the 3750s between them.
If you are then obviously you cannot take the existing configuration and copy it to both the 3750x and the 4500x switches.
When I did upgrades like this I would download the existing configurations to my laptop and make any necessary edits. If I couldn't use the existing configuration I just created new ones. When I came to upgrade I had all the configurations ready to load onto the switches.
Bear in mind that some configuration just won't copy across ie. if you have QOS on your current switches and you try to copy that to the 4500x it probably wont work as they use different commands for a lot of the same functions.
But the key thing is you must understand what you are trying to do ie. simply trying to copy across configurations without the understanding could create a lot of problems.
Jon
