Hello Ray,
We , both are in same boat . We have a Automation Network which is a Layer-2 and Flat Network and we are going to migrate to Routed L3 Network with Vlan's (6509 will be core)which will happen by end of this month.
As per our Project Plan , we will introduce New Cisco devices with default Vlan and all the ports will be Vlan1 .There will be single connectivity (Gigabit) from New Network to old Network which is a FDDI Network sothat New Network will communicate with old Network in through Vlan1 .We are going for single link between (1000Base-SX ) both the Networks since old Network does not support "Ether Channel " or OSPF for load balancing . The above plan is Phase-1 .
In phase-2 , the plan is to move less critical resources (not servers ) to New Network and observe for sometime and move critical resources later .In phase-2 , we will introduce New IP address scheme with L3 Vlan's and move each area to New Network and obiviously we need to change the IP address, mask and introduce the Gateway for the Hosts who got migrated to New Network with L3 Vlan(s) .These new Layer-3 Vlan's will talk to Vlan1 through Routing engine and to Old Network also since Old Network also will be same Vlan1 . Fortunately , we don't have any WAN links . It's purely Campus Network with Automation devices connected.
This is our Plan and I have to see how it goes !
Regards,
Raju
