A logical approach to modernizing a legacy distributed control system is to do it in a phased manner, migrating a controller at a time. However, this creates a situation which must be addressed and planned for in any engineering and cutover strategy. In a recent analysis I performed on a Foxboro I/A system running a power plant, I discovered that 8% of the 11,000 connections in the logic configuration are controller Peer to Peer. How do you deal with these interactions between controllers? Are high level Unit statuses being communicated? Is control being performed peer to peer? Will a phased cutover plan require physical hardwiring between the old and new system to accommodate the peer to peer traffic? Consolidating controls into fewer controllers can help minimize the number of peer to peer connections that must be dealt with. It could be that a phased controller migration may not be possible because the controls are so highly distributed. These are just some of the things to consider when engineering and devising a cutover strategy for the modernization project. Running an analysis and knowing what the peer to peer connections are and planning for them will make for a more successful modernization project.