Changing IP of all domain controllers in a forest

Hi,

I have set up an AD forest comprising of 30 domain controllers with replications for each domain controller.

They had been set up a year ago and have been running smoothly.Each domain controller is a windows 2012 R2 box and has its own DNS.

A requirement has come now which needs to me to change the IP of all the domain controllers in the forest.And I am truly at a loss here because I have no idea how and where to start in a forest so big.

Demoting a domain controller and adding it back is a tough option because  I tried it once while setting the forest up and it was a terrible experience.

Any suggestions or help will be much much appreciated.