We have a customer that needed to migrate from Exchange 2010 to Exchange 2013 and keep the old ip-address in place for smtp traffic from inside and outside.

In clustered Exchange 2010 and 2013 the Primary Active Manager has the clustered role and the quorum.

So therefore we can assign i single ip-address to the clusterd role (DAG) and make that connection point for SMTP and client access traffic.

Https traffic come to a different ip-address.

And a picture to tell it all