Recently when helping a customer with a ConfigMgr 2007 to 2012 R2 upgrade and migration, we were planning to upgrade their secondary sites to standard DPs. When setting up ConfigMgr 2012 R2 migration tools in the console, none of secondary sites were showing as being available for DP sharing. In reviewing the site’s migctrl.log file, there was an entry for an error that stated “The DP is NOT eligible for sharing because no ports between the legacy site and the current site are the same.”
In this case, the customer had configured the 2007 primary site to have clients communicate on a custom port, and not use the standard default port 80, of which the 2012 primary site was configured to use.
By changing 2012 to also use that same custom port, re-running the source hierarchy gathering process, the migration tool (and migctrl.log) now displayed the secondary site servers available for upgrade.