To be able to replicate data from DD3 to DD2, the Distribution Server name needs to get the Mode DD2 and type in the port number for the DD2 Service.
If you have an older version of LS Retail NAV that does not include this form, you can type in the Distribution Server field: STORE3:16750:DDOLD
When replicating from DD2 host to DD3 host, nothing needs to be set up in the Distribution Location card for the DD3 locations. Both will only include the Host name, no port information or connection property information, unless any of the DD is not running on the default port.
Where is my Transaction Server?
DD3 supports Transaction Server Requests, so if you were upgrading from a DD2 setup at HO, you can tell DD3 to accept incoming connection on the ports used before by the Transaction Servers. If there were more than one TS Services running, add all ports for all previous TS in the Data Ports field.
In NAV setup you just use the setup like before to point to the TS Distribution Location host, or use the default Distribution Location card, used for normal replication. Both will work as DD3 will accept both types of requests.