We are seeing an odd issue with a newly deployed Exchange 2016 in an Active-Active configuration. There are two sites, each with 2 Exchange servers. The DAG spans the 4 servers, with Active mailboxes at each site. We are using the Unbound namespace model, with the External URL being different than the Internal URL.
The issue is when a user attempts to connect to a mailbox that is hosted on the opposite site to what they are located. The connection is established, and the user is presented with the login dialog, then after logging in, the URL redirects to the External URL and the user is prompted for login again.
My initial thought was Exchange is incorrectly interpreting the connecting subnet as being outside of its subnet, so therefore external. From what I've read, Exchange is site-aware, so it should know that the other sites subnet is internal. We've checked the AD Sites and Services for any errors of misconfigurations, but the subnets are configured correctly.
nltest /server:<servername> /dsgetsite returns the correct site for each of the Exchange Servers.
So what could be causing the URL to redirect to the External one?
Best Answer
I am going to be blunt here. Your design and implementation is flawed.
Why are you using two different URLs? I haven't implemented that design for many years, because it confuses the end users and can cause more problems than it resolves.
Active/Active DAG rarely works in the way that most people think it does/should specifically if you lose the link between the two sites (which is the most common scenario) then one site will be down.
As you have four servers I would switch to two DAGs, one active server in each site. The other passive server acts as the FSW. Give each site its own URL, with the same URL being used internally and externally for all services (ActiveSync, Autodiscover (Which is AD site aware), EWS, OWA).
That is a design that is proven to work, is acceptable to end users and is best practise.