I have mentioned in my previous article as to how to collapse the DAG networks and configure replication, read here. The correct way as explained in the article is to disable replication on the MAPI network and enable it on the replication network. But, what happens when the replication network fails for some reason? Does Exchange start queuing up the log files?
Exchange Team has thought about it and the way it works is that if the replication network goes down for some reason, Exchange starts using the MAPI network for replication. There are no popups when this happens, maybe an entry is created in the application log. That’s it. As Exchange maintains the flipping of networks for routing replication traffic, things work as normal.
But, what happens if you have disabled replication on the MAPI network as per the article mentioned above? It is a checkbox on the DAG properties to turn it on, but it is not necessary that an exchange admin picks up the failure immediately (he/she should).
Luckily, the algorithm used by Exchange takes care of this situation as well. If the replication network fails for some reason and replication is turned off on the MAPI network, Exchange will still go ahead and use the MAPI network for replication. Even though it is coded to function in this manner, you still need to disable replication on the MAPI network, so that Exchange uses the replication network in the first place.