What Happens When Replication Network Fails In Exchange 2010 DAG…
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…
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.
I need to disable failback as it floods my MAPI network between sites when the replication network goes down? Can it be done or should I just block the ports?
The switchover to MAPI network is by design, to not bring Exchange down just because you had a failure in replication network. Exchange is also designed to use a single NIC and hence you may need to look into the link between sites to see what kind of bandwidth is available.
What happens when the replication is up again? Does it automatically fail back from MAPI network to replication network?
It should. Not sure whether a restart of the service is required.
Dear Rajith Enchiparambil,
I’m not clear about heartbeat on MAPI or Replication Network. which network Exchange use to detect heartbeat?
Thanks in Adv.
Exchange creates a virtual IP NIC on the server when it is added to a the DAG/cluster, specifically for the reason of being strictly a heartbeat interface.
In my experience, if the replication network fails for some reason and MAPI picks up the “role” of replication, there is no automation for the DAG to go back to using the replication network. I’ve had to manually force the traffic back to the replication network, either by disabling/re-enabling the MAPI nic briefly (using virtual servers) or by rebooting.
That is exactly how it is designed to work. If your replication network goes down, it automatically moves the replication to the MAPI network, thus avoiding a system failure.
In the event of a failure affecting the Replication network, if the MAPI network is unaffected by the failure, log shipping and seeding operations will revert to use the MAPI network, even if the MAPI network has it’s ReplicationEnabled property set to False. When the failed Replication network is restored to health and ready to resume log shipping and seeding operations, you must manually switch over to the Replication network. To change replication from the MAPI network to a restored Replication network, you can either suspend and resume continuous replication by using the Suspend-MailboxDatabaseCopy and Resume-MailboxDatabaseCopy cmdlets, or restart the Microsoft Exchange Replication service. We recommend using the suspend and resume operations to avoid the brief outage caused by restarting the Microsoft Exchange Replication service.
Thanks again Josh.