To enable dopd, you must add these lines to your /etc/ha.d/ha.cf file:

respawn hacluster /usr/lib/heartbeat/dopd 
apiauth dopd gid=haclient uid=hacluster

You may have to adjust dopd's path according to your preferred distribution. On some distributions and architectures, the correct path is /usr/lib64/heartbeat/dopd.

After having made this change and copied ha.cf to the peer node, you must run /etc/init.d/heartbeat reload to have Heartbeat re-read its configuration file. Afterwards, you should be able to verify that you now have a running dopd process.

	Note
	You can check for this process either by running ps ax | grep dopd or by issuing killall -0 dopd.

Then, add these items to your DRBD resource configuration:

resource resource {
    handlers {
        outdate-peer "/usr/lib/heartbeat/drbd-peer-outdater";
        ...
    }
    disk {
        fencing resource-only;
        ...
    }
    ...
}

As with dopd, your distribution may place the drbd-peer-outdater binary in /usr/lib64/heartbeat depending on your system architecture.

Finally, copy your drbd.conf to the peer node and issue drbdadm adjust resource to reconfigure your resource and reflect your changes.

To test whether your dopd setup is working correctly, interrupt the replication link of a configured and connected resource while Heartbeat services are running normally. You may do this by either physically unplugging the network link, or if that is not practical, by inserting a temporary iptables rule to drop incoming DRBD traffic.

	Caution
	This step is invasive; it affects all enabled DRBD resources, not just the one you are testing.

After this, you will be able to observe the resource connection state change from Connected to WFConnection. Allow a few seconds to pass, and you should see the disk state become Outdated/DUnknown. That is what dopd is responsible for.

Any attempt to switch the outdated resource to the primary role will fail after this.

When re-instituting network connectivity (either by plugging the physical link or by removing the temporary iptables rule you inserted previously), the connection state will change to Connected, and then promptly to SyncTarget (assuming changes occurred on the primary node during the network interruption). Then you will be able to observe a brief synchronization period, and finally, the previously outdated resource will be marked as UpToDate again.