Unable to manage MDM devices after ZCM 2020 upgrade

ZCM Zone upgraded to 2020, once upgraded no iPads could be managed or deployed.
MDM (Mobile Device Management) server was in a DMZ.


Error seen in loader-messages.log:

Caused by: org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss for /DeviceSyncType/c9d824a849227b40ad6e0d7483bba8f1
 at org.apache.zookeeper.KeeperException.create(KeeperException.java:99)
 at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
 at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:1102)
 at org.apache.curator.framework.imps.ExistsBuilderImpl$3.call(ExistsBuilderImpl.java:268)
 at org.apache.curator.framework.imps.ExistsBuilderImpl$3.call(ExistsBuilderImpl.java:257)
 at org.apache.curator.connection.StandardConnectionHandlingPolicy.callWithRetry(StandardConnectionHandlingPolicy.java:64)
 at org.apache.curator.RetryLoop.callWithRetry(RetryLoop.java:100)
 at org.apache.curator.framework.imps.ExistsBuilderImpl.pathInForegroundStandard(ExistsBuilderImpl.java:254)
 at org.apache.curator.framework.imps.ExistsBuilderImpl.pathInForeground(ExistsBuilderImpl.java:247)
 at org.apache.curator.framework.imps.ExistsBuilderImpl.forPath(ExistsBuilderImpl.java:206)
 at org.apache.curator.framework.imps.ExistsBuilderImpl.forPath(ExistsBuilderImpl.java:35)
 at com.novell.zenworks.zookeeperclient.curator.ZookeeperClient.exists(ZookeeperClient.java:421)

Resolved by opening the zookeeper ports 6789, 6790 and 6791 between a primary on the network and primary in the DMZ.
ZENworks 2020 TCP and UDP Ports
https://www.novell.com/documentation/zenworks-2020/zen_ports/data/zen_ports.html