EEM Replication between two nodes works only one direction

Document ID : KB000075096
Last Modified Date : 30/03/2018
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Issue:
We have an existing SOI r4.0.2 environment with EEM 12.51.3.14. There are two EEM servers configured with multiwrite replication. This current environment has been working fine for the past year. However, we just noticed that the multiwrite updates quit working in both directions and about a week ago started failing in one direction but ok in the other. In reviewing log files. For the one EEM server which currently can't be updated from the other, in the itechpoz_warn log file I find messages like: WARN : Remote DSA '<EEM server name>' failed address check The server named in that message seems not able to update the server which has these log messages. Is there something that explains how this address check is failing, and is that the cause of my problem?
 
Cause:
In the itechpoz_warn_<date>.log found the following message
[168] 20180320.160609.422 WARN : Remote DSA 'itechpoz-<EEM server name>' failed address check
It appears that the firewall is changing the source IP Address of the packets from one of the EEM servers. So it's not blocking, the one EEM server is not recognizing them.
Resolution:
It turns out that a change in a firewall caused the firewall to NAT the IP address of the one EEM server. It was not a case of blocking ports. So the packets arriving had a source IP address of the firewall and not of the EEM peer server. As a result EEM did not recognize the updates because it was a request seeming to originate from an unknown server.