DELL EMC Unity: Replication connection failed to validate after upgrading to code 5.1

- After the code upgrade to 5.1, the customer was able to resume all the replication sessions but the replication connection failed to validate.

A 09/04/21 21:57:35.448 DART_REP 106c0891 [NOTICE] Audit: The file system replication session rep_sess_res_1_res_6_CETVXXXXX_CETVXXXXXX in NAS server group replication session start successfully.
A 09/04/21 21:57:35.546 DART_REP 106c0891 [NOTICE] Audit: The NAS server replication session rep_sess_nas_1_nas_3_CETVXXXXXX_CETVXXXXXX in NAS server group replication session start successfully.
B 09/04/21 21:58:03.345 Health 60771 [INFO] User: Replication session rep_sess_res_1_res_6_CETVXXXXXX_CETVXXXXXX is operating normally
B 09/04/21 21:58:04.598 Health 60771 [INFO] User: Replication session rep_sess_nas_1_nas_3_CETVXXXXXX_CETVXXXXXX is operating normally

B 09/04/21 22:06:25.212 ReplicPlugin 610012 [ERROR] Audit: User local/admin failed to validate remote system connections RS_11.
B 09/04/21 22:06:25.251 Health 6077c [ERROR] User: The remote system connection failed to validate the replication interface connectivity between the two systems.

- The operational status for replication connection is "failed to validate" from GUI or uemcli output. 

2: ID = RS_11
Name = XXXXXXXXXX001
Address = xx.xx.xx.xx
Alternate Management Address = xx.xx.xx.xx
Model = Unity 400
Serial number = CETVXXXXXX
Connection type = async
Source interfaces = xx.xx.xx.xx, xx.xx.xx.xx
Local interfaces = xx.xx.xx.xx, xx.xx.xx.xx
Remote interfaces = xx.xx.xx.xx, xx.xx.xx.xx 
Operational status = Failed To Validate (0x840c) <<<<<<<<<<<<<<<
Health state = Minor failure (15)
Health details = "One or more replication interface pairs are experiencing network connectivity issues between the local and remote systems. (https://xx.xx.xx.xx/help/webhelp/en_US/index.html?#unity_t_replication_session_cannot_communicate_with_the_system.html [xx.xx.xx.xx]"
Synchronous FC ports =
Bandwidth schedules = uses available bandwidth
Current bandwidth = uses available bandwidth

Note: 
The customer is able to pause/resume existing replication sessions or even create a new replication session, the data transferring of replication sessions appear to be working properly. 

- From cemtracer_dataprotection.log, validation failed due to unable to ping target replication interface. 

06 Sep 2021 02:24:29 - [DataProtectionStorageModel] ERROR -

{0:107288:261867001}
[13347|17923|f6c7ab40][operator() @ ../../../components/providers/osls/common/DataProtection/StorageModel/impl/ResourceReplicationSessionImpl.h:589] Ping failed: local ip: xx.xx.xx.xx
06 Sep 2021 02:24:29 - [DataProtectionStorageModel] ERROR -

{0:107288:295460565}
[13347|17922|f66feb40][operator() @ ../../../components/providers/osls/common/DataProtection/StorageModel/impl/ResourceReplicationSessionImpl.h:589] Ping failed: local ip: xx.xx.xx.xx
06 Sep 2021 02:24:30 - [DataProtectionStorageModel] ERROR -

{0:107288:402286177}
[13347|17924|f6c9bb40][operator() @ ../../../components/providers/osls/common/DataProtection/StorageModel/impl/ResourceReplicationSessionImpl.h:589] Ping failed: local ip: xx.xx.xx.xx
06 Sep 2021 02:24:30 - [DataProtectionStorageModel] ERROR -

{0:107288:408068717}
[13347|17925|f6cbcb40][operator() @ ../../../components/providers/osls/common/DataProtection/StorageModel/impl/ResourceReplicationSessionImpl.h:589] Ping failed: local ip: xx.xx.xx.xx

- Engineering has confirmed ping is a new verification added to replication connection in OE version 5.1

In this case, the customer has confirmed they did disable ICMP in their environment. It's not a code bug and will only have the issue in an ICMP-disabled environment. 

An option is added in 5.2 by Development team to revert to the old non-ping mode for replication validation to work in an ICMP-disabled environment. Customer may use below uemcli command to turn "remoteSysInterfaceAutoPair" parameter off on either of the two arrays. This parameter is turned on by default.
service@Unity spb:~/user# uemcli -u admin -p xxxxxxxx /sys/general set -remoteSysInterfaceAutoPair off
Operation completed successfully.

service@Unity spb:~/user# uemcli -u admin -p xxxxxxxx /sys/general show -detail
1:    System name                               = Unity
      Model                                     = Unity 680
      UUID base                                 = 0
      Product serial number                     = CKMxxxxxxxxxxx
      Auto failback                             = on
      Health state                              = OK (5)
      Health details                            = "The system is operating normally."
      Power (Present)                           = 570 watts
      Power (Rolling Average)                   = 572 watts
      Supported SP upgrades                     = SP880
      Remote system interface automatic pairing = off<<<<<

If customer cannot upgrade the code to 5.2 yet, customers can re-enable ICMP in their environment for the replication interface pairs if allowed by their environment.