APC-Pwerchute Network Shutdown Service unreachable due to filtering

We (NW60-SP5 + BM36) installed the service for gracefully
shutting down the server while the UPS (192.168.xxx.5) runs
out of energy and this shutdown-service on the
bordermanager-server (192.168.xxx.3 private ip-address on
the private nic) has a communication-problem with the UPS.

From my vision (set tcp debug = 1) the following describes
the problem (ping works, rest does not):

RECEIVE:pktid:256 192.168.xxx.5->192.168.xxx.3 ttl:64
(ICMP)Echo Request
LOCAL:pktid:256 192.168.xxx.5->192.168.xxx.3 ttl:64
(ICMP)Echo Request
TRANSMIT:pktid:35060 192.168.xxx.3->192.168.xxx.5 ttl:128
(ICMP)Echo Reply

RECEIVE:pktid:42304 192.168.xxx.5->192.168.xxx.255 ttl:64
(UDP)
UDP:Source Port:37078Destination Port:3052

LOCAL:pktid:42304 192.168.xxx.5->192.168.xxx.255 ttl:64
(UDP)
UDP:Source Port:37078Destination Port:3052

Discard Incoming: cause(FILTERING), reason(5)

When disabling filtering it works fine. But I do not see
what filter-exception I have to set up for the privat nic or
the private ip-address.

Any hint is highly appreciated.

Sincerely

Karl