Why broker log continuous throws error about 'amq shutting down NC' when networkConnectors are used?

問題

I have a Master/Slave AMQ setup with shared NFS folder for KahaDB storage. When I start the server, the server logs continuous throw below errors:

2019-09-19 09:30:45,175 | INFO  | iveMQ Task-14848 | DiscoveryNetworkConnector        | etwork.DiscoveryNetworkConnector  120 | 162 - org.apache.activemq.activemq-osgi - 5.11.0.redhat-630283 | Establishing network connection from vm://amq to tcp://<backup AMQ server IP address>:61616
2019-09-19 09:30:45,177 | INFO  | e[amq] Task-5816 | DemandForwardingBridgeSupport    | rk.DemandForwardingBridgeSupport 1067 | 162 - org.apache.activemq.activemq-osgi - 5.11.0.redhat-630283 | amq Shutting down NC
2019-09-19 09:30:45,178 | INFO  | e[amq] Task-5816 | DemandForwardingBridgeSupport    | rk.DemandForwardingBridgeSupport  321 | 162 - org.apache.activemq.activemq-osgi - 5.11.0.redhat-630283 | amq bridge to Unknown stopped
2019-09-19 09:30:45,179 | WARN  | iveMQ Task-14848 | DiscoveryNetworkConnector        | etwork.DiscoveryNetworkConnector  165 | 162 - org.apache.activemq.activemq-osgi - 5.11.0.redhat-630283 | Could not start network bridge between: vm://amq and: tcp://<backup AMQ server IP address>:61616 due to: Connection refused