RocketMQ启动NameServer： 遇到org.apache.rocketmq.remoting.exception。RemotingConnectException:连接到本地主机：9876失败

org.apache.rocketmq.remoting.exception.RemotingConnectException: connect to localhost:9876 failed
	at org.apache.rocketmq.remoting.netty.NettyRemotingClient.invokeSync(NettyRemotingClient.java:394) ~[rocketmq-remoting-4.7.1.jar:4.7.1]
	at org.apache.rocketmq.broker.out.BrokerOuterAPI.registerBroker(BrokerOuterAPI.java:194) ~[rocketmq-broker-4.7.1.jar:4.7.1]
	at org.apache.rocketmq.broker.out.BrokerOuterAPI.access$000(BrokerOuterAPI.java:61) ~[rocketmq-broker-4.7.1.jar:4.7.1]
	at org.apache.rocketmq.broker.out.BrokerOuterAPI$1.run(BrokerOuterAPI.java:150) ~[rocketmq-broker-4.7.1.jar:4.7.1]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_221]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_221]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_221]
2022-10-05 20:13:16 WARN brokerOutApi_thread_3 - registerBroker Exception, localhost:9876
org.apache.rocketmq.remoting.exception.RemotingConnectException: connect to localhost:9876 failed
	at org.apache.rocketmq.remoting.netty.NettyRemotingClient.invokeSync(NettyRemotingClient.java:394) ~[rocketmq-remoting-4.7.1.jar:4.7.1]
	at org.apache.rocketmq.broker.out.BrokerOuterAPI.registerBroker(BrokerOuterAPI.java:194) ~[rocketmq-broker-4.7.1.jar:4.7.1]
	at org.apache.rocketmq.broker.out.BrokerOuterAPI.access$000(BrokerOuterAPI.java:61) ~[rocketmq-broker-4.7.1.jar:4.7.1]
	at org.apache.rocketmq.broker.out.BrokerOuterAPI$1.run(BrokerOuterAPI.java:150) ~[rocketmq-broker-4.7.1.jar:4.7.1]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_221]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_221]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_221]
2022-10-05 20:13:45 INFO BrokerControllerScheduledThread1 - dispatch behind commit log 0 bytes
2022-10-05 20:13:45 INFO BrokerControllerScheduledThread1 - Slave fall behind master: 215 bytes

解决办法：关闭防火墙
CentOS 7.0默认使用的是firewall作为防火墙
查看防火墙状态

firewall-cmd --state

停止firewall

systemctl stop firewalld.service

禁止firewall开机启动

systemctl disable firewalld.service