MySQL Client can Connect but Replication Slave Can't We have an odd issue we've never come across. We have roughly 14 pairs of master/slaves all running MySQL 5.6.35 without issue. We are trying to add a slave to a slave (which we have two other instances of running in other data centers). We can connect from the command line of the new backup DB (slave) server as follows:
[root@BackupDB ~]# mysql -u slave -p -h xx.xx.xx.xx

Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 47075
Server version: 5.6.35-log MySQL Community Server (GPL)

mysql xx.xx.xx.xx:3306 &lt;(none)&gt;

However when the slave attempts to connect we get the following status:
mysql localhost:mysql.sock &lt;(none)&gt; show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Connecting to master
                  Master_Host: xx.xx.xx.xx
                  Master_User: slave
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: bin.000001
          Read_Master_Log_Pos: 4
               Relay_Log_File: relay.000002
                Relay_Log_Pos: 4
        Relay_Master_Log_File: bin.000001
             Slave_IO_Running: Connecting
            Slave_SQL_Running: Yes
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 120
              Relay_Log_Space: 120
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 2003
                Last_IO_Error: error connecting to master 'slave@xx.xx.xx.xx:3306' - retry-time: 60  retries: 32
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 0
                  Master_UUID: 
             Master_Info_File: /var/lib/mysql/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 200922 16:06:29
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 
                Auto_Position: 0
1 row in set (0.00 sec)

We have verified that the slave user has SLAVE REPLICATION privileges on the master as follows:
grant replication slave on *.* TO 'slave'@'xx.xx.xx.xx' identified by 'xxxxx';
flush privileges

We have set the master information on the slave as follows:
change master to master_host='xx.xx.xx.xx', master_port=3306, master_user='slave', master_password='abc', master_log_file='bin.000001', master_log_pos=0;

For the purposes of this exercise we have made the password &quot;abc&quot; to avoid a fat-finger situation. We have had two people double-check that the IP address, ports and passwords were the same.
We are stumped and any help would be appreciated.
A 2003 error is normally some form of connectivity error, you may want to check firewall settings, routing and SELinux status.
For the latter, you can either go and fix the SELinux permissions properly but as a quick and dirty test you can do the following
sudo setenforce 0

Hope the above helps.