Configured MySQL replication but its not working I have configured MySQL master and slave replication setup on 5.5.x.
But for some reason data is not getting replicated properly. What might be the reason?

At Master:

/etc/my.cnf

[mysqld]
log-bin=/var/lib/mysql/mysql-bin.log
server-id=1
innodb_flush_log_at_trx_commit=1
sync_binlog=1
binlog-do-db=cmdb
binlog-do-db=nagios


mysql> show master status;

+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000005 |   168019 | cmdb,nagios  |                  |
+------------------+----------+--------------+------------------+


At Slave:

/etc/my.cnf

[mysqld]
server-id=2
log-bin=/var/lib/mysql/mysql-bin.log
innodb_flush_log_at_trx_commit=1
sync_binlog=1
report-host=10.10.0.22
replicate-do-db=cmdb
replicate-do-db=nagios


mysql>  show slave status\G;

*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 10.10.0.21
                  Master_User: replicator
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000005
          Read_Master_Log_Pos: 198123
               Relay_Log_File: CentOS62-relay-bin.000012
                Relay_Log_Pos: 198269
        Relay_Master_Log_File: mysql-bin.000005
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB: cmdb,nagios
          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: 198123
              Relay_Log_Space: 198574
              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: 0
                Last_IO_Error:
               Last_SQL_Errno: 0
               Last_SQL_Error:
  Replicate_Ignore_Server_Ids:
             Master_Server_Id: 1
1 row in set (0.00 sec)
What concerns me here is the use of both replicate-do-db on the Slave and binlog-do-db on the Master at the same time.

There is no need to use both. I would remove binlog-do-db from the Master. I would also look over any queries with fully qualified table names. Why ?

If you replicate any SQL use fully qualified table names (dbname.tblname) and you use replicate-do-db, MySQL Replication gets confused if you execute USE dbname.

Percona explained this in conjunction with binlog-do-db and replicate-do-db back in May 2009.

Percona also suggested reading the replication filtering rules thoroughly.