wsrep_cluster_status ... disconnected

I installed MariaDB_galera_server-5.5 and I configured the galera_cluster as following :

sudo nano /etc/mysql/conf.d/cluster.cnf

 [mysqld]
query_cache_size=0
binlog_format=ROW
default-storage-engine=innodb
innodb_autoinc_lock_mode=2
query_cache_type=0
bind-address=0.0.0.0


wsrep_provider=/usr/lib/galera/libgalera_smm.so
wsrep_provider_options="gcache.size=32G"

wsrep_cluster_name="test_cluster"
wsrep_cluster_address="gcomm://192.168.xx.xx"
wsrep_sst_method=rsync
wsrep_node_address="192.168.xx.xx"
wsrep_node_name="this_node_name"

but when iI check the wsrep status in MariaDB it shows disconnected

MariaDB [(none)]> show status like 'wsrep%';
+--------------------------+----------------------+
| Variable_name            | Value                |
+--------------------------+----------------------+
| wsrep_cluster_conf_id    | 18446744073709551615 |
| wsrep_cluster_size       | 0                    |
| wsrep_cluster_state_uuid |                      |
| wsrep_cluster_status     | Disconnected         |
| wsrep_connected          | OFF                  |
| wsrep_local_index        | 18446744073709551615 |
| wsrep_provider_name      |                      |
| wsrep_provider_vendor    |                      |
| wsrep_provider_version   |                      |
| wsrep_ready              | ON                   |
+--------------------------+----------------------+