title: ORA-12543: TNS:destination host unreachable
body: <p>I'm trying to study query optimization using SQL command line. When I'm about to connect to the database, I got this error. It's my first time to use the SQL command line. Ive installed Oracle database 11g express edition. The database I'm trying to access is also installed on my computer. I have a proxy network settings in my computer, which I already removed and the same error occurred. I'm using a desktop PC with W7 - 64bit OS. I'm using a wireless USB adapter to connect to the internet. I tried tnsping on my machine and returned the following lines:</p>
  
  <p><code>Used HOSTNAME adapter to resolve the alias
  Attempting to contact (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=))(ADDRESS=(PROTO
  COL=TCP)(HOST=192.168.0.20)(PORT=1521)))
  OK (70 msec)</code></p>