select sys_context('USERENV','HOST') from dual is null

 Hi All,

When I run: select sys_context('USERENV','HOST') from dual; from my computer(including Toad and sqlplus), I got Null value. But When I use putty connect to database server and run this SQL, I got the host name. My co-worker, his computer is in the same network with me, and when he ran this SQL from his computer, he can get host name. Anybody know how to figure out this?

Thanks a lot,

kelivn