Thanks for reply.
This is what I found perplexed me:
$ tnsping hubdb

TNS Ping Utility for Solaris: Version 8.1.5.0.0 - Production on 30-JUL-01 18:19:47

(c) Copyright 1997 Oracle Corporation. All rights reserved.

Attempting to contact (ADDRESS=(PROTOCOL=TCP)(HOST=hubdb)(PORT=1521))
TNS-12541: TNS:no listener

in the listener.ora file on hubdb the host name is written in IP address format, but tnsping returns HOSTNAME format. Because when I do tnsping and compare with other listener.ora files, whenever HOSTNAME(IP address) in listener.ora file, tnsping will return HOSTNAME(IP address), but never in a mixed format. Other than that, I can not understand why it did not work.