[phoenix]

Originally Posted by bkarthick4u

after when i log in to administration console as sbabu@fedora.example.com,its shows that authentication failed.

Then you've given it the wrong details. Surely what you want to do is authenticate your Zimbra users for the domain which, in your example, should be example.com and you'd want this: dc=example,dc=com defined in the External Authentication set-up. What happens if you do an ldapsearch against your FDS for that user? You should also check this wiki article: LDAP Authentication - Zimbra :: Wiki