Lightweight Directory Access Protocol, or LDAP , is a directory services running over TCP/IP. Most large business and organization use LDAP for centralized authentication.
You can read LDAP Linux HOWTO for setup and configuration. If your workstation or server setup to authenticate via LDAP, open ssh will not work when user try to connect from remote system. You need to make little modification to openssh, so that it can authenticate you via LDAP:
Open /etc/ssh/sshd_config file
# vi /etc/ssh/sshd_config file
Append or modify line as follows:
# /etc/init.d/sshd restart
Now ssh server will accept login for remote users.