Prevent same user from multiple host

[chani]

Hi ,

We are using open LDAP to authenticate the users of our
network.
At the moment a user can log in to more than one machine at the same
time
Using is login. I want to prevent it.

I mean while a user logged in to one host he should not be
able to
logged in to another machine same time. How can I do this.

Thank you for any idea.