I have one email server, and 1 LDAP server for authentication. In my case all users should go to LDAP for authentication. For decreasing load on one LDAP server I want to share load on 2 LDAP servers instead of 1. For this I am planning to put one Load Balancer for 2 LDAP servers.

A DNS based load balancer should be enough for you. Use DNS round-robin scheme. In this scheme, set up something similar to the following (make suitable changes in IP and FQDN) in your DNS' zone file:

ldap.my.tld. IN A 10.1.1.1 ldap.my.tld. IN A 10.1.1.2

Once it is done, use ldap.my.tld wherever you need to give the host name/IP of ldap server. Your DNS will ensure that the IPs are rotated properly while serving the query for ldap.my.tld.

You can read more on DNS based load balancing in following links.

http://content.websitegear.com/article/load_balance_dns.htm http://ntrg.cs.tcd.ie/undergrad/4ba2.01/group8/DNS.html

In a load balanced scenario, it would be better to set up a master LDAP server (say, on 10.1.1.1) and another one (on 10.1.1.2) in slave mode. You need to send all updates to master server and the slave will have everything replicated automatically. See the following link for openldap.

http://www.bind9.net/manual/openldap/2.0/replication.html

Raghu