Although really they are not necessary, they are several packages that have to be installed before openLDAP because we need them.
First of them is openSSL, also it exists in all the distributions and it has documentation in its webpage[13].
The sources can be downloaded from http://www.openssl.org/source/
The second is Kerberos Services v5, which have two implementations, one is MIT Kerberos V and the other is Heimdal Kerberos, both have good documentation and are widely supported by all the distributions.
It could also be interesting to have the Cyrus SASL libraries installed (Simple Cyrus's Authentication and Security Layer) that could be obtained from http://asg.web.cmu.edu/sasl/, Cyrus SASL makes use of openSSL and Kerberos/GSSAPI for authentication.
At last we will need a database for openLDAP, with respect to this manual this will be given through the Sleepycat Software Berkeley DB libraries, we will need it if we want to use LDBM (Berkeley DB version 3) or BDB (Berkeley DB version 4). Also they exist in the majority of the distributions.
Once obtained and compiled the necessary libraries we download the sources of openLDAP in /usr/src (for example) and decompressed in that directory (for example with tar -zxvf openldap-2.X.XX.tgz).
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