A connection ID is a unique integer identifier that is assigned to each connection maintained within the Directory Server. It is used primarily for logging purposes, so that it is possible to correlate the various operations performed on a given connection.
The specific Implementation Configuration varies by LDAP Server Implementations implementation and you should see the specific vendor documentation for more information for your server.
Note that the connection ID counter starts at zero for the first connection received by the server and increments by one for each additional connection. The counter is reset whenever the server is restarted.
Internal connections, which are used for processing internal operations, are assigned negative values to distinguish them from connections from external clients.
There might be more information for this subject on one of the following: