The LdapPort contains the TCP port number, as a base-10 integer, that the directory service on that domain controller is using.

 <xs:element name="LdapPort" type="xs:int" />

The LdapPort element is populated from the nTDSDSA!msDS-PortLDAP attribute of the nTDSDSA object specified by the GetADDomainControllerRequest/NtdsSettingsDN (section input parameter element. If the nTDSDSA!msDs-PortLDAP attribute is not present or cannot be read due to the client lacking access rights to read the attribute, the server populates the ActiveDirectoryDirectoryServer/LdapPort element with a value of "389".