Applying IPSec to a VPN may be more complicated than it first seems, due to IPSec's interactions with other system components. Administration of a VPN's policy and configuration functions may require the use of Lightweight Directory Access Protocol (LDAP) to access a directory server. Application-level encryption such as that offered by Secure Sockets Layer (SSL) may prove complementary to that offered by IPSec, as we will discuss soon. However, some other components may prove problematic.