Cisco has three main types of licenses: restricted, unrestricted, and failover. Based on the original purchase agreement, restricted licenses support only certain features and allow a fixed number of users. As you need more functionality, you can just bolt them on by ordering activation keys. An unrestricted license is exactly what it sounds like: You get all the features your PIX can provide. However, as expected, these licenses can be expensive. Lastly, failover licenses enable operation as an active or standby PIX firewall and are necessary only in failover scenarios. Additional licenses outside of the main three are available to address more advanced encryption features. For example, various licenses are available if you want to enable DES, triple DES (3DES), or AES encryption.