Cisco Firewall IOS question

["Chris Hughes" <chughes () rpm com>]

Cisco claims that its firewall IOS can provide secure data transfer over
public lines (such as the Internet) using any of the following protocols:

- Generic Routing Encapsulation (GRE) Tunneling

- Layer 2 Forwarding (L2F)

- Layer 2 Tunneling Protocol (L2TP)

- Quality of Service (QoS) controls: prioritize applications and allocate
network resources to ensure delivery of mission-critical application traffic

Do any of these protocols actually encrypt the data??  Seems to me that the
answer is no, but I'm not suire...

Also, Cisco claims that their network-layer encryption capability prevents
eavesdropping or tampering with data across the network during transmission.
Does anyone know what type of encryption they use?  Could this be utilized
in tandem with the aforementioned protocols to achieve security for VPN over
the internet?

Comments welcome....