CHAP is an authentication mechanism for point-to-point protocol connections that encrypt the user’s password. It is a protocol that uses a three-way handshake. The server sends the client a challenge, which includes a random value (a nonce) to thwart replay attacks. The client responds with a MD5 hash of the nonce and the password. The authentication is successful if the client’s response is the one that the server expected.
The VPN communication protocol standards listed above are PPTP, L2TP and IPSec.
PPTP and L2TP operate at the data link layer (layer 2) of the OSI model and enable only a single point-to-point connection per session.
The following are incorrect answers:
PPTP uses native PPP authentication and encryption services. Point-to-Point Tunneling Protocol (PPTP) is a VPN protocol that runs over other protocols. PPTP relies on generic routing encapsulation (GRE) to build the tunnel between the endpoints. After the user authenticates, typically with Microsoft Challenge Handshake Authentication Protocol version 2 (MSCHAPv2), a Point-to-Point Protocol (PPP) session creates a tunnel using GRE.
L2TP is a combination of PPTP and the earlier Layer 2 Forwarding protocol (L2F). Layer 2 Tunneling Protocol (L2TP) is a hybrid of Cisco’s Layer 2 Forwarding (L2F) and Microsoft’s PPTP. It allows callers over a serial line using PPP to connect over the Internet to a remote network. A dial-up user connects to his ISP’s L2TP access concentrator (LAC) with a PPP connection. The LAC encapsulates the PPP packets into L2TP and forwards it to the remote network’s layer 2 network server (LNS). At this point, the LNS authenticates the dial-up user. If authentication is successful, the dial-up user will have access to the remote network.
IPSec operates at the network layer (layer 3) and enables multiple simultaneous tunnels. IP Security (IPSec) is a suite of protocols for communicating securely with IP by providing mechanisms for authenticating and encryption. Implementation of IPSec is mandatory in IPv6, and many organizations are using it over IPv4. Further, IPSec can be implemented in two modes, one that is appropriate for end-to-end protection and one that safeguards traffic between networks.
Reference used for this question: Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 7067-7071). Auerbach Publications. Kindle Edition. and Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 6987-6990). Auerbach Publications. Kindle Edition.