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11. References

This section lists all normative and informative references cited in RFC 2661.

11.1 Normative References​

Normative references are documents required for implementing the L2TP protocol.

[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994.

  • Description: Defines the basic format and negotiation process for PPP frames tunneled by L2TP.

[RFC1662] Simpson, W., "PPP in HDLC-like Framing", STD 51, RFC 1662, July 1994.

  • Description: Defines the encapsulation method for PPP frames on HDLC-like links.

[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700, October 1994.

  • Description: IANA number assignment reference (superseded by online IANA registries).

[RFC1990] Sklower, K., Lloyd, B., McGregor, G., Carr, D., and T. Coradetti, "The PPP Multilink Protocol (MP)", RFC 1990, August 1996.

  • Description: Defines the mechanism for bundling multiple physical links into a single logical link.

[RFC1994] Simpson, W., "PPP Challenge Handshake Authentication Protocol (CHAP)", RFC 1994, August 1996.

  • Description: Authentication protocol used in L2TP proxy authentication.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

  • Description: Defines the meaning of keywords such as "MUST", "SHOULD", "MAY".

[RFC2341] Valencia, A., Littlewood, M., and T. Kolar, "Cisco Layer Two Forwarding (Protocol) 'L2F'", RFC 2341, May 1998.

  • Description: Predecessor protocol to L2TP, used for version detection.

11.2 Informative References​

Informative references provide background information and explanations of related protocols.

[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.

  • Description: Defines the IPv4 protocol on which L2TP can operate.

[RFC1334] Lloyd, B. and W. Simpson, "PPP Authentication Protocols", RFC 1334, October 1992.

  • Description: Defines PAP (Password Authentication Protocol).

[RFC2138] Rigney, C., Rubens, A., Simpson, W., and S. Willens, "Remote Authentication Dial In User Service (RADIUS)", RFC 2138, April 1997.

  • Description: Protocol for centralized authentication, authorization, and accounting.

[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998.

  • Description: Guidelines for internationalized text handling.

[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998.

  • Description: Defines IPsec architecture, recommended for use with L2TP.

[RFC2433] Zorn, G. and S. Cobb, "Microsoft PPP CHAP Extensions", RFC 2433, October 1998.

  • Description: MS-CHAPv1 protocol definition.

[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.

  • Description: Defines the IPv6 protocol on which L2TP can operate.

[RFC2759] Zorn, G., "Microsoft PPP CHAP Extensions, Version 2", RFC 2759, January 2000.

  • Description: MS-CHAPv2 protocol definition.

[KPS] Kaufman, C., Perlman, R., and M. Speciner, "Network Security: Private Communication in a Public World", Prentice Hall, March 1995, ISBN 0-13-061466-1.

  • Description: Reference book for cryptographic foundations of AVP hiding mechanism.

The following are important standards related to but not directly cited by L2TP:

L2TP Evolution:

  • RFC 3931: Layer Two Tunneling Protocol - Version 3 (L2TPv3)

    • Third version of L2TP supporting tunneling of non-PPP data frames

  • RFC 5515: Layer Two Tunneling Protocol (L2TP) Access Concentrator Configuration

    • L2TP access concentrator configuration protocol

IPsec Related:

  • RFC 2407: The Internet IP Security Domain of Interpretation for ISAKMP
  • RFC 2408: Internet Security Association and Key Management Protocol (ISAKMP)
  • RFC 2409: The Internet Key Exchange (IKE)
  • RFC 4306: Internet Key Exchange (IKEv2) Protocol
  • RFC 4555: IKEv2 Mobility and Multihoming Protocol (MOBIKE)

PPP Extensions:

  • RFC 2637: Point-to-Point Tunneling Protocol (PPTP)
  • RFC 3748: Extensible Authentication Protocol (EAP)
  • RFC 5281: Extensible Authentication Protocol Tunneled Transport Layer Security Authenticated Protocol Version 0 (EAP-TTLSv0)

QoS and Traffic Management:

  • RFC 2474: Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
  • RFC 2475: An Architecture for Differentiated Services

11.4 Standards Organizations​

IETF (Internet Engineering Task Force)

IANA (Internet Assigned Numbers Authority)

IEEE (Institute of Electrical and Electronics Engineers)

  • Standards related to Layer 2 technologies

ITU-T (International Telecommunication Union - Telecommunication Standardization Sector)

  • Q.931: ISDN signaling (referenced in Q.931 Cause Code AVP)

11.5 Historical Context​

The L2TP protocol is a merger of two protocols:

  1. L2F (Layer 2 Forwarding Protocol) - Developed by Cisco Systems

    • RFC 2341

  2. PPTP (Point-to-Point Tunneling Protocol) - Developed by Microsoft and others

    • RFC 2637

L2TP combines the advantages of both protocols and became an IETF standards track protocol.

11.6 Further Reading​

Technical Books:

  • "VPN and NAT Traversal" by Gurdeep Singh Pall and Glen Zorn
  • "Understanding Virtual Private Networks" by Rod Rhoton
  • "Virtual Private Networks: Technologies and Solutions" by Ruixi Yuan and W. Timothy Strayer

Online Resources:

Citation Format Notes:

In this document, references to RFCs use the format [RFCXXXX], where XXXX is the RFC number. References to other documents use short identifiers in square brackets (e.g., [KPS]).

Complete RFC documents can be obtained from:

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