PPTP, PPPoE, and L2TP all provide OSI Layer 2 services. That is, the user of these protocols (usually, a network layer protocol suite) thinks it's running over a "normal" link layer. However, each of these protocols provides the link layer service by transporting packets over another service, rather than over the physical layer. Show
So, each of these protocols plays two different roles. Each provides a service that's a link-layer service, so looking at it from above, it's a "link layer service provider". But each runs atop a different service, so, looking from below, it's a transport service user, network service user, or link service user. Phrases like "X service user" and "X service provider" are generally more useful than the less distinct phrase "in the X layer". This user/provider distinction is an important part of the OSI layer model, though it may not be obvious from some tutorials. What Does Layer 2 Tunneling Protocol (L2TP) Mean?Layer 2 Tunneling Protocol (L2TP) is a computer networking protocol used by Internet service providers (ISPs) to enable virtual private network (VPN) operations. L2TP is similar to the Data Link Layer Protocol in the OSI reference model, but it is actually a session layer protocol. A User Datagram Protocol (UDP) port is used for L2TP communication. Because it does not provide any security for data such as encryption and confidentiality, an encryption protocol such as Internet Protocol security (IPsec) is often used with L2TP. This term is also known as Virtual Dialup Protocol. Techopedia Explains Layer 2 Tunneling Protocol (L2TP)Officially published in 1999, L2TP is an extension of Point-to-Point Tunneling Protocol (PPTP). It is the merger of two protocols, one from Microsoft (PPTP) and one from Cisco. L2TP saves the dial-up cost and overhead for any user willing to remotely connect with a site office. L2TP is known as Virtual Dialup Protocol because of its service of the Point-to-Point Protocol (PPP) extension over Internet. For example, suppose that a user in New York is connected with a traditional dial-up modem and is looking to communicate with someone in Sydney. For this purpose, the user gets a connection and establishes a dedicated link from New York to Sydney. This dedicated dial-up link will use a public switched telephone network (PSTN) and provide the lowest data transfer speed because of shared PSTN media. Thousands of other users are using the same medium, so the user will have an overall speed of 33 Kbps or worse. Instead, the user could use L2TP where PPP is used and configured at both ends (the ISP and the user site). Following the successful authentication of a user request, a tunnel is created for user data. When the tunnel is created, the user is open to start communication. Advantages of L2TP include:
The Point-to-Point Tunneling Protocol (PPTP) is an obsolete method for implementing virtual private networks. PPTP has many well known security issues. PPTP uses a TCP control channel and a Generic Routing Encapsulation tunnel to encapsulate PPP packets. Many modern VPNs use various forms of UDP for this same functionality. The PPTP specification does not describe encryption or authentication features and relies on the Point-to-Point Protocol being tunneled to implement any and all security functionalities. The PPTP implementation that ships with the Microsoft Windows product families implements various levels of authentication and encryption natively as standard features of the Windows PPTP stack. The intended use of this protocol is to provide security levels and remote access levels comparable with typical VPN products. History[edit]A specification for PPTP was published in July 1999 as RFC 2637[1] and was developed by a vendor consortium formed by Microsoft, Ascend Communications (today part of Nokia), 3Com, and others. PPTP has not been proposed nor ratified as a standard by the Internet Engineering Task Force. Description[edit]A PPTP tunnel is instantiated by communication to the peer on TCP port 1723. This TCP connection is then used to initiate and manage a GRE tunnel to the same peer. The PPTP GRE packet format is non standard, including a new acknowledgement number field replacing the typical routing field in the GRE header. However, as in a normal GRE connection, those modified GRE packets are directly encapsulated into IP packets, and seen as IP protocol number 47. The GRE tunnel is used to carry encapsulated PPP packets, allowing the tunnelling of any protocols that can be carried within PPP, including IP, NetBEUI and IPX. In the Microsoft implementation, the tunneled PPP traffic can be authenticated with PAP, CHAP, MS-CHAP v1/v2 . Security[edit]PPTP has been the subject of many security analyses and serious security vulnerabilities have been found in the protocol. The known vulnerabilities relate to the underlying PPP authentication protocols used, the design of the MPPE protocol as well as the integration between MPPE and PPP authentication for session key establishment.[2][3][4][5] A summary of these vulnerabilities is below:
EAP-TLS is seen as the superior authentication choice for PPTP;[11] however, it requires implementation of a public-key infrastructure for both client and server certificates. As such, it may not be a viable authentication option for some remote access installations. Most networks that use PPTP have to apply additional security measures or be deemed completely inappropriate for the modern internet environment. At the same time, doing so means negating the aforementioned benefits of the protocol to some point.[12] See also[edit]
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Which transport layer protocol does L2TP use?When L2TP is layered on top of IP, it uses UDP port 1701. However, in most implementations, L2TP is actually transmitted over IP via IPsec, using ESP encapsulation of UDP; this will have the packet filtering characteristics shown earlier for ESP.
What transport layer protocol does PPTP use?Which Transport layer protocol does PPTP use? - PPTP (point-to-point tunneling protocol), is an older, Layer 2 protocol developed by Microsoft that encapsulates VPN data frames. It uses TCP segments at the Transport layer.
Is L2TP a Layer 2?Layer 2 Tunneling Protocol (or L2TP) is a tunneling protocol used by both VPNs and internet service providers (ISPs). It doesn't encrypt your content but simply creates a connection between you and a VPN server.
Which port is used to establish the Layer 2 Tunneling Protocol L2TP )?Layer Two Tunneling Protocol (L2TP) uses UDP port 1701 and is an extension of the Point-to-Point Tunneling Protocol. L2TP is often used with IPSec to establish a Virtual Private Network (VPN).
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