RFC Layer Two Tunneling Protocol “L2TP” (Q). request for comments publication. RFC; Layer Two Tunneling Protocol. Layer Two Tunneling Protocol “L2TP”, August Canonical URL: https://www. ; File formats: Plain Text PDF; Status: PROPOSED. In computer networking, Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to Published in as proposed standard RFC , L2TP has its origins primarily in two older tunneling protocols for point-to-point communication.

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This field exists if the O bit is set. This allows the actual processing of PPP packets to be divorced from the termination of the L2 circuit. L2TP tunnels are named by identifiers that have local significance only. From Wikipedia, the free encyclopedia. Then using this tunnel and session id, data packets are exchanged with the compressed P2tp frames as payload. This field exists only if the L bit is set. To facilitate this, an L2TP session or ‘ call’ is established within the tunnel for each higher-level protocol such dfc PPP.

Indicates the identifier for a session within a tunnel.

Views Read Edit View history. The packets exchanged within an L2TP tunnel are categorized as either control packets or data packets. It may tunnel any protocol carried within PPP. RFC A device attached to the switched network fabric e. Any vendor wishing to implement their own L2TP extensions can use their own Vendor ID along with private Attribute values, guaranteeing that they will not collide with any other vendor’s extensions, nor with future IETF extensions.

Level 2 tunneling protocols have seen wide use in both small and large networks. Total length of the message in bytes.

By using this site, you agree to the Terms of Use and Privacy Policy. Retrieved from ” https: L2TP provides reliability features for the control packets, but no reliability for data packets. L2TP does not provide confidentiality or strong authentication by itself.

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RFC Layer Two Tunneling Protocol “L2TP” – Wikidata

Reliability, if desired, must be provided by the nested protocols running within each session of the L2TP tunnel. Since the L2TP packet itself is wrapped and hidden within the IPsec packet, the original source and destination IP address is encrypted within the packet.

LCP echo requests used as a keepalive for the link, for instance, should generally be sent with this bit set. Control messages MUST have this bit cleared to zero. The number of bytes contained in this AVP. Control messages MUST have this bit set.

Layer 2 Tunneling Protocol

This page was last edited on 3 Octoberat One of the aforementioned difficulties is that it is not compatible with NAT. Rfv feature is only for use with data messages. Nr, sequence number expected. RFC The variable length concatenation of a unique Attribute represented by an integer and a Value containing the actual value identified by the attribute.

Windows Vista provides two new configuration utilities that attempt to make using L2TP without IPsec easier, both described in sections that follow below:. If set, the Offset Size field is present.

Supported L2TP Standards

That is, the same session will be given different Session IDs by each end of the session. IPsec is often used to secure L2TP packets by providing confidentiality, authentication and integrity. At the time of setup of L2TP connection, many control packets are exchanged between server and client to establish tunnel and session for each direction.

To be useful for networking, higher-level protocols are then run through the L2TP tunnel. This can be represented by four different tunneling models, namely:. Indicates the sequence number expected in the next control message to be received. Multiple AVPs make up Control Messages which are used in the establishment, maintenance, and teardown of tunnels.

The value 1 is reserved to permit detection of L2F packets should they arrive intermixed with L2TP packets.


The traffic for each session is isolated by L2TP, so it is possible to set up multiple virtual networks across a single tunnel. In such a configuration, the L2 termination point and PPP session endpoint reside on the same physical device i.

Internet protocols Internet Standards Tunneling protocols Virtual private networks. Actual data within the offset padding is undefined.

If the offset field is present, the L2TP header ends after the last byte of the offset padding. Specifies the number of bytes past the L2TP header at which the payload data is expected to start.

Once a tunnel is established, the network traffic between the peers is bidirectional. L2TP allows the creation of a virtual private dialup network VPDN [5] to connect a remote client to its corporate network by using a shared infrastructure, which could be the Internet or a service provider’s network. This capability can be used to avoid the passing of sensitive data, such as user passwords, as cleartext in an AVP.

The LNS waits for new tunnels. L2TP sessions are named by identifiers that have local significance only. ATM access network extensions.

Supported L2TP Standards – TechLibrary – Juniper Networks

PPP defines an encapsulation mechanism for transporting multiprotocol packets across layer 2 L2 point-to-point links. With L2TP, a user has an L2 connection to an access concentrator e.

A secure channel refers to a connection within which the confidentiality of all data is guaranteed. That is, the same tunnel will be given different Tunnel IDs by each end of the tunnel. If the M bit is set on an unrecognized AVP within a message associated with the overall tunnel, the entire tunnel and all sessions within MUST be terminated.