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.

Author: Yozshutilar Todal
Country: Armenia
Language: English (Spanish)
Genre: Spiritual
Published (Last): 15 May 2013
Pages: 227
PDF File Size: 20.38 Mb
ePub File Size: 10.41 Mb
ISBN: 198-8-64549-670-7
Downloads: 91445
Price: Free* [*Free Regsitration Required]
Uploader: Mezigore

Layer 2 Tunneling Protocol – Wikipedia

If the offset field is present, the L2TP header ends after the last byte of the offset padding. Once a tunnel is established, the network traffic between the peers is bidirectional.

The control message must then continue to be processed as if the AVP had not been present. Multiple AVPs make up Control Messages which are used in the establishment, maintenance, and teardown of tunnels. One of the aforementioned difficulties is that it is not compatible with NAT. ZLB messages are used for explicitly acknowledging packets on the reliable control channel. By using this site, you agree to the Terms of Use and Privacy Policy.

Because of the lack of confidentiality inherent in the L2TP protocol, it is often implemented along with IPsec. Reliability, if desired, must be provided by the nested protocols running within each session of the L2TP tunnel. Rather, it relies on an encryption protocol that it passes within the tunnel to provide privacy. This feature is only for use with data messages.

From the end user, packets travel over a wholesale network service provider’s network to a server called a Broadband Remote 2661 Server BRASa protocol converter and router combined. To be useful for networking, higher-level protocols are then run through the L2TP tunnel. To facilitate this, an L2TP session or ‘ call’ is established within the tunnel for each higher-level protocol such as PPP.

RFC The variable length concatenation of a unique Attribute represented by an integer and a Value containing the actual value identified by the attribute. That is, the same session will be given different Session IDs by each end of the session. Specifies the number ltp bytes past the L2TP header at which the 2661 data is expected to start. The value 1 is reserved to permit detection of L2F packets should they arrive intermixed with L2TP packets. Tunnel ID in each message is that of the intended recipient, not the sender.


Level 2 tunneling protocols have seen wide use in both small and large networks. Retrieved from rgc https: One peer requests the other peer to assign a specific tunnel and session id through these control packets. Session ID in each message is that of the intended recipient, not the sender.

Indicates the sequence number expected in the next control message to be received. This page was last edited on 3 Octoberat This can be represented by four different tunneling models, namely:. The number of bytes 266 in this AVP.

Layer 2 Tunneling Protocol

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

L2TP tunnels are named by identifiers that have local significance only. PPP defines an encapsulation mechanism for transporting multiprotocol packets across layer 2 L2 point-to-point links. L2TP allows the creation of l2tl 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.

The term tunnel-mode refers to a channel which allows untouched packets gfc one network l2fp be transported over another network. ATM access network extensions.

Supported L2TP Standards

This capability can be used to avoid the passing of sensitive data, such k2tp user passwords, as cleartext in an AVP. The packets exchanged within an L2TP tunnel are categorized as either control packets or data packets. L2TP provides reliability features for the control packets, but no reliability for data packets. That is, the same tunnel will be given different Tunnel 26661 by each end of the tunnel.


Actual data within the offset padding is undefined. Without it, a temporary interval of local congestion could result in interference with keepalive messages and unnecessary loss of the link. Published in as proposed standard RFCL2TP has its origins primarily in two older tunneling protocols for point-to-point communication: In such a configuration, the L2 termination point and PPP session endpoint reside on the same physical device i.

Windows Vista provides two new configuration utilities that attempt to make using L2TP without IPsec easier, both described in sections that follow below:.

From Wikipedia, the l22tp encyclopedia. If set, this data message should receive preferential treatment in its local queuing and transmission. Indicates the L2TP protocol version. Layer 2 Forwarding Protocol DirectAccess. This allows the actual processing of PPP packets to be divorced from the termination of the L2 circuit.

This field exists if the O bit is set. Total length of the message in bytes. It does not provide any encryption or confidentiality by itself. Also, it is not necessary to open UDP port on firewalls between the endpoints, since the inner packets are not acted upon until after IPsec data has been decrypted and stripped, which only takes place at the endpoints.

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. If the M bit is set on an unrecognized AVP within a message associated rfx a particular session, the session associated with this message MUST be terminated.