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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One of the aforementioned difficulties is that it is not compatible with NAT. This capability can be used to avoid the passing of sensitive data, such as user passwords, as cleartext in an AVP.

ZLB messages are used for explicitly acknowledging packets on the reliable control channel. The value 1 is reserved to permit detection of L2F packets should they arrive intermixed with L2TP packets. L2TP tunnels are named by identifiers that have local significance only. Indicates the L2tpp protocol version. Rather, it relies on an encryption protocol that it passes within the tunnel to provide privacy. Both these configuration utilities are not without their difficulties, and unfortunately, there is very little documentation about both “netsh advfirewall” and the IPsec client in WFwAS.

L2TP, Level 2 Tunneling Protocol

Control messages MUST have this 2661 set. The control message must then continue to be processed as if the AVP had not been present. If set, the Ns and Nr fields are present.


A secure channel refers to a connection within which the confidentiality of all data is guaranteed. If the length is set to 6, then the AVP Value field is absent.

From the end user, packets travel over a wholesale network service provider’s network to a server called a Broadband Remote Access Server BRASa protocol converter and router combined. In such a configuration, the L2 termination point and PPP session endpoint reside on the same physical device i. L2TP does not provide confidentiality or strong authentication by itself.

Retrieved from ” https: This feature is only for use with data messages. To be useful for networking, higher-level protocols are then run through the L2TP tunnel. The traffic for each session is isolated by L2TP, so it is possible to set up multiple virtual networks across a single tunnel. Since the L2TP packet itself is wrapped and rrc within the IPsec packet, the original source and destination IP address is frc within the packet. L2TP provides reliability features for the control packets, but no reliability for data packets.

This page was last edited on 3 Octoberat IPsec is often used to secure L2TP packets by providing confidentiality, authentication and integrity. Once a tunnel is established, the network traffic between the peers is bidirectional. 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.


Without it, ltp temporary interval of local congestion could result in interference with keepalive messages and unnecessary loss of the link.

Supported L2TP Standards

L2TP sessions are named by identifiers that have local significance only. This allows the actual processing of PPP packets to be divorced from the termination of rfv L2 circuit. Multiple AVPs make up Control Messages which are used in the establishment, maintenance, and teardown of tunnels.

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

The LNS waits for new tunnels.

Layer 2 Tunneling Protocol

RFC A device attached to the switched network fabric e. LCP echo requests used as a keepalive for the link, for instance, should generally be sent with this bit set.

This field exists only if the L bit is set. The number of bytes contained in this AVP.