Pdf an increase in the size and requirements of a mobile workforce is. In this document lac l2tp access concentrator and client are used interchangeably, similarly lns l2tp network server and server are. Without layer 2 protocol tunneling, tunnel ports drop stp and vtp packets and process cdp packets. Layer 2 vpn architectures is a comprehensive guide to consolidating network infrastructures and extending vpn services. Layer 2 tunneling protocols, such as l2tp, do not provide encryption mechanisms for the traffic it tunnels. A vulnerability in the layer 2 tunneling protocol l2tp parsing function of cisco ios and cisco ios xe software could allow an unauthenticated, remote attacker to cause an affected device to reload. 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 pointtopoint communication. Prerequisites for layer 2 tunneling protocol version 3 beforeyouconfigureanxconnectattachmentcircuitforaprovideredge pedevice seetheconfiguring thexconnectattachmentcircuittask, theciscoexpressforwarding formerlyknownasceffeature. It does not provide any encryption or confidentiality by itself. Rfc frame relay over l2tpv3 july present in the icrq in order to identify the pvc together with the identity of the lcce itself, as defined in. Layer 2 tunneling protocol l2tp is a computer networking protocol used by internet service providers isps to enable virtual private network vpn operations.
This can be pretty usefulfor example, lets say you have two remote sites and an application that requires that hosts are on the same. An attacker could exploit this vulnerability by sending a crafted l2tp packet to an affected device. Aug 18, 2011 layer 2 tunneling protocol l2tp is a computer networking protocol used by internet service providers isps to enable virtual private network vpn operations. This document specifies a set of vendorspecific options as well as nonstandard options for layer 2 tunneling protocol ipsec. In computer networking, layer 2 tunneling protocol l2tp is a tunneling protocol used to support virtual private networks vpns or as part of the delivery of. Rfc 2661 layer two tunneling protocol l2tp ietf tools.
Traditional layer 2 networks have issues because of three main reasons. With l2tpv3, its no problem to bridge two remote sites together. This can be pretty usefulfor example, lets say you have two remote sites and an application that requires that hosts are on the same subnet. Layer 2 tunneling protocol overview techlibrary juniper. It is also possible to establish a connection using the data link layer. 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 pointtopoint. Layer two tunneling protocol l2tp specifies multi protocol access via pointtopoint protocol ppp. Layer 2 tunneling protocol version 3 thelayer2tunnelingprotocolversion3featureexpandsciscossupportoflayer2vpns. After the process is complete, the l2tp packets between the endpoints are encapsulated by ipsec.
It uses the same authentication mechanisms as pptp but its tunneling protocol is advanced as it relies on ipsec for encryption. It is a combination of the two protocols, the pptp of microsoft and the layer 2 forward l2f of cisco. Rfc 3931 layer two tunneling protocol version 3 l2tpv3. A system is provided for creating a tunneling service from the use of a traditional tunneling protocol, such as the layer two tunneling protocol l2tp. L2tpv2 layer 2 tunneling protocol l2tpv2 enables encapsulated layer 2 frames to be carried across the network. Layer 2 tunneling protocol l2tp ipsec extensions intellectual property rights notice for open specifications documentation. Click here to download a zip file of all pdf files for windows protocols. Layer 2 protocols 3 31 layer 2 protocols 3 pptp point to point tunneling protocol pptp ppp ip encapsulation for tcpip, ipx, and netbeui no encryption, but extended with rc4, pap, chap, and eap singlefactor authentication. L2tpv2 tunneling of ppp feature overview and configuration guide. Securing layer two tunneling protocol l2tp with internet protocol security ipsec is a standard that explains to users how l2tp may utilize ipsec to provide for tunnel authentication, privacy protection, integrity checking and replay protection. Find out inside pcmags comprehensive tech and computerrelated encyclopedia. L2tp, as originally defined in rfc 2661, is a standard method for tunneling pointtopoint protocol ppp sessions. L2tpv3 defines the base control protocol and encapsulation for tunneling multiple layer 2 connections between two ip nodes.
Configuring layer 2 tunneling protocol l2tp over ipsec. Layer 2 tunneling protocol l2tp ipsec extensions intellectual property rights notice for open specifications documentation technical documentation. How l2tp works the basics l2tp tunneling starts out by initiating a connection between lac l2tp access concentrator and lns l2tp network server the protocols two endpoints on the internet. In particular, the l2tp tunneling protocol, which is designed to go pointtopoint between an l2tp access concentrator lac and an l2tp network server lns, is abstracted so that l2tp becomes an access protocol to a tunneling service.
Ppp rfc1661 defines an encapsulation mechanism for transporting multiprotocol packets across layer 2 l2 pointtopoint links. Microsoft publishes open specifications documentation this documentation for protocols, file formats, data portability, computer languages, and standards support. Rather, it relies on an encryption protocol that it passes within the tunnel to provide privacy. Instead, they rely on other security protocols, such as ipsec, to encrypt their data. Like pptp, it uses a single pointtopoint connection per session. L2tp tunneling starts out by initiating a connection between lac l2tp access concentrator and lns l2tp network server the protocols two endpoints on the internet. Virtual private networks washington university in st. Ssh uses port 22 to enable data encryption of payloads being transmitted over a public network such as the internet connection. Short for layer 2 tunneling protocol, l2tp is a tunneling, session layer protocol, using the udp port 1701 on a vpn virtual private network. Introduction the layer two tunneling protocol l2tp provides a dynamic mechanism for tunneling layer 2 l2 circuits across a packetoriented data network e. It does not include any encryption and relies on other methods to provide data security and privacy, such as ipsec. Layer2controlprotocolpeering,forwarding,andtunneling 4 layer2controlprotocolpeering,forwarding,andtunneling configuringlayer2peering. In computer networking, layer 2 tunneling protocol l2tp is a tunneling protocol used to support virtual private networks vpns or as part of the delivery of services by isps. Cisco ios software layer 2 tunneling protocol l2tp denial.
Layer two forwarding l2f is a cisco tunneling protocol that uses virtual dialup networks for secure data packet transport. The layer 2 tunneling protocol l2tp is an internet engineering task force ietf standard protocol that allows ip, ipx, or netbeui traffic to be encrypted, and then sent over any medium that supports. Using such tunnels, it is possible to divorce the location of the initial dialup server from the location at which the dialup protocol connection is terminated and access to the network provided. Layer 2 tunnelling protocol version 3 is an ietf standard related to l2tp that can be used as ietf l2tpext working group rfc layer two tunneling protocol version 3 l2tpv3 rfc layer two tunneling protocol l2tp. L2tp tunnel is established between the l2tp access concentrator lac and the l2tp network server lns. In computer networking, layer 2 tunneling protocol l2tp is a tunneling protocol used to support virtual private networks vpns. Documented in rfc2661, l2tp and rfc3931, l2tpv3 are protocols for tunneling network traffic between two peers over an existing network a device running affected 12. Apr 23, 2020 layer two tunneling protocol l2tp, august canonical url. A tunnel is not encrypted by default, it relies on the tcpip protocol chosen to determine the level of security. Layer 2 tunneling protocol l2tp is an ietf standard tunneling protocol that tunnels. L2tp facilitates the tunneling of ppp packets across an intervening network in a way that is as transparent as possible to both endusers and applications.
Within the discussion of content networking, we will. Lac and an l2tp network server lns, enabling pointtopoint protocol. Layer 2 tunneling protocol l2tp is a hybrid of pptp and layer 2 forwarding l2f. Enable layer 2 protocol tunneling l2pt on a vlan on switches that do not use the the enhanced layer 2 software els configuration style which includes ex2200, ex3300, ex4200, ex4500, and ex4450 switches. Layer 2 tunneling protocol l2tp is a connectionoriented protocol that has a shared state between active endpoints. L2tpv3 layer two tunneling protocol version 3 is a pointtopoint layer two over ip tunnel. This document describes the layer two tunneling protocol l2tp which permits the tunneling of the link layer i. L2tpv2 enables pointtopoint ppp frames to be totally encapsulated within network packets, so that they can then be tunnelled through a layer 3 network.
The vulnerability is due to insufficient validation of l2tp packets. Securing layer two tunneling protocol l2tp with internet. Tunneling protocol an overview sciencedirect topics. Edge switchthe switch connected to the customer switch and placed on the boundary of the service provider network see figure 271. L2tp is one of the most widely used protocol to create a vpn connection between your device and a remote vpn server. L2f is part of the layer 2 tunneling protocol l2tp standard rfc 2661. The protocol takes various features from microsofts pptp and ciscos l2f layer 2 forwarding protocol, and improves on them. L2tp has since been adopted for tunneling a number of.
This handling of the pdus creates different spanning tree. The two endpoints of an l2tp tunnel are the initiator of the tunnel, the l2tp access concentrator lac, and the l2tp network server lns, which waits for new tunnels. Layer 2 control protocol peering, forwarding, and tunneling. The layer 2 tunneling protocol l2tp developed out of the combined work of microsoft and cisco to overcome the weaknesses of pptp and ciscos older layer 2 forwarding l2f protocol. L2tp works at layer 2, the data layer, which make it very fast, and can use x. Virtual extensible local area network vxlan is a tunneling protocol that tunnels ethernet layer 2 traffic over an ip layer 3 network.
What does layer 2 tunneling protocol actually mean. This chapter describes the routers implementation of the layer two tunnel. A user datagram protocol udp port is used for l2tp. For example, generic routing encapsulation gre can contain a layer 3 ipx packet within a layer 3 ip packet. This page and associated content may be updated frequently. Chapter 27 configuring layer 2 protocol tunneling configuring support for layer 2 protocol tunneling this example shows how to configure layer 2 protocol tunneling and drop and shu tdown thresholds on port 51 for cdp, stp, and vtp, and verify the configuration. L2tp is similar to the data link layer protocol in the osi reference model, but it is actually a session layer protocol. The layer 2 tunneling protocol l2tp allows the transmission of frames between two nodes.
Once thats achieved, a ppp link layer is enabled and encapsulated. Please refer to the current edition of the internet official protocol standards std 1 for the. Use this sample configuration to encrypt l2tp traffic using ipsec for users who dial in. For l2tpv2 these l2 frames are pointtopoint protocol ppp layer 2 frames.
Usb4tm configuration layer, usb3 tunneling, dp tunneling and. This means you can tunnel l2 protocols like ethernet, framerelay, atm, hdlc, ppp, etc. Virtual dialup allows many separate and autonomous protocol domains to share common access infrastructure including modems, access servers, and isdn routers. Lucent technologies march 2005 layer two tunneling protocol version 3 l2tpv3 status of this memo this document specifies an internet standards track protocol for the internet community, and requests discussion and suggestions for improvements. Layer 2 protocol tunneling ccie cisco certified expert. Layer 2 protocol tunneling allows layer 2 protocol data units pdus cdp, stp, and vtp to be tunneled through a network. L2tp vpn everything about layer 2 tunneling protocol. Us6094437a layer two tunneling protocol l2tp merging and. Cisco ios and ios xe software layer 2 tunneling protocol. Layer two tunneling protocol l2tp is an extension of the pointtopoint tunneling protocol pptp used by an internet service provider isp to enable the operation of a virtual private network vpn over the internet. L2f functionality is similar to the pointtopoint tunneling protocol pptp, which was developed by the microsoftled pptp forum. Layer 2 tunneling protocol ssl certificate management site.
Layer 2 tunnel protocol l2tp acts like a data link layer 2 protocol for tunneling network traffic between two peers over an existing network usually the internet. L2tp merges the best features of two other tunneling protocols. L2tp is defined in rfc 2661, layer two tunneling protocol l2tp. Apr 01, 2020 the layer 2 tunneling protocol l2tp launched in 1999 is an update on the point to point tunneling protocol pptp. Specifies the layer 2 tunneling protocol l2tp ipsec extensions, which allows ip, ipx, or netbeui traffic to be encrypted and then sent over any medium that supports pointtopoint ppp point to point protocol rfc1661 datagram delivery, such as ip, x. In contrast, a tunneling protocol encapsulates a packet of the same or lower layer. Customers layer 2 packets are encapsulated and delivered at the other end. The book opens by discussing layer 2 vpn applications utilizing both atom and l2tpv3 protocols and comparing layer 3 versus layer 2 providerprovisioned vpns. Mar 10, 2018 layer 2 protocol tunneling can be used independently or to enhance 802.