L2TP

This section covers L2TP examples. Use it to configure LAC and LNS scenarios and related L2TP interoperability cases.

Layer Two Tunneling Protocol "L2TP" extends the PPP model by allowing the L2 and PPP endpoints to reside on different devices interconnected by a packet-switched network. L2TP includes PPP authentication and accounting for each L2TP connection. Full authentication and accounting of each connection may be done through a RADIUS client or locally. L2TP traffic uses the UDP protocol for both control and data packets. UDP port 1701 is used only for link establishment, further traffic uses any available UDP port (which can be different from 1701). This means that L2TP can be used with most firewalls and routers (even with NAT) by allowing UDP traffic through the firewall or router. The L2TP standard is defined in RFC 2661. L2TPv3 support was added in version 7.1. It supports IPv4 and IPv6.

Introduction

L2TP can be used as any other tunneling protocol with or without encryption. The L2TP standard says that the most secure way to encrypt data is with L2TP over IPsec (this is the default mode for the Microsoft L2TP client), as all L2TP control and data packets for a particular tunnel appear as homogeneous UDP/IP data packets to the IPsec system.

Multilink PPP (MP) is supported to provide MRRU (the ability to transmit full-sized 1500 and larger packets) and bridging over PPP links with Bridge Control Protocol (BCP), which allows sending raw Ethernet frames over PPP links. This allows setting up bridging without EoIP. The bridge should either have an administratively set MAC address or an Ethernet-like interface in it, as PPP links do not have MAC addresses.

Warning L2TP does not provide encryption mechanisms for tunneled traffic. IPsec can be used for additional security layers.

Quick Example

L2TP Server

On the server side, enable L2TP-server and create a PPP profile for a particular user:

[admin@MikroTik] > /interface/l2tp-server/server/set enabled=yes
[admin@MikroTik] > /ppp/secret/add local-address=10.0.0.2 name=MT-User password=StrongPass profile=default-encryption remote-address=10.0.0.1 service=l2tp

L2TP Client

This example configures an L2TP client with username "MT-User", password "StrongPass" and server 192.168.51.3:

[admin@MikroTik] > /interface/l2tp-client \
add connect-to=192.168.51.3 disabled=no name=MT-User password=StrongPass user=MT-User
[admin@MikroTik] > /interface/l2tp-client/print 
Flags: X - disabled, R - running 
0 R name="MT-User" max-mtu=1450 max-mru=1450 mrru=disabled connect-to=192.168.51.3 user="MT-User" 
password="StrongPass" profile=default-encryption keepalive-timeout=60 use-ipsec=no ipsec-secret="" 
allow-fast-path=no add-default-route=no dial-on-demand=no allow=pap,chap,mschap1,mschap2

L2TP Ether

Overview

Layer 2 Tunnel Protocol Version 3 (L2TPv3) is defined by RFC 3931 from the Internet Engineering Task Force (IETF). It introduces various improvements to the original L2TP, allowing the encapsulation of Layer 2 (L2) payloads within L2TP for use in L2 virtual private networks (VPNs).

To establish an L2TP Ether tunnel, the L2TP Ether interface must be created on the client side, while the L2TP server must be enabled on the remote (server) side. Once both sides are configured correctly, a dynamic interface is automatically created between them, forming a transparent Layer 2 connection across the IP network.

Server Side (L2TP Server)

/interface/l2tp-server/server/set enabled=yes

Client Side (L2TP Ether Interface)

/interface/l2tp-ether/add connect-to=1.1.1.1 disabled=no