Nortel Networks manual L2TP Sessions

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L2TP Overview

Multiple users can communicate through a single tunnel between the same LAC and LNS pair. Each user transmits and receives data in an individual L2TP session.

The LAC brings down the tunnel for any one of the following reasons:

•A network failure occurs.

•The LAC or other equipment at the ISP is not op erating properly. If the LAC fails, all tunnel users are disconnected.

•There are no active sessions inside the tunnel.

An individual session ends when a remote user disconnects the call, but multiple sessions can run inside a single tunnel.

•The system administrator at the ISP terminates the user connection.

•The LAC is not responding to a Hello packet from the LNS.

For the LAC to reestablish a tunnel, the remote user has to place a new call.

L2TP Sessions

Packets are exchanged across an L2TP tunnel during an L2TP session. An L2TP session is created when an end-to-end WAN connection is established between the remote host and the LNS.

The L2TP portion of the packets sent through the tunnel contains a header with a call ID field (also called a session ID) and a tunnel ID field. The call ID field, which indicates the session that the WAN packet belongs to, is negotiated between the LAC and the LNS when the L2TP call is set up. The tunnel ID specifies the tunnel that the L2TP session is using.

In addition to the fields in the header, the L2TP packet contains a call serial number, which is a unique number for each L2TP call. This number matches the call to the L2TP session.

For an L2TP session, you can enable flow control. Flow control manages congestion across the connection, ensures that packets are not lost, and makes sure the devices at each end of the connection are communicating properly.

To enable flow control, see Chapter 3, “ Customizing L2TP Services.”

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Contents Configuring L2TP Services Copyright 1998 Bay Networks, Inc Bay Networks, Inc. Software License Agreement Rev Contents Chapter Starting L2TP Appendix B Configuration Examples Page Figures Page Tables Page Before You Begin PrefaceItalic text Text ConventionsAcronyms Bay Networks Technical Publications How to Get HelpTopic Chapter L2TP OverviewL2TP Benefits What Is Tunneling?L2TP Sessions Remote Host Components of an L2TP NetworkRemote Access Server RAS L2TP Access Concentrator LACTunnel Management Server TMS Radius Server L2TP Network Server LNSExamples of L2TP Networks L2TP Network Using a LACPacket Encapsulation Process L2TP Packet EncapsulationMaking a Connection Across an L2TP Network Security in an L2TP Network Bay Networks L2TP Implementation Tunnel Management Tunnel AuthenticationShows tunnel authentication Radius User Authentication L2TP IP Interface Addresses Radius AccountingRemote Router Dialing the LNS Remote Router ConfigurationIf you want to Go to Where to Go NextPage Chapter Starting L2TP Planning Considerations for an L2TP Network Tunnel Authentication PasswordsRadius Server Information Choose Local File , Remote File , or Preparing a Configuration FileSite Manager Procedure You do this System responds Tools Choose Configuration ManagerSubnet Mask Enabling L2TP on an Unconfigured WAN InterfaceChoose Edit Circuit Enabling L2TP on an Existing PPP InterfaceChoose Add/Delete Configuring L2TP Services Enabling L2TP on an Existing Frame Relay Interface Configuration is completed Choose Group Protocols Site Manager ProcedureEnabling L2TP on an Existing ATM Interface You do this System respondsChoose Protocols Choose Service AttributesChapter Customizing L2TP Services Choose L2TP Configuration Modifying the L2TP Protocol ConfigurationRadius Server on Modifying Radius Server InformationChanging the LNS System Name Modifying the Number of L2TP Sessions Permitted Set the Remove Domain Name Keeping the Remote User’s Domain NameSet the Domain Name Delimiter Changing the Domain Name DelimiterChoose Tunnel Authentication Enabling Tunnel AuthenticationChoose L2TP IP Interface Modifying L2TP IP Interface AddressesDisabling L2TP Disabling RIPDeleting L2TP from a PPP Interface Customizing L2TP ServicesDeleting L2TP from a Frame Relay Interface Deleting L2TP from an ATM Interface Site Manager Procedure Topic Appendix a L2TP ParametersFigure A-1. L2TP Configuration List Window L2TP Configuration ParametersParameter Max L2TP Sessions Parameter Enable L2TPParameter Receive Window Size Parameter Hello Timer seconds Parameter Retransmit Timer secondsParameter Maximum Retransmit Parameter LNS System Name Parameter Ack Timeout millisecondsParameter Radius Primary Server IP Address Parameter Radius Client IP Address Parameter Radius Primary Server PasswordParameter Tunnel Flow Control Parameter Domain Name Delimiter Parameter Remove Domain NameFigure A-2. L2TP Tunnel Security List Window L2TP Tunnel Security ParametersParameter Tunnel Authentication Password Parameter Enable Tunnel AuthenticationFigure A-3. L2TP IP Interface List Window L2TP IP Interface ParametersParameter Subnet Mask Parameter L2TP IP Interface AddressParameter RIP Enable Example 1 Remote PC Calling the Corporate Network Appendix B Configuration ExamplesFigure B-1. L2TP Network with PCs at the Remote Site Configuring the Remote HostsParameter Name Value IP Address 192.32.16.55 Configuring the LACs and the TMSConfiguring the LNS Domain name baynetworks.comL2TP IP Interface window, enter the L2TP IP address Data Path Through the NetworkFigure B-2. L2TP Network with Routers at the Remote Site Example 2 Remote Router Calling the Corporate NetworkConfiguring the PPP Interface Configuring the Dial-on-Demand CircuitParameter Name Value RFC1661 Compliance Enable Problem What to Do Appendix C TroubleshootingTable C-1 Common L2TP Network Problems and Solutions L2TP IndexIndex-2

L2TP specifications

Nortel Networks L2TP, or Layer 2 Tunneling Protocol, is a widely recognized networking protocol that enables the tunneling of data over various networks. Initially developed as an extension of the Point-to-Point Tunneling Protocol (PPTP), L2TP integrates components from both PPTP and Layer 2 Forwarding (L2F). Nortel Networks played a significant role in the development and implementation of L2TP, making it a prominent choice for service providers and enterprise networks seeking secure and efficient connectivity.

One of the primary features of L2TP is its ability to encapsulate data packets, allowing the transport of PPP (Point-to-Point Protocol) frames without necessitating the traditional point-to-point connections. This means L2TP can operate across different networks, facilitating remote access connections and VPNs (Virtual Private Networks). As a result, organizations can achieve greater flexibility in managing their communications infrastructure.

Another key characteristic of L2TP is its support for both IPv4 and IPv6, ensuring compatibility with current and future networking environments. L2TP operates at the link layer of the OSI model, which means it functions between the data link and network layers, making it versatile for various applications. By using UDP (User Datagram Protocol) as a transport protocol, L2TP ensures efficient data transmission while maintaining lower latencies.

Security is a critical aspect of L2TP. While L2TP itself does not provide encryption, it is often paired with IPSec (Internet Protocol Security) for enhanced security protocols. This combination offers both tunneling and encryption, creating a secure framework for transmitting sensitive information across potentially insecure networks, such as the Internet.

L2TP also features various authentication methods, allowing for robust access control. It supports various schemes like PAP (Password Authentication Protocol) and CHAP (Challenge Handshake Authentication Protocol), giving network administrators a range of options to ensure the legitimacy of users accessing the network.

In summary, Nortel Networks L2TP is a powerful tunneling protocol known for its flexibility, compatibility, and security features. Its ability to encapsulate data for efficient transport makes it ideal for remote access and VPN applications. As organizations continue to demand secure, seamless connectivity, L2TP remains a resilient choice within the shifting landscape of networking technologies.
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