Avaya LT2P User Manual
Configuring
L2TP Services
BayRS V ersion 12.10
Site Manager Software Version 6.10
Part No. 300016-A Rev. 00
February 1998
4401 Great America Parkway 8 Federal Street
Santa Clara, CA 95054 Billerica, MA 01821
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300016-A Rev. 00
Contents
About This Guide
Before You Begin .............................................................................................................xiii
Conventions .....................................................................................................................xiv
Acronyms ......................................................................................................................... xv
Bay Networks Technical Publications ..............................................................................xvi
Bay Networks Customer Service .....................................................................................xvi
How to Get Help .............................................................................................................xvii
Bay Networks Educational Services ...............................................................................xvii
Chapter 1
L2TP Overview
L2TP Benefits .................................................................................................................1-2
What Is Tunneling? .........................................................................................................1-2
L2TP Sessions .........................................................................................................1-3
Components of an L2TP Network ..................................................................................1-4
Remote Host ............................................................................................................1-4
L2TP Access Concentrator (LAC) ............................................................................1-5
Remote Access Server (RAS) .................................................................................1-5
Tunnel Management Server (TMS) ..........................................................................1-5
L2TP Network Server (LNS) ....................................................................................1-6
RADIUS Server ........................................................................................................1-6
Examples of L2TP Networks ....................................................................................1-7
L2TP Packet Encapsulation ............................................................................................1-8
Making a Connection Across an L2TP Network .............................................................1-9
Security in an L2TP Network ........................................................................................1-10
Bay Networks L2TP Implementation ............................................................................1-11
Tunnel Management ...............................................................................................1-11
Tunnel Authentication .............................................................................................1-12
RADIUS User Authentication .................................................................................1-14
300016-A Rev. 00
v
RADIUS Accounting ...............................................................................................1-14
Assigned User Network Addresses .......................................................................1-15
Where to Go Next .........................................................................................................1-15
Chapter 2
Starting L2TP
Planning Considerations for an L2TP Network ...............................................................2-2
Tunnel Authentication Passwords .............................................................................2-2
RADIUS Server Information .....................................................................................2-2
Preparing a Configuration File ........................................................................................2-3
Enabling L2TP on an Unconfigured WAN Interface ........................................................2-4
Enabling L2TP on an Existing PPP Interface .................................................................2-5
Enabling L2TP on an Existing Frame Relay Interface ....................................................2-7
Enabling L2TP on an Existing ATM Interface .................................................................2-9
Chapter 3
Customizing L2TP Services
Using the MIB Object ID .................................................................................................3-2
Modifying the L2TP Protocol Configuration ....................................................................3-2
Modifying RADIUS Server Information ...........................................................................3-3
Changing the LNS System Name ...................................................................................3-4
Modifying the Number of L2TP Sessions Permitted .......................................................3-5
Enabling Tunnel Authentication .......................................................................................3-6
Modifying the Assigned User Network List .....................................................................3-7
Disabling L2TP ...............................................................................................................3-8
Deleting L2TP from a PPP Interface ..............................................................................3-9
Deleting L2TP from a Frame Relay Interface .................................................................3-9
Deleting L2TP from an ATM Interface ...........................................................................3-10
Appendix A
L2TP Parameters
L2TP Configuration Parameters .................................................................................... A-2
L2TP Tunnel Security Parameters .................................................................................A-7
Assigned User Network Parameters ..............................................................................A-9
vi
300016-A Rev. 00
Appendix B
Configuration Examples
Example 1: Remote PC Calling the Corporate Network ................................................ B-1
Configuring the Remote Hosts ................................................................................ B-2
Configuring the LACs and the TMS .........................................................................B-3
Configuring the LNS ................................................................................................ B-3
Data Path Through the Network .............................................................................. B-4
Example 2: Remote Router Calling the Corporate Network .......................................... B-5
Dial-on-Demand Circuit Configuration .................................................................... B-6
PPP Interface Configuration .................................................................................... B-6
Adjacent Host Configuration ................................................................................... B-6
Appendix C
Troubleshooting
Index
300016-A Rev. 00
vii
Figures
Figure 1-1. L2TP Network Using a LAC .....................................................................1-7
Figure 1-2. L2TP Network Using a RAS ....................................................................1-7
Figure 1-3. Packet Encapsulation Process .................................................................1-8
Figure 1-4. Tunnel Authentication Control Messages ...............................................1-13
Figure A-1. L2TP Configuration List Window ............................................................. A-2
Figure A-2. L2TP Tunnel Security List Window .......................................................... A-7
Figure A-3. Assigned User Network List Window ...................................................... A-9
Figure A-4. Assigned User Network Window ............................................................. A-9
Figure B-1. L2TP Network with PCs at the Remote Site ...........................................B-2
Figure B-2. L2TP Network with Routers at the Remote Site ..................................... B-5
300016-A Rev. 00
ix
Tables
Table B-1. IP Address Parameter ............................................................................. B-3
Table B-2. RADIUS Server Parameters ...................................................................B-3
Table B-3. Tunnel Authentication Parameters .......................................................... B-4
Table B-4. Assigned User Network Parameters ....................................................... B-4
Table B-5. PPP Demand Circuit Parameters ........................................................... B-6
Table B-6. PPP Line List Parameter ......................................................................... B-6
Table C-1. Common L2TP Network Problems and Solutions ................................... C-1
300016-A Rev. 00
xi
About This Guide
If you are responsible for configuring L2TP, you need to read this guide.
If you want to Go to
Learn about L2TP and the Bay Networks implementation of L2TP. Chapter 1
Start L2TP on a router using default parameter settings. Chapter 2
Change default settings for L2TP parameters. Chapter 3
Obtain information about Site Manager parameters (this is the same
information you obtain using Site Manager online Help).
Review configuration examples. Appendix B
Troubleshoot L2TP configuration problems. Appendix C
Appendix A
Before Y ou Begin
Before using this guide, you must complete the following procedures. For a new
router:
• Install the router (refer to the installation guide that came with your router).
• Connect the router to the network and create a configuration file (refer to
Quick-Starting Routers, Configuring BayStack Remote Access
ASN Routers to a Network)
Make sure that you are running the latest version of Bay Networks® Site Manager
and router software. For instructions, refer to the
Change Notice
300016-A Rev. 00
, or
Connecting
.
BayRS Version 12.10 Document
.
xiii
Configuring L2TP Services
Conventions
bold text
Indicates text that you need to enter, command names,
and buttons in menu paths.
Example: Enter
Example: Use the
Example: ATM DXI > Interfaces >
wfsm &
dinfo
command.
PVCs
identifies the
PVCs button in the window that appears when you
select the Interfaces option from the ATM DXI menu.
italic text
Indicates variable values in command syntax
descriptions, new terms, file and directory names, and
book titles.
quotation marks (“ ”) Indicate the title of a chapter or section within a book.
screen text
Indicates data that appears on the screen.
Example:
Set Bay Networks Trap Monitor Filters
separator ( > ) Separates menu and option names in instructions and
internal pin-to-pin wire connections.
Example: Protocols > AppleTalk identifies the
AppleTalk option in the Protocols menu.
Example: Pin 7 > 19 > 20
vertical line (|) Indicates that you enter only one of the parts of the
command. The vertical line separates choices. Do not
type the vertical line when entering the command.
Example: If the command syntax is
xiv
show at routes
show at routes
|
, you enter either
nets
or
show at nets
, but not both.
300016-A Rev. 00
Acronyms
About This Guide
CHAP Challenge Handshake Authentication Protocol
IP Internet Protocol
ISDN Integrated Services Digital Network
ISP Internet Service Provider
L2TP Layer 2 Tunneling Protocol
LAC L2TP access concentrator
LAN local area network
LCP Link Control Protocol
LNS L2TP network server
MPPP Multilink Point-to-Point Protocol
P AP Password Authentication Protocol
PPP Point-to-Point Protocol
RADIUS Remote Authentication Dial-In User Service
RAS remote access server
RIP Routing Information Protocol
SCCCN start control connection connected
SCCRP start control connection reply
SCCRQ start control connection request
TA terminal adapter
TCP/IP Transmission Control Protocol/Internet Protocol
TMS tunnel management server
UDP User Datagram Protocol
VPN virtual private network
WAN wide area network
300016-A Rev. 00
xv
Configuring L2TP Services
Bay Networks Technical Publications
You can now print technical manuals and release notes free, directly from the
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support.baynetworks.com/library/tpubs
products for which you need documentation. Then locate the specific category and
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Reader, you can open the manuals and release notes, search for the sections you
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www.adobe.com
Documentation sets and CDs are available through your local Bay Networks sales
office or account representative.
Bay Networks Customer Service
You can purchase a support contract from your Bay Networks distributor or
authorized reseller, or directly from Bay Networks Services. For information
about, or to purchase a Bay Networks service contract, either call your local Bay
Networks field sales office or one of the following numbers:
. Find the Bay Networks
.
xvi
Region Telephone number Fax number
United States and
Canada
Europe 33-4-92-96-69-66 33-4-92-96-69-96
Asia/Pacific 61-2-9927-8888 61-2-9927-8899
Latin America 561-988-7661 561-988-7550
800-2LANWAN; then enter Express
Routing Code (ERC) 290, when prompted,
to purchase or renew a service contract
978-916-8880 (direct)
978-916-3514
Information about customer service is also available on the World Wide Web at
support.baynetworks.com
.
300016-A Rev. 00
How to Get Help
If you purchased a service contract for your Bay Networks product from a
distributor or authorized reseller, contact the technical support staff for that
distributor or reseller for assistance.
If you purchased a Bay Networks service program, call one of the following Bay
Networks Technical Solutions Centers:
Technical Solutions Center Telephone number Fax number
Billerica, MA 800-2LANWAN 978-916-3514
Santa Clara, CA 800-2LANWAN 408-495-1188
Valbonne, France 33-4-92-96-69-68 33-4-92-96-69-98
Sydney, Australia 61-2-9927-8800 61-2-9927-8811
Tokyo, Japan 81-3-5402-0180 81-3-5402-0173
Bay Networks Educational Services
About This Guide
300016-A Rev. 00
Through Bay Networks Educational Services, you can attend classes and purchase
CDs, videos, and computer-based training programs about Bay Networks
products. Training programs can take place at your site or at a Bay Networks
location. For more information about training programs, call one of the following
numbers:
Region Telephone number
United States and Canada 800-2LANWAN; then enter Express Routing Code (ERC)
282 when prompted
978-916-3460 (direct)
Europe, Middle East, and
Africa
Asia/Pacific 61-2-9927-8822
Tokyo and Japan 81-3-5402-7041
33-4-92-96-15-83
xvii
Chapter 1
L2TP Overview
The Layer 2 Tunneling Protocol (L2TP) provides remote users, such as
telecommuters, mobile professionals, and personnel in remote branch offices,
with dial-in access to a corporate network. L2TP enables users to create a virtual
private network (VPN), which uses the e xisting physical infrastructure of a public
network, such as the Internet, but offers the security and exclusivity of a private
network.
This chapter contains the following information:
300016-A Rev. 00
Topic Page
L2TP Benefi
What Is Tunneling? 1-2
Components of an L2TP Network 1-4
L2TP Packet Encapsulation 1-8
Making a Connection Across an L2TP Network 1-9
Security in an L2TP Network 1-10
Bay Networks L2TP Implementation 1-11
Where to Go Next 1-15
ts 1-2
1-1
Configuring L2TP Services
L2TP Benefits
L2TP has several advantages:
• Users and businesses can take advantage of existing network equipment and
resources.
Corporations do not need to maintain and manage remote access servers and
other special networking equipment for remote users. Instead, they can use
their existing Internet leased connections and resources at the Internet Service
Provider (ISP) network, thereby significantly reducing corporate networking
and maintenance costs.
In addition, corporations do not need to provide technical support to the
remote users. Because the remote user is making a local call to the ISP, the
ISP provides technical assistance if the user has trouble making connections.
• Remote users can place a free local call to their ISP for access to the Internet.
This may not be true if they have to dial the corporate network directly.
• ISPs earn more business from corporate customers using the equipment,
thereby increasing the ISP’s revenues.
• L2TP is a standards-based protocol so it provides greater interoperability with
networking equipment from other vendors.
What Is Tunneling?
Tunneling is a way of forw arding traf fic from remote users to a corporate netw ork
through an IP network. Tunneling across an existing public network such as the
Internet creates a virtual private network that offers corporate network access to a
wider range of remote users.
L2TP is a tunneling mechanism that extends the end point of the Point-to-Point
Protocol (PPP) connection from an L2TP access concentrator (LAC) or remote
access server (RAS) to an L2TP network server (LNS).
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.
1-2
300016-A Rev. 00
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 operating properly. If the LAC
• There are no active sessions inside the 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
L2TP Overview
fails, all tunnel users are disconnected.
An individual session ends when a remote user disconnects the call, but
multiple sessions can run inside a single tunnel.
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
number
, which is a unique number for each L2TP call. This number matches the
call serial
call to the L2TP session.
300016-A Rev. 00
1-3
Configuring L2TP Services
Components of an L2TP Network
The following sections describe the components of an L2TP network. For
illustrations of L2TP networks, refer to Figures 1-
Remote Host
At the remote site is the user who wants to dial in to the corporate network. The
remote user can be located anywhere, provided that the user can dial into an ISP
network using a PC or a router. The ISP provides the connection to the Internet.
The host at the remote site can be a PC or router that uses PPP for dial-up
connections.
• If the PC or router does not have built-in L2TP software capabilities, it dials
into a LAC, which provides a tunnel across the Internet to the corporate LNS.
• If the PC or router is an L2TP client, that is, it has built-in L2TP functionality,
the L2TP client software provides a tunnel through a RAS across the Internet
to the corporate LNS. A LAC is unnecessary with an L2TP client.
The main difference between connecting an L2TP client and a nonclient is the
starting point of the tunnel. For an L2TP client, the tunnel begins at the PC or
router; for a non-L2TP client, the tunnel begins at the LAC. All tunnels end at the
LNS.
1 and 1-2 on page 1-7.
1-4
Note:
This guide’s primary focus is on an L2TP network between a remote
host that does not have built-in L2TP capabilities and uses a LA C, rather than a
RAS.
300016-A Rev. 00
L2TP Access Concentrator (LAC)
The L2TP access concentrator (LAC) resides at the ISP network. The LAC
establishes the L2TP tunnel between itself and the LNS.
Note:
In this guide, the term
capabilities. The term
capabilities.
When the remote user places a call to the ISP network, this call goes to the LAC.
The LAC then negotiates the activation of an L2TP tunnel with the LNS. This
tunnel carries data from the remote user to the corporate network.
For more information about the Bay Networks implementation of the LAC in an
L2TP network, refer to “Ba
RAS
refers to a remote access server without L2TP
y Networks L2TP Implementation” on page 1-11.
Remote Access Server (RAS)
The remote access server (RAS) resides at the ISP network. If the remote host is
an L2TP client, the tunnel is established from the remote client through a RAS to
an LNS at the corporate network. In this situation, there is no need for a LAC.
L2TP Overview
LAC
refers to a remote access server with L2TP
The RAS does not establish the tunnel; it only forwards already tunneled data to
the destination.
Tunnel Management Server (TMS)
At the ISP network, there needs to be a mechanism for identifying L2TP tunneled
users so that the LAC can construct the L2TP tunnel. Bay Networks uses a
mechanism called a tunnel management server (TMS); other vendors may use a
different method.
300016-A Rev. 00
1-5
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