Avaya L2TP User Manual
Configuring L2TP Services
BayRS Version 12.20
Site Manager Software Version 6.20
Part No. 300016-B Rev. 00
June 1998
4401 Great America Pa rkw ay 8 Federal S treet
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300016-B 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 Ser v ic es ...................................... ...... ...... .............................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 ...............................................................................................1-12
Tunnel Authentication .............................................................................................1-12
RADIUS User Authentication .......................................... ...... ...... ....... ...... ....... ...... .1 -14
300016-B Rev. 00
v
RADIUS Accounting ................. ...... ....... ...... ....... ...... ....... ...... ...... ...........................1-15
L2TP IP Interface Addresses .................................................................................1-15
Remote Router Configuration ............... ...... ....... ...... ....... ...... .................................1-16
Where to Go Next .........................................................................................................1-17
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
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
Keeping the Remote User’s Domain Name ....................................................................3-6
Changing the Domain Name Delimiter ...........................................................................3-7
Enabling Tunnel Authentication .......................................................................................3-8
Modifying L2TP IP Interface Addresses .........................................................................3-9
Disabling RIP ..................... ...... ....... ...... ....... ...... ....... ...................................... ....... ...... .3 -10
Disabling L2TP .................................................. ....... ...... ....... ...................................... .3-1 0
Deleting L2TP from a PPP Interface .............................................................................3-11
Deleting L2TP from a Frame Relay Interface ................................................................3-12
Deleting L2TP from an ATM Interface ...........................................................................3-13
Appendix A
L2TP Parameters
L2TP Configuration Parameters .................................................................................... A-2
L2TP Tunnel Security Parameters ................................................................................. A-8
L2TP IP Interface Parameters ..................................................................................... A-10
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300016-B 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
Configuring the Dial-on-Demand Circuit ................................................................. B-6
Configuring the PPP Interface ................................................................................. B-6
Appendix C
Troubleshooting
Index
300016-B 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 1-5. Remote Router Dialing the LNS .............................................................1-16
Figure A-1. L2TP Configuration List Window ............................................................. A-2
Figure A-2. L2TP Tunnel Security List Window ......................................................... A-8
Figure A-3. L2TP IP Interface List Window .............................................................. A-10
Figure A-4. L2TP IP Interface Window .................................................................... A-10
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-B Rev. 00
ix
Tables
Table C-1. Common L2TP Network Problems and Solutions ..................................C-1
300016-B 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 You 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-Starti ng Router s , Conf igur ing BaySt ac k Remote Acc ess , or Connecting
ASN Routers to a Network).
Make sure that you are running the latest version of Bay Networks
Site Manager software. For instructions, see Upgrading Routers from Version
7-11.xx to Version 12.00 and the BayRS Version 12.20 Document Change Notice.
300016-B Rev. 00
®
BayRS™ and
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
wfsm &
dinfo
command.
Example: ATM DXI > Interf ace s > 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
nets
, you enter either
|
show at nets
or
, but not both.
300016-B Rev. 00
Acronyms
About This Guide
CHAP Challenge Handshake Authentication Protocol
IP Internet Protocol
ISDN Integrated Services Digital Network
ISP Interne t 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 Pro tocol
PAP Password Authenti cat ion 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-B Rev. 00
xv
Configuring L2TP Services
Bay Networks Technical Publications
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Internet. Go to support.baynetworks.com/library/tpubs. Find the Bay Networks
products for which you need documentation. The n locate the s pecific c ategory and
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Reader, you can open the manuals and release notes, search for the sections you
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office or account representative.
Bay Networks Customer Service
You can purchase a support contract from your Bay Networks distributor or
authorized reseller, or direct ly from Bay Networks Serv ices. For infor mation
about, or to purchase a Bay Networks service contract, either call your local Bay
Networks field sales office or one of the following numbers:
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
800-2LANW AN; th en enter Expr ess 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-B 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-B Rev. 00
Through Bay Networks Educa tional Services , you can attend cl asses and purcha se
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 existing physical infrastructu re 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-B Rev. 00
Topic Page
L2TP Benefits 1-2
What Is Tunneling? 1-2
Components of an L2TP Networ k 1-4
L2TP Packet Encapsulation 1-8
Making a Connection Across an L2TP Network 1-9
Security in an L2TP Networ k 1-10
Bay Networks L2TP Implementation 1-11
Where to Go Next 1-17
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 exis ting Inter net l eas ed conn ectio ns and res ource s at t he In ter net Se rvice
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,
eliminating long-distance toll calls required 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-base d protocol that provides great er interoperability with
networking equipment from other vendors.
What Is Tunneling?
Tunn eling i s a w ay of fo rw ardi ng traffic from remote users to a c orpora te n etwo rk
through an IP network. A tunnel is a virtual connection between two sites, for
example, an access concentrator at the ISP networ k and a router at the corporate
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) at the ISP network to an L2TP network server (LNS) at the
corporate site.
1-2
300016-B Rev. 00
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 equi pment 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 n ew 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.
300016-B Rev. 00
Packets are exchanged across an L2TP tunnel during an L2TP session. An L2TP
session is create d when an e nd-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 th e WAN packet belongs to, is negot iated bet ween
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 t he connection, en sures that p ackets are not lost, and make s sure
the devices at each end of the connection are communicating properly.
To enable flow control, see Chapter 3, “Customizing L2TP Services.”
1-3
Configuring L2TP Services
Components of an L2 TP Network
The following sections describe the components of an L2TP network. For
illustrations of L2TP networks, see Figures 1-1
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 th at uses PPP f or 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. Al l tu nnel s en d at the
LNS.
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 ha ve b uilt-in L2TP capabi lities a nd uses a LA C, rather than a
RAS.
300016-B 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 LAC refers to a remote access se rver w ith L2TP
capabilities. The term RAS refers to a remote access server without L2TP
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 inform ation about the Bay Networks implementation of the LAC in an
L2TP network, see “Bay Networks L2TP Implementation
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
” on page 1-11.
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 id ent if yin g 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-B Rev. 00
1-5
Configuring L2TP Services
L2TP Network Server (LNS)
The L2TP network server (LNS) is a router that resides at the corporate network
and serves as the termination point for L2TP tunnels and sessions.
The LNS authenticates the PPP connect ion reques t and allo ws the end- to-end PPP
tunneled connection. The LNS may also perform user authentication with a
RADIUS server to prevent unauthorized users from accessing the network;
however, user authentication may also be done by the LNS itself.
An LNS can support multip le remote users , each communi catin g withi n the ir own
L2TP session. The L2TP session is the virtual end-to-end connection over which
the LAC sends data to the LNS.
The Bay Networks router is an LNS. For information about the Bay Networks
LNS, see “Bay Networks L2T P Implementa tion
RADIUS Server
An L2TP network may include a Remote Authentication Dial-in User Service
(RADIUS) server. The RADIUS server has three main functions in an L2TP
network:
” on page 1-11.
1-6
• Authenticating the remote users
• Assigning IP addresses to the remote users
• Providing accounting services for corporate billing
The RADIUS server database centralizes the authentication function, eliminating
the need to confi gure e ach LNS with use r names a nd passw or ds. It also as signs an
IP address to a remote host to identify the host. Finally, the RADIUS server can
provide accou n ti ng s ervices for the corporate network, ca lculating billing charges
for an L2TP session.
For information about the Bay Networks implementation of RADIUS user
authentication and accounting, see “RADIUS User Authentication
and “RADIUS Accounting
” on page 1-15.
” on page 1-14
300016-B Rev. 00
Examples of L2TP Networks
Figure 1-1 shows an L2TP network that uses a LAC to connect to the LNS. The
tunnel is between the LAC and the LNS.
ISP network
L2TP Overview
Remote
host
PC
No L2TP
functionality
PPP
connection
LAC
T unnel
Data
TMS
Figure 1-1. L2TP Network Using a LAC
Figure 1-2 shows an L2TP network that uses a RAS to connect to the LNS. The
tunnel is between the PC (the L2TP client) and the LNS.
ISP network
Remote
host
PC
Tunnel
RAS
Data
Frame rela y
connection
Frame relay
connection
Corporate network
LNS
RADIUS
server
L2T0003A
Corporate network
LNS
L2TP
client
Figure 1-2. L2TP Network Using a RAS
300016-B Rev. 00
RADIUS
server
L2T0004A
1-7
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