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
Santa Clara, CA 95054 Billerica, MA 01821

Copyright © 1998 Bay Networks, Inc.

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300016-B Rev. 00

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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

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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

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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

You can now print technical manuals and release notes free, directly from the
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
model or version for your hardware or software product. Using Adobe Acrobat
Reader, you can open the manuals and release notes, search for the sections you
need, and print them on most s tandard prin ters. You can download Acrobat Reader
free from the Adobe Systems Web site, www.adobe.com.

Documentation sets and CDs are a vailable through your local Bay Networ ks sales
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

Configuring L2TP Services

L2TP Packet Encapsulation

The PC or router at the remote site sends PPP packets to the LAC. The LAC
encapsulates these incoming packets in an L2TP packet and sends it across an IP
network through a bidirectional tunnel. After the LNS receives the packets, it
decapsulates them and terminates the PPP connection.

Figure 1-3

network.

Layer 2
protocol

shows how data is encapsulated for transmission over an L2TP

Remote user places a call

LAC

LNS

DATA

PPP

IPL2TP

DATA

PPP IP

IP/UDP

1-8

IP DATA

Data packet moves to the corporate network

L2T0005A

Figure 1-3. Packet Encapsulation Process

300016-B Rev. 00

Making a Connection Across an L2TP Network

The following steps explain how a remote user connects across an L2TP network
that includes a Bay Networks LAC, TMS, and LNS (see Figure 1-1

1.

The remote user dials a LAC at the local ISP network to establish a PPP
connection to the corporate network.

In the call, the user incl udes any required information, for example, a user
name, including a domain name, and a password. When the user dials in, he
enters a name, for example, [e-mail]; jdoe is the user name
and baynetworks.com is the domain name.

2.

The LAC receives the call and passes the domain name to the TMS.
If the TMS finds a match for the domain name, a tunnel can be created. The

TMS also checks the number of current connections so that they will not
exceed the maximum number allowed.

If the user is not a tunnel candidate, as determined by the domain name, the
LAC assumes that the remote host is making a regular dial-in request and
authenticates the user accordingly.

L2TP Overview

on page 1-7).

300016-B Rev. 00

3.

The LAC tries to establish an L2TP tunnel with the LNS.
For the LAC to send a tunnel request to the LNS, it needs the address of the

LNS. The LAC requests the address from the TMS. It then checks for this
address in its own routing table. After obtaining the address, the LAC sends a
tunnel request to the LNS. The LNS may perform tunnel authentication, if
configured to do so. If the LAC and LNS complete tunnel authentication
successfully, the LAC establishes the tunnel.

4.

After the tun nel is establis hed, the LAC forwards the remote user’s name to
the LNS, which verifies the user’s identity with the corporate RADIUS server.

If the RADIUS server recognizes the user name, it replies with an
acknowledgment and an IP address that it assigns to the remote user for the
duration of the call. This IP address identifies the remote user who may not
have an address of his own.

5.

After the remote user i s succ essfu ll y auth entic ate d, the user h as an e nd- to-en d
PPP connection to the corporate network over the Internet.

The tunnel can now carry a user session during which the LAC and the LNS
exchange PPP packets.

1-9

Configuring L2TP Services

Security in an L2TP Network

You can configure two layers of security in an L2TP network:

• Tunnel authent i cat ion

Tunnel authentication is the process of negotiating the establishment of a
tunnel between the LAC and the LNS.

• User authentication

The network administrator at the corporate site can configure a RADIUS
server with th e names and passwords of authorized users. The server’s
database centralizes the authentication function, eliminating the need to
configure each LNS with user names and passwords.

When the LNS receives a call, it forwards the user information to the
RADIUS server, which verifies whet her the user is authorized to access the
network.

You can also configure the LNS to perform user authentication if a RADIUS
server is not part of the network configuration.

For more information about the Bay Networks implementation of tunnel and user
authentication, see “Tunnel Authenticati on

Authentication” on page 1-14.

” on page 1-12 and “RADIUS User

1-10

300016-B Rev. 00

Bay Networks L2TP Implementation

In an L2TP network, the Bay Netw or ks rout er is th e LNS. LNS software operates

®

on the BLN
The Bay Networks LNS has the following characteristics:

• Each slot can act as an LNS, which means that one rou ter can ha v e many LNS

interfaces, eac h with its o wn address . You can have as many LNS inte rface s as
there are available slots on the router.

• The LNS performs user authentication with a RADIUS server to prevent

unauthorized users from accessing the network.

• The LNS accepts only incoming calls; it does not place calls to the LAC.

• The Bay Networks L2TP implementation supports only IP traffic through the

L2TP tunnel. The LNS supports only numbered IP addresses.

• The router interface between the ISP and the corporate network (see

Figure 1-1

(including PPP multilink), or ATM. Bay Networks recommends that you use a
high-speed link, such as T1, for the leased connection.

, BCN®, and ASN™ platforms.

on page 1-7) is a leased line operating with frame relay, PPP

L2TP Overview

300016-B Rev. 00

• The LNS terminates PPP multilink and PPP encapsulated data within an

L2TP packet.

• The LNS operates with the LAC implementation configured on the Bay

Networks Model 5399 Remote Access Concentrator.

• The host (PC or router) dialing into the ISP network can be on the same

subnet as the IP interface on the LNS.

• The LNS supports RIP. RIP is particularly useful when the remote host is a

router, because it enables the LNS to learn routing information from the
remote router.

For instructions on how to configure a Bay Networks router as an LNS, see
Chapter 2, “Starting L2TP.”

1-11

Configuring L2TP Services

Tunnel Management

The Bay Networks tunnel management server (TMS), which resides at the ISP
network, stores the TMS database. This database contains the remote users’
domain name, the IP address information of each LNS, and other tunnel
addressing information that the network administrator configures. The LAC
requests this information from the TMS to construct the L2TP tunnel.

When the LAC receives a call, it forwards the domain name to the TMS. The
domain name is the porti on of the user’s address that specif ies a parti cular locat ion
in the network. For example, if the user name is [e-mail],
baynetworks.com is the domain name. The TMS looks up the domain name and
verifies that the remote user is an L2TP user. The TMS also provides the LAC
with the addressing information required to establish a tunnel to the correct LNS.

Note:

The domain name referred to in this guide is a domain identifier that
does not follo w a specif ic f ormat. It is not r elated to an y Domain Name Sy stem
(DNS) protocol requirements.

Tunnel Authentication

1-12

For security purposes, you can enable the LNS to perform tunnel authentication.
Tunnel authentication is the process of negotiating the establishment of a tunnel.

During tunnel authentication, the LNS identifies the L2TP c lient or LAC by
comparing the LAC’s tunnel authentication password with its own password. If
the passwords match, the LNS permits the LAC to establish a tunnel.

The LAC does not send the tunnel authentication password as a plain-text
message. The exchange of passwords works much like the PPP Challenge
Handshake Authenti cation Protoc ol (CHAP). When one si de recei v es a chal lenge,
it responds with a value that is calculated based on the authentication password.
The receiving side matches the value against its own calculation. If the values
match, authentication is successful.

Tunnel authentication occurs in both directions, which means that the LAC and
LNS both try to verify the other’s identity.

300016-B Rev. 00

L2TP Overview

You can enable tunnel authentication on the Bay Networks LNS. If tunnel
authentication is d isa bl ed, whi ch i s t he default, the LNS sends a default chall en ge
response to the LAC during the authentication process so that the tunnel can be
established. The LNS cannot send outgoing calls, so it cannot initiate tunnel
authentication.

During tunnel authentication, the following exchange of messages takes place:

1.

The LAC sends a tunnel setup message, called the start control connection
request (SCCRQ) mess a ge to the LNS. This message includes a challenge to
the LNS.

2.

The LNS replies with a tunnel response, a challenge response, and its own
challenge message. This is called the start control connection reply (SCCRP)

message.

3.

The LAC replies with a challenge response that includes its tunnel
authentication password. This is the start control connection connected

(SCCCN) message.

4.

If this same password is configured for the LNS, the LNS grants approval to
the LAC to establish a tunnel.

300016-B Rev. 00

Figure 1-4

shows tunnel authentication.

ISP network

PPP connection

LAC

SCCRQ

tunnel request and challenge

tunnel response, challenge response,

and LNS challenge

SCCCN

challenge response

Figure 1-4. Tunnel Authentication Control Messages

Corporate network

LNS

SCCRP

L2T0006A

1-13

Configuring L2TP Services

After tunnel authentication is complete, it does not need to be repeated for other
calls to the same LAC.

RADIUS User Authentication

RADIUS user authenticat ion is ena bled b y def ault on t he Bay Netw orks LNS; yo u
must configure this feature so that the LNS can validate the remote user’s identity
before allowing access to the network.

The network administrator at the corporate site must configure a RADIUS server
with the names and passwords of authorized users. When the LNS recei ves a call,
it forwards an authentication request with the user information to the RADIUS
server, which verifies whether the user is authorized. If the user is permitted
access to the network, the RADIUS server replies with an acknowledgment
message and the appropriate IP address for that user to make a connection.

The IP address that the RADIUS server assigns is essential because many remote
hosts may not have their own addresses. The LNS uses the address to identify the
remote host and send data to the remote user. After the session ends, the IP
address becomes available for another user.

1-14

If the corporate network uses an existing RADIUS database for L2TP
connections, you do not have to reconfigure the names in the database. The LNS
automaticall y remo v es the d omain p ortio n of the user n ame tha t is i ncluded as par t
of the call from the LAC to the LNS. If you want to keep the domain name, you
can disable this feature. For instructions, see Chapter 3, “Customizing L2TP
Services.”

For more inform ation about configuring Bay Networks routers as RADIUS
servers, see Configuring RADIUS.

300016-B Rev. 00

RADIUS Accounting

The RADIUS server can provide accounting services in addition to its
authentication services. RADIUS accounting is enabled by default on the Bay
Networks LNS.

The RADIUS accounting server calculates billing charges for an L2TP session
between the remote user and the LNS. To determine thes e char g es, the s erv e r uses
information that it receives from the LNS, such as the status of each call and the
number of packets sent during the session. Using this data, the server determines
billing char ges, whi ch the netw or k admin istr ator can use to man age net w ork co sts.

The primary RADIUS accounting server can be the same server as the
authentication server or it can be a different server.

For more information about RADIUS accounting, see Configuring RADIUS.

L2TP IP Interface Addresses

When configuring the Bay Networks LNS, you must configure an IP address for
every slot that has an L2TP interface. This address is referred to as the L2TP IP
interface address. The L2TP IP interface can be any valid IP address.

L2TP Overview

300016-B Rev. 00

The L2TP IP interface address is internal to the LNS. When communicating with
the remote user , the LNS associates the user’s IP address, which is assigned b y the
RADIUS server, with the L2TP IP interface address that you configured.

The L2TP IP interface address and the RADIUS-assigned IP address do not have
to be in the same subnet.

1-15

Configuring L2TP Services

PC 1

PC 2

LAC

192.168.18.41

192.32.25.34

192.32.25.35

Dial-in router

LNS

192.168.19.34

L2TP IP, RIP enabled

192.32.33.94

LAN interface
RIP enabled

192.32.25.33

Dial-on-demand
RIP enabled
Dial-optimized
routing enabled

192.32.25.66

L2T0009B

Remote Router Configuration

If the host at the remote site is a Bay Networks router, you may need to configure
a dial-on-dema nd circu it for the rem ote rout er’s dial-up interf ace to the LAC at the
ISP network.

Enable RIP on both the dial-on-demand circuit and the attached LAN interface of
the remote router, so that the LNS can learn routin g information from the remote
router . To av oid unneces sarily acti v ating the circuit bec ause of RIP pack ets, enabl e
dial-optimized routing for the dial-on-demand circuit (see Figure 1-5

In addition, conf igu re a def ault or stati c route f or the remote ro uter , which us es the
next-hop address that corresponds to the L2TP IP interface address of the LNS.
This default or static route enables the remote router to deliver L2TP packets to
the LNS.

).

1-16

Figure 1-5. Remote Router Dialing the LNS

300016-B Rev. 00

Where to Go Next

Go to one of the following chapters for more information:

If you want to Go to

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

L2TP Overview

Appendix A

300016-B Rev. 00

1-17

Chapter 2

Starting L2TP

The quickest way to start L2TP is to ena ble it with the default configuration that
Bay Networks software supplies. This configuration uses all available parameter
defaults. You need to supply values for several parameters that do not ha v e de fa ult
values.

This chapter includes the following information:

Topic Page

300016-B Rev. 00

Planning Considerations for an L2TP Net work 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

2-1

Configuring L2TP Services

Planning Considerations for an L2TP Network

This guide primarily explains how to configure a Bay Networks BLN, BCN, or
ASN router as an LNS in an L2TP network. To successfully operate in an L2TP
network, obtain the following information to configure the LNS.

Tunnel Authentication Passwords

If you plan to enable tunnel authentication, which is optional for the Bay
Networks LNS, you must obtain the LAC password from your ISP. For more
information about the authentication process, see “Tunnel Authentication” on
page 1-12.

RADIUS Server Information

The Bay Networks implementation of L2TP requires that you configure a
RADIUS server to perform user authentication and to assign IP addresses to
remote users.

For the RADIUS server, do the following:

2-2

• Configure the RADIUS server with user names and domain names.

• Obtain the address and password of the RADIUS server to enter in the LNS

configuration.

• Configure the RADIUS server to assign IP addresses to remote users.

This address identifies the remote user to the LNS during an L2TP session. If
the remote user does not have a preconfigured address, the onl y way to assign
addresses is by the RADIUS server. This address is also used for network
communication across the subscriber network.

For more inform ation about configuring Bay Networks routers as RADIUS
servers, see Configuring RADIUS.

300016-B Rev. 00

Preparing a Configura tion File

Before starting L2TP, you must create and save a configuration file with at least
one WAN interface, for example, a synchronous or MCT1 port.

For information about the Site Manager configuration tool and how to work with
configuration files, see Configuring and Managing Routers with Site Manager.

To open the configuration file, complete the following tasks:

Site Manager Procedure

You do this System responds

Starting L2TP

1. In the main Site Manager window, choose
.

Tools

2. Choose

3. Choose

Dynamic

4. Select the file and click on OK. The Configuration Manager window

Configuration Manager

Local File, Remote File

.

. The Configuration Manager window

, or

The Tools menu opens.

opens.
Site Manager prompts you for the

configuration file you want to open.

opens, displaying the router modules.

From the Configuration Manager window, go to one of the following sections to
enable L2TP:

Section Page

Enabling L2TP on an Unconfigured WAN Interface
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

2-4

300016-B Rev. 00

2-3

Configuring L2TP Services

Enabling L2TP on an Unconfigured WAN Interface

To enable L2TP on an unconfigured WAN interface, complete the followi ng tasks :

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

choose a WAN connector.

2. Accept the default circuit name or change

it, then click on OK.

3. Choose

click on OK.

4. Choose

5. Enter the IP address of the LNS (router),

then click on OK.

6. Set the following parameters:

• RADIUS Primary Server IP Address

• RADIUS Primary Server Password

•

7. Click on OK. The L2TP Tunneling Security w indow

8. Click on OK. The L2TP IP Interf ace List w indow ope ns,

9. Set the following parameters:

• L2TP IP Interface Address

•

PPP, Frame Relay

, then click on OK. The IP Configuration window opens.

L2TP

RADIUS Client IP Address

Click on
descriptions beginning on page A-5.

Subnet Mask

or see the param eter

Help

, or

ATM

then

The Add Circuit window opens.

The WAN Protocols window opens.

The Select Protocols window opens.

The L2TP Configuration window opens.

opens.

followed by the L2TP IP Configuration
window.

Site Manager displays a message
alerting you of the time delay to create
the L2TP tunnel circuits.

2-4

Click on
descriptions beginning on page A-11.

10. Click on OK. You return to the L2TP IP Interface List

or see the param eter

Help

window, which displays the IP interface
address and the subnet mask. A
message windo w opens that r eads,

Configuration is completed

L2TP

.

(continued)

300016-B Rev. 00

Starting L2TP

Site Manager Procedure

You do this System responds

11. Click on OK.

12. Click on

. You return to the Configuration Manager

Done

(continued)

window.

Enabling L2TP on an Existing PPP Interface

To enable L2TP on an interface with PPP and IP already enabled, complete the
following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

choose a WAN connector.

2. Choose

3. Choose

the window.

4. Choose

5. Choose

6. Set the following parameters:

• RADIUS Primary Server IP Address

• RADIUS Primary Server Password

•

Edit Circuit
Protocols

Add/Delete
L2TP

RADIUS Client IP Address

. The Circuit Definition window opens.

in the top left corner of

. The Select Protocols window opens.

, then click on OK. The L2TP Configuration window opens.

The Edit Connector window opens.

The Protocols menu opens.

300016-B Rev. 00

Click on
descriptions beginning on page A-5.

7. Click on OK. The L2TP Tunneling Security w indow

8. Click on OK. The L2TP IP Interf ace List w indow ope ns,

or see the parameter

Help

opens.

followed by the L2TP IP Configuration
window.

(continued)

2-5

Configuring L2TP Services

Site Manager Procedure

(continued)

You do this System responds

9. Set the following parameters:

• L2TP IP Interface Address

• Subnet Mask

Click on

or see the parameter

Help

Site Manager displays a message
alerting you of the time delay to create
the L2TP tunnel circuits.

descriptions beginning on page A-11.

10. Click on OK. You return to the L2TP IP Interface List

window, which displays the IP interface
address and the subnet mask. A
message windo w opens that r eads,

Configuration is completed

L2TP

.

11. Click on OK.

12. Click on

. You return to the Circuit Definition

Done

window.

13.Choose

14.Choose

. The File menu opens.

File

. You return to the Configuration Manager

Exit

window.

2-6

300016-B Rev. 00

Enabling L2TP on an Existing Fra m e Relay Interface

T o enable L2 TP on an interfa ce with f rame rela y and IP al ready ena bled, compl ete
the following tasks:

Site Manager Procedure

You do this System responds

Starting L2TP

1. In the Configuration Manager window,

choose a WAN connector.

2. Choose

3. Choose

4. Choose

the window.

5. Choose

6. Choose

7. Set the following parameters:

• RADIUS Primary Server IP Address

• RADIUS Primary Server Password

•

8. Click on OK. The L2TP Tunneling Security w indow

9. Click on OK. The L2TP IP Interf ace List w indow ope ns,

10. Set the following parameters:

• L2TP IP Interface Address

• Subnet Mask

Edit Circuit

Services

Protocols

Add/Delete
L2TP

RADIUS Client IP Address

Click on
descriptions beginning on page A-5.

Help

. The Frame Relay Circuit D efinition

. The Frame Relay Servic e List window

in the top left corner of

. The Select Protocols window opens.

, then click on OK. The L2TP Configuration window opens.

or see the parameter

The Edit Connector window opens.

window opens.

opens.
The Protocols menu opens.

opens.

followed by the L2TP IP Configuration
window.

Site Manager displays a message
alerting you of the time delay to create
the L2TP tunnel circuits.

300016-B Rev. 00

Click on
descriptions beginning on page A-11.

or see the param eter

Help

(continued)

2-7

Configuring L2TP Services

Site Manager Procedure

(continued)

You do this System responds

11. Click on OK. You return to the L2TP IP Interface List

window, which displays the IP interface
address and the subnet mask. A
message windo w opens that r eads,

Configuration is completed

L2TP

.

12. Click on OK.

13. Click on

. You return to the Frame Relay Service

Done

List window.

14. Click on

. You return to the Frame Relay Circuit

Done

Definition window.

15. Click on

. You return to the Configuration Manager

Done

window.

2-8

300016-B Rev. 00

Enabling L2TP on an Existing ATM Interface

To enable L2TP on an interf ace with ATM and IP already enabled, you ca n enab le
L2TP in two ways. If your interface uses a COM connector, complete the tasks in
the following table. If your interface uses an AT M connector, go to page 2-10

Site Manager Procedure

You do this System responds

Starting L2TP

.

1. In the Configuration Manager window,

choose a WAN connector.

2. Choose

3. Choose

4. Choose

5. Choose

6. Set the following parameters:

• RADIUS Primary Server IP Address

• RADIUS Primary Server Password

•

7. Click on OK. The L2TP Tunneling Security w indow

8. Click on OK. The L2TP IP Interf ace List w indow ope ns,

9. Set the following parameters:

• L2TP IP Interface Address

• Subnet Mask

10. Click on OK. You return to the L2TP IP Interface List

11. Click on OK.

Edit Circuit
Group Protocol s
Add/Delete
L2TP

RADIUS Client IP Address

Click on
descriptions beginning on page A-5.

Click on
descriptions beginning on page A-11.

Help

Help

. The Circuit Definition window opens.

. The Group Protocols menu opens.

. The Select Protocols window opens.

, then click on OK. The L2TP Configuration window opens.

or see the parameter

or see the param eter

The Edit Connector window opens.

opens.

followed by the L2TP IP Configuration
window.

Site Manager displays a message
alerting you of the time delay to create
the L2TP tunnel circuits.

window, which displays the IP interface
address and the subnet mask. A
message windo w opens that r eads,

Configuration is completed

L2TP

.

(continued)

300016-B Rev. 00

2-9

Configuring L2TP Services

Site Manager Procedure

You do this System responds

12. Click on

13.Choose

14.Choose

. You return to the Circuit Definition

Done

. The File menu opens.

File

. You return to the Configuration Manager

Exit

(continued)

window.

window.

If your ATM in terface uses an AT M connector, complete the following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

choose an ATM connector.

2. Choose

3. Choose

4. Choose

5. Choose

6. Complet e steps 6 through 11 in the

previous table.

7. Click on

8. Click on

9. Click on

Service Attributes

Protocols

Add/Delete.
L2TP

Done

Done

Done

. The Protocols menu opens.

, then click on OK. The L2TP Configuration window opens.

. You return to the ATM Service Records

. You return to the Edit ATM Connector

. You return to the Configuration Manager

. The ATM Service Records List window

The Edit ATM Connector window opens.

opens.

The Select Protocols window opens.

Site Manager enables L2TP.

List window.

window.

window.

2-10

300016-B Rev. 00

Chapter 3

Customizing L2TP Services

When you enable L2TP, default values are in effect for most parameters (see
parameter descriptions in Appendix A, “L2TP Parameters”). You may want to
change some of these values, depending on the requirements of your network.

This chapter includes the following information:

Topic Page

Modifying the L2TP Protocol Configuration 3-2
Modifying RADIUS Server Information 3-3
Changing th e LNS System Name 3-4
Modifying the Number of L2TP Sessio ns Permitted 3-5
Keeping the Remote User’s Domain Name 3-6
Changing th e Domain Name Delimiter 3-7
Enabling Tunnel Authentication 3-8
Modifying L2TP IP Interface Addresses 3-9
Disabling RIP 3-10
Disabling L2TP 3-10
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

300016-B Rev. 00

3-1

Configuring L2TP Services

Modifying the L2TP Protocol Configuration

To modify how data is transmitted across an L2TP network, such as the number,
frequency, and timing of data and acknowledgment packets exchanged between
the LNS and LAC, you can modify the L2TP protocol parameters.

To modify the L2TP protocol configuration, complete the following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Edit any of the following parameters:

• Receive Window Size

• Retransmit Timer (seconds)

• Maximum Retransmit

• Hello Timer (seconds)

• Ack Timeout (milliseconds)

•

7. Click on

Protocols

. The IP menu opens.

IP
L2TP

L2TP Configuration

Tunnel Flow Control

Click on
descriptions beginning on page A-3.

Done

.

. The L2TP menu opens.

. The L2TP Configuration List window

or see the param eter

Help

. You return to the Configuration Manager

The Protocols menu opens.

opens.

window.

3-2

300016-B Rev. 00

Modifying RADIUS Server Information

If you change the address of the RADIUS ser ver that you are using to aut hentica te
remote users and manage accounting functions, you must update the server
address information on the LNS.

For more information about using a RADIU S server in an L2TP network, see
“RADIUS Server” on page 1-6.

To modify the address of the RADIUS server, complete the following tasks:

Site Manager Procedure

You do this System responds

Customizing L2TP Servic es

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Set the following parameters:

• RADIUS Primary Server IP Address

• RADIUS Primary Server Password

•

7. Click on

Protocols

. The IP menu opens.

IP
L2TP

L2TP Configuration

RADIUS Client IP Address

Click on
descriptions beginning on page A-5.

Done

.

. The L2TP menu opens.

. The L2TP Configuration List window

or see the param eter

Help

. You return to the Configuration Manager

The Protocols menu opens.

opens.

window.

You can also modify the RADIUS information in the configuration windows
specific to RADIUS. For more information, see Configuring RADIUS.

300016-B Rev. 00

3-3

Configuring L2TP Services

Changing the LNS System Name

The LNS system name is the name of the router. This name is used during tunnel
setup to identify the LNS uniquely.

By default, Site Manager en ters the syste m name that you initially configured
when first accessing the router. See Configuring and Managing Routers with Site
Manager for more details about system information.

To change the LNS system name, complete the following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Set the

Click on
description on page A-5.

7. Click on

Protocols

. The IP menu opens.

IP
L2TP

L2TP Configuration

LNS System Name

Help

Done

.

. The L2TP menu opens.

. The L2TP Configuration List window

parameter.

or see the param eter

. You return to the Configuration Manager

The Protocols menu opens.

opens.

window.

3-4

300016-B Rev. 00

Customizing L2TP Servic es

Modifying the Number of L2TP Sessions Permitted

You can modify the maximum number of active L2TP sessions that the LNS can
manage. The default is 100 sessions.

For more information about L2TP sessions, see “L2TP Sessions” on page 1-3.
To change the maximum number of L2TP sessions supported by the LNS,

complete the following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Set the

Click on
description on page A-3.

7. Click on

Protocols

. The IP menu opens.

IP
L2TP

L2TP Configuration

Max L2TP Sessions

Help

Done

.

. The L2TP menu opens.

. The L2TP Configuration List window

parameter.

or see the param eter

. You return to the Configuration Manager

The Protocols menu opens.

opens.

window.

300016-B Rev. 00

3-5

Configuring L2TP Services

Keeping the Remote User’s Domain Name

The LNS removes the domain name from the complete user name by default,
before passing it on to the RADIUS server for user authentication.

To keep the domain name with the user name, complete the following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Set the

parameter to
see the param eter description on
page A-7.

7. Click on

Protocols

. The IP menu opens.

IP
L2TP

L2TP Configuration

Remove Domain Name

Done

.

. The L2TP menu opens.

. The L2TP Configuration List window

Disable

. Click on

. You return to the Configuration Manager

Help

or

The Protocols menu opens.

opens.

window.

3-6

300016-B Rev. 00

Changing the Domain Name Delimiter

In the complete user name there is a single-character delimiter that separates the
user name from the domain name. By default, the LNS remo ves the domain name
when it receives a call. The delimiter tells the LNS w hich charact ers to remove.
The default de limiter is an at sign (@).

To change the delimiter, complete the following tasks:

Site Manager Procedure

You do this System responds

Customizing L2TP Servic es

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Set the

parameter. Click on
parameter description on page A-7.

7. Click on

Protocols

. The IP menu opens.

IP
L2TP

L2TP Configuration

Domain Name Delimiter

Done

.

. The L2TP menu opens.

. The L2TP Configuration List window

or see the

Help

. You return to the Configuration Manager

The Protocols menu opens.

opens.

window.

300016-B Rev. 00

3-7

Configuring L2TP Services

Enabling Tunnel Authentication

To prevent unauthorized users from accessing the corporate network, you can
enable tunnel authentication. During tunnel negotiation, the LAC sends its tunnel
authentication password to the LNS. If the password is not recognized by the
LNS, authentication is unsuccessful and the LAC cannot create the tunnel.

Note:

If you are using the Password Authentication Protocol (PAP) for PPP

authentication, do not enable tunnel authentication.

For more informat ion about t unnel authent ication, see “ T unnel Auth entication ” on
page 1-12.

To enable tunnel authenticatio n, complete the following tasks:

Site Manager Procedure

You do this System responds

3-8

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Set the following parameters:

• Enable Tunnel Authentication

•

7. Click on

Protocols

. The IP menu opens.

IP
L2TP

Tunnel Authentication

Tunnel Authentication Password

Click on
descriptions on page A-9.

Done

.

. The L2TP menu opens.

. The L2TP Tunnel Security List window

or see the param eter

Help

. You return to the Configuration Manager

The Protocols menu opens.

opens.

window.

300016-B Rev. 00

Modifying L2TP IP Interface Addresses

The L2TP IP Interface List window lists the L2TP IP interface addresses for each
slot that has L2TP configured. The LNS uses the addresses internally to identify
the remote site s.

For more information about the L2TP IP interface, see “L2TP IP Interface
Addresses” on page 1-16.

To change an address on the list, complete the following tasks:

Site Manager Procedure

You do this System responds

Customizing L2TP Servic es

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Click on

7. Modify the following parameters:

• L2TP IP Interface Address

• Subnet Mask

8. Click on OK. You return to the L2TP IP Interface List

9. Click on

Protocols

. The IP menu opens.

IP
L2TP

L2TP IP Interface

Change

Click on
descriptions beginning on page A-11.

Done

.

. The L2TP menu opens.

. The L2TP IP Interface List window opens.

. The L2TP IP Interface window opens.

or see the parameter

Help

. You return to the Configuration Manager

The Protocols menu opens.

window. The new address appears in the
list.

window.

300016-B Rev. 00

3-9

Configuring L2TP Services

Disabling RIP

RIP is enabled on the LNS by default so that the LNS can learn routes from the
remote dial-in router. If the LNS does not require RIP support, you can disable it.

To disable RIP, complete the following tasks:

You do this System responds

Site Manager Procedure

1. In the Configuration Manager window,

choose

2. Choose

3. Choose

4. Choose

5. Select an LNS entry from the list.

6. Set the

Click on
description on page A-12.

7. Click on

Disabling L2TP

To dis able L2TP o n a slot, com plete the following tasks:

You do this System responds

1. In the Configuration Manager window,

choose

2. Choose IP. The IP menu opens.

3. Choose

4. Choose

5. Select an LNS entry from the list.

The Protocols menu opens.

Protocols

. The IP menu opens.

IP
L2TP

L2TP IP Interface

RIP Enable

Help

Done

Protocols

L2TP
L2TP Configuration

.

. The L2TP menu opens.

. The L2TP IP Interface List window opens.

parameter to

or see the parameter

. You return to the Configuration Manager

.

. The L2TP menu opens.

Disable

Site Manager Procedure

. The L2TP Configuration List window

.

window.

The Protocols menu opens.

opens.

(continued)

3-10

300016-B Rev. 00

Customizing L2TP Servic es

Site Manager Procedure

You do this System responds

6. Set the

Disable

parameter description on page A-3.

7. Click on

Enable L2TP

. Click on

Done

parameter to

or see the

Help

. You return to the Configuration Manager

Deleting L2TP from a PPP Interface

To delete L2TP from a PPP interface , complete the following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

click on a WAN connector configured with
L2TP.

2. Choose

3. Choose

4. Choose

5. Click on

6. Click on OK. You return to the Circuit Definition

7. Choose

8. Choose

Edit Circuit
Protocols
Add/Delete

L2TP

. The File menu opens.

File

. You return to the Configuration Manager

Exit

. The Circuit Definition window opens.

. The Protocols menu opens.

. The Select Protocols window opens.

. Site Manager deselects L2TP.

(continued)

Site Manager disables L2TP for the slot.

window.

The Edit Connector window opens.

window.

window.

300016-B Rev. 00

3-11

Configuring L2TP Services

Deleting L2TP from a Frame Relay Interface

To delete L2TP from a frame relay interface, com plete the following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

click on a WAN connector configured with
L2TP.

2. Choose

3. Choose

4. Choose

the window.

5. Choose

6. Click on

7. Click on OK. You return to the Frame Relay Service

8. Click on

9. Click on

Edit Circuit

Services

Protocols

Add/Delete

L2TP

Done

Done

. The Frame Relay Circuit D efinition

. The Frame Relay Servic e List window

in the top left corner of

. The Select Protocols window opens.

. Site Manager deselects L2TP.

. You return to the Frame Relay Circuit

. You return to the Configuration Manager

The Edit Connector window opens.

window opens.

opens.
The Protocols menu opens.

List window.

Definition window.

window.

3-12

300016-B Rev. 00

Deleting L2TP from an ATM Interface

To delete L2TP from an ATM interface on a COM connector, complete the
following tasks:

Site Manager Procedure

You do this System responds

Customizing L2TP Servic es

1. In the Configuration Manager window,

click on a COM connector configured with
L2TP.

2. Choose

3. Choose

4. Choose

5. Click on

6. Click on OK. You return to the Circuit Definition

7. Choose

8. Choose

Edit Circuit
Group Protocol s
Add/Delete

L2TP

. The File menu opens.

File

. You return to the Configuration Manager

Exit

. The Circuit Definition window opens.

. The Group Protocols menu opens.

. The Select Protocols window opens.

. Site Manager deselects L2TP.

The Edit Connector window opens.

window.

window.

To delete L2TP from an ATM interface on an ATM connector, complete the
following tasks:

Site Manager Procedure

You do this System responds

1. In the Configuration Manager window,

click on an ATM connector configured with
L2TP.

2. Choose

3. Choose

the window.

4. Choose

5. Click on

Service Attributes

Protocols

Add/Delete

L2TP

in the top left corner of

. The Select Protocols window opens.

. Site Manager deselects L2TP.

. The ATM Service Records List window

The Edit ATM Connector window opens.

opens.
The Protocols menu opens.

(continued)

300016-B Rev. 00

3-13

Configuring L2TP Services

Site Manager Procedure

You do this System responds

6. Click on OK. You return to the ATM Service Records

7. Click on

8. Click on

. You return to the Edit ATM Connector

Done

. You return to the Configuration Manager

Done

(continued)

List window.

window.

window.

3-14

300016-B Rev. 00

Appendix A

L2TP Parameters

This appendix contains the Site Manager parameter descriptions for L2TP
services. You can display the same information using Site Manager online Help.
For information about the IP parameters that you set when enabling L2TP, see
Configuring IP Services.

This appendix contains the following information:

Topic Page

300016-B Rev. 00

L2TP Configuration Parameters A-2
L2TP Tunnel Security Parameters A-8
L2TP IP Interface Parameters A-10

For each parameter, this appendix provid es the following information:

• Parameter name

• Configuration Manager menu path

• Default setting

• Valid parameter options

• Parameter function

• Instructions for setting the parameter

• Management information base (MIB) object ID

A-1

Configuring L2TP Services

The Technician Interface allows you to modify parameters by issuing set and

commit commands with the MIB object ID. This process is equivalent to

modifying parameters using Site Manager. For more information about using the
Technician Interface to access the MIB, see Using Technician Interface Software.

Caution:

The Technician Interface does not verify parameter values you enter.

Entering an invalid value can corrupt your configuration.

L2TP Configuration Parameters

The L2TP Configuration List window (Figure A-1) contains parameters that
define how L2TP sends and receives data.

A-2

Figure A-1. L2TP Configuration List Window

The parameter descriptions follow.

300016-B Rev. 00

L2TP Parameters

Parameter: Enable L2TP

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: Enable

Options: Enable

Disable

|

Function: Enables or disables L2TP on this interface.

Instructions: Site Manager aut omaticall y sets this paramete r to Enable when you se lect L2TP

as a protocol. Accept the default, Enable, to use L2TP. To temporarily disable
L2TP, set this parameter to Disable.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.2

Parameter: Max L2TP Sessions

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: 100

Options: 1 to 100 sessions

Function: Specifies the maximum number of L2TP sessions that the LNS allows.

Instructions: Enter the maximum number of L2TP se ssions that yo u want the LNS to supp ort.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.16

Parameter: Receive Window Size

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: 4

Options: 1 to 7 packets

Function: Specifies the number of control packets that the LNS can receive from the LAC

without the LNS sending an acknowledgment packet to the LAC.

Instructions: Enter the number of packets that determine the window size, or accept the

default value.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.6

300016-B Rev. 00

A-3

Configuring L2TP Services

Parameter: Retransmit Timer (seconds)

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: 1

Options: 1 to 60 seconds

Function: Indicates the number of seconds that the LNS waits for an acknowledgment

from the LAC before resending packets.

Instructions: If you are experiencing many timeouts during L2TP tunnel negotiation or

during a session, set this value to a number greater than the default. Otherwise,
accept the default.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.7

Parameter: Maximum Retransmit

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: 1

Options: 1 to 60

Function: Specifies the maximum number of times the LNS retransmits packets to the

LAC.

Instructions: If you are experiencing many timeouts during L2TP tunnel negotiation or

during a session, set this value to a number greater than the default. Otherwise,
accept the default.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.8

Parameter: Hello Timer (seconds)

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: 60

Options: 1 to 60 seconds

Function: Indicates the maximum number of seconds that can elapse without data activit y

before the LNS sends a packet through the tunnel to the LAC to check the
connection.

Instructions: Set this parameter to a smaller number only if the connection is not stable.

Otherwise, accept the default.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.9

A-4

300016-B Rev. 00

L2TP Parameters

Parameter: Ack Timeout (milliseconds)

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: 250

Options: 1 to 350 milliseconds

Function: Specifies the maximum number of milliseconds that can elapse before the LNS

sends an ackno wle dgment t o the LAC that it receiv e d an L2TP contr ol mess age,
such as a tunnel authentication or session control message.

Instructions: If you are unsure of the stability of the connection or the L2TP session, set this

parameter to a number smaller than the default. Otherwise, accept the default.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.10

Parameter: LNS System Name

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: BayRS

Options: The router’s system name or any name you specify

Function: Specifies the name of the LNS. This name applies to the router, not just the slot

with the LNS interface.

Instructions: Site Manager automatically enters the name from the router’s system

information. You can modify it, if you choose. If no system name is provided,
the router uses BayRS.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.12

Parameter: RADIUS Primary Server IP Address

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: None

Options: Any 32-bit IP address

Function: Specifies the primary RADIUS server for user authentication.

Instructions: Enter the IP address of the RADIUS server. If the RADIUS server is already

configured, Site Manager automatically supplies the address.

MIB Object ID: 1.3.6.1.4.1.18.3.5.22.2.1.3

300016-B Rev. 00

A-5

Configuring L2TP Services

Parameter: RADIUS Primary Server Password

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: None

Options: Any alphanumeric string, up to a maximum of 64 characters

Function: Specifies the primary RADIUS server’s password.

Instructions: Enter the password for the RADIUS server. If the RADIUS server is already

configured, Site Manager automatically supplies the password.

MIB Object ID: 1.3.6.1.4.1.18.3.5.22.2.1.11

Parameter: RADIUS Client IP Address

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: None

Options: Any IP address

Function: Identifi es t he router acting as the LNS. This address applies for the entire router.

Instructions: Enter the IP address of the router. If the RADIUS server is already configured,

Site Manager automatically supplies the address.

MIB Object ID: 1.3.6.1.4.1.18.3.5.22.1.1.5

Parameter: Tunnel Flow Control

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: Disable

Options: Enable

Disabl e

|

Function: Specifies wheth er the LNS us es flow control on the tunneled data packet s. Flo w

control ensures the stable flow of data between both sides of the connection.

Instructions: To enable flow control, select Enable. Otherwise, accept the default, Disable.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.20

A-6

300016-B Rev. 00

L2TP Parameters

Parameter: Remove Domain Name

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: Enable

Options: Enable

Disabl e

|

Function: Instructs the r out er whe the r to remove the domain name fr om t he complete user

name before RADIUS authentication takes place. If enabled, the LNS removes
the delimiter separating the user name and the domain name and all characters
to the right of the delimiter. Removing the domain name ensures that the
RADIUS server can identi fy the user with out having to reconfi gure the names in
the server database.

Instructions: Accept the default, Enable, to remove the domain name from the user name.

Select Disable to keep the domain name.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.21

Parameter: Domain Name Delimiter

Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration

Default: @

Options: A single-character string (for example, a colon)

Function: This character identifies the delimiter used to separate the domain name from

the user name. This parameter is relevant only if you accept the default value,
Enable, for the Remove Domain Name parameter.

Instructions: Specify a character as a delimiter or accept the default.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.2.1.22

300016-B Rev. 00

A-7

Configuring L2TP Services

L2TP Tunnel Security Parameters

The L2TP Tunnel Security List window (Figure A-2) contains the tunnel
authentication parameters.

A-8

Figure A-2. L2TP Tunnel Security List Window

The parameter descriptions follow.

300016-B Rev. 00

L2TP Parameters

Parameter: Enable Tunnel Authentication

Path: Configuration Manager > Protocols > IP > L2TP > Tunnel Authentication

Default: Disable

Options: Enable

Disable

|

Function: Enables or disables the use of tunnel authentication for a slot on the LNS.

Tunnel authentication provides a level of network security to protect the
corporate network from unauthorized users.

Instructions: Set this parameter to Enable for the LNS to perform tunnel authentication.

Otherwise, accept the default, Disable.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.1.1.2

Parameter: Tunnel Authentication Password

Path: Configuration Manager > Protocols > IP > L2TP > Tunnel Authentication

Default: None

Options: An alphanumeric string, up to a maximum of 40 characters

Function: Identifies t he LNS to the LA C if the de vices are us ing tunnel authenti cation. The

LAC and the LNS must share the same password to successfully complete
tunnel authentication.

Instructions: Enter a password.

MIB Object ID: 1.3.6.1.4.1.18.3.5.23.1.1.5

300016-B Rev. 00

A-9

Configuring L2TP Services

L2TP IP Interface Parameters

The L2TP IP Interface List window (Figure A-3) contains the list of IP interfaces
for each slot on the router configured with L2TP.

A-10

Figure A-3. L2TP IP Interface List Window

When you click on Change, Site Ma nag er displays the L2TP IP Interface windo w

(Figure A-4)

Figure A-4. L2TP IP Interface Window

.

300016-B Rev. 00

L2TP Parameters

The parameter descriptions follow.

Parameter: L2TP IP Interface Address

Path: Configuration Manager > Protocols > IP > L2TP > L2TP IP Interface

Default: None

Options: Any unique IP address

Function: Specifies the IP address that identifies the L2TP IP interface for the LNS. You

must provide an address for each slot configured as an LNS.

Instructions: Enter a unique IP address. This address applies for the entire router slot.

MIB Object ID: Not Applicable

Parameter: Subnet Mask

Path: Configuration Manager > Protocols > IP > L2TP > L2TP IP Interface

Default: None

Options: A 32-bit IP subnet mask

Function: Specifies the network and subnet portion of the L2TP IP interface address.

Site Manager automatically calculates a natural subnet mask based on the class
of the network address. For example, if you enter a Class C address, the subnet
mask will be 255.255.255.0.

To configure more subnets for your network, you can change this natural mask.

Instructions: Accept the assigned natural subnet mask or enter a new one. You are not

restricted to entering a natural mask. For example, if the L2TP IP address is

192.32.16.55, you can enter a subnet mask of 255.255.255.192.

MIB Object ID: 1.3.6.1.4.1.18.3.5.3.2.1.24.1.6

300016-B Rev. 00

A-11

Configuring L2TP Services

Parameter: RIP Enable

Path: Configuration Manager > Protocols > IP > L2TP > L2TP IP Interface

Default: Enable

Options: Enable

Disable

|

Function: Specifies whether RIP Listen is enabled on this interface. See Configuring IP

Services for more information about RIP.

Instructions: Accept the default, Enable, so that the LNS can learn routes from a remote

dial-in router. Select Disable to disable RIP.

MIB Object ID: 1.3.6.1.4.1.18.3.5.3.2.2.2.1.2

A-12

300016-B Rev. 00

Appendix B

Configuration Examples

This appendix provid es two e xamples of L2TP netw ork conf iguration s. It includes
only those parameters that require changes from their default settings for proper
configuration. For instructions on modifying parameters, see Chapter 3,
“Customizing L2TP Services.”

This appendix assumes th at you are fami liar with L2TP configuration procedures.
For information about setting up an interface on the router, see Quick-Starting
Routers and Configuring and Managing Routers with Site Manager.

Example 1: Remote PC Calling the Corporate Network

Figure B-1 shows a sample L2TP networ k. In this netw ork, note the following:

• Domain names are in the TMS database.

• User names and domain names are in the RADIUS server database.

• Tunnel IP interface addresses are unique for each slot.

• Frame relay is the WAN protocol for the connecti on between th e ISP netw ork
and the corporate network.

300016-B Rev. 00

B-1

Configuring L2TP Services

No active call from mmark;
no tunnel needed

[e-mail]

PC

No L2TP
functionality

[e-mail]

PC

No L2TP
functionality

Modem

TA

ISDN

Multilink
PPP

ISP network

LAC 2

TMS

LAC 1

Domain name in TMS database

baynetworks.com = 192.32.16.55

Frame rela y

T unnel

Corporate
network

LNS

192.32.16.55

192.32.68.2

L2TP IP
interface

IP addresses in the
RADIUS server database

192.32.40.1 [e-mail]

192.32.40.2 [e-mail]

Router

.17

RADIUS server

192.32.26.6
bay_private

.26.0

L2T0007B

Figure B-1. L2TP Network with PCs at the Remote Site

Configuring the Remote Hosts

The remote hosts in this network are two PCs running Windows® 95. Neither PC
has interna l L2TP capabilities.

In this network, one PC has a synchronous dial connection to the ISP via a
modem. The other PC has a 128 Kb/s dial ISDN connection through an ISDN
terminal adapter (TA).

The user names at the PCs ar e [e-mail] and
[e-mail].

B-2

300016-B Rev. 00

Configuring the LACs and the TMS

The LACs in this network are Model 5399 Remote Access Concentrators. Both
devices have L2TP modules installed. See Model 5399 Remote Access
Concentrator document ation for information about configuring L2TP.

The LACs use the same TMS, which you configure with the following
information:

Domain name: baynetworks.com
Tunnel end point address (LNS address): 192.32.16.55
Tunnel authentication password: LAC1

Configuring the LNS

The LNS in this network is a BN router with at least two synchronous interfaces.
To configure the router as an LNS:

1.

Choose a WAN port for the slot you want as the LNS.

2.

From the WAN Protocols menu, choose Frame Relay.

Configuration Examples

300016-B Rev. 00

3.

From the Select Protocols menu, choose IP and L2TP.

4.

In the IP Configuration window, enter the IP address of the LNS.

Parameter Name Value

IP Address 192.32.16.55

5.

In the L2TP Configuration window, enter the RADIUS server
information.

Parameter Name Value

RADIUS Primary Server IP A ddress 192.32.26.6
RADIUS Primary Server Password bay_private
RADIUS Client IP Address 192.32.16.55

B-3

Configuring L2TP Services

6.

In the L2TP Tunneling Security window, enable tunnel authenti cation.

Parameter Name Value

Enable Tunnel Authentication Enable
Tunnel Authentication Password LAC1

7.

In the L2TP IP Interface window, enter the L2TP IP address.

Parameter Name Value

L2TP IP Interface Address 192.32.68.2
Subnet Mask 255.255.255.0

During the L2TP session, the RADIUS server assigns the following IP
addresses:

[e-mail]: 192.32.40.1
[e-mail]: 192.32.40.2

These addresses are stored in the RADIUS server database.

Data Path Through the Network

After all components of the network are configured, jsmart can place a call to the
local ISP. The LAC that receives this call sends the user name to the TMS, which
verifie s the domain name and address and sends t hi s i nf ormat i on back to the LAC
so that it can forward the data.

The LAC then negotiates the initiation of the tunnel with the LNS, and the tunnel
is brought up. The LNS then authenticates [e-mail] with the
RADIUS server. After the RADIUS server grants access, it assigns the address

192.32.40.1 to jsmart, to include the remote host (jsmart’s PC) in the virtual
private network.

Data now passes through the tunnel from jsmart’s PC to the LNS for the duration
of the L2TP session. When jsmart disconnects the call, the session is terminated.
If no other active sessions are using the tunnel, the tunnel is brought down.

B-4

300016-B Rev. 00

Configuration Examples

Example 2: Remote Router Calling the Corporate Network

Figure B-2 shows a netwo rk wi th two BayStack™ AN® routers at the remote site.

The AN routers are using dial-on-demand service for dial-up connections.
In this network, note the following:

• PPP is the WAN protocol fo r the connection between the ISP net w ork and the
corporate network.

• For the LNS configuration, you do not need to configure a static route for the
remote router’s network because the LNS can learn the route using RIP.

• The IP network addresses are assigned as follows:
[e-mail]: 192.32.40.1
[e-mail]: 192.32.40.2

No active call from mmark;

PC

PC

no tunnel needed

mmark@bay .com

No L2TP
functionality

jsmart@bay .com

No L2TP
functionality

Modem

TA

ISDN

Multilink
PPP

ISP network

LAC 2

TMS

LAC 1

Domain name in TMS database

bay .com = 192.32.16.55

LNS

192.32.16.55

PPP

T unnel

192.32.40.254

L2TP IP
interface

IP addresses in the
RADIUS server database

192.32.40.1 jsmart@bay .com

192.32.40.2 mmark@bay .com

Corporate
network

.17

RADIUS server

192.32.26.6
bay_private

Router

.26.0

L2T0008B

Figure B-2. L2TP Network with Routers at the Remote Site

The LNS configu ration i n thi s e xam ple is the s ame as i n Exampl e 1; however , yo u
must modify the configuration of the remote AN router. Go to the next sections.

300016-B Rev. 00

B-5

Configuring L2TP Services

Configuring the Dial-on-Demand Circuit

Modify the dial-on-dem and circuit configuration for the AN routers as foll ows:

1.

In the Configurati on Manager window, choose Dialup > Demand Circuits
> Demand Pools > PPP Circuits > PPP Demand Circuits to display the
PPP Demand Circuits window.

2.

Disable outbound authentication.

Parameter Name Value

Outbound Authentication Disable
CHAP Local Name [e-mail]
Dial Optimized Routing Enabled

3.

Enable RIP on the dial-on-demand circuit.

4.

Configure default or static routes for the PC LAN to the L2TP IP
interface.

For more inform ation about dial-on-demand, see Configuring Dial Services.

Configuring the PPP Interface

Modify the PPP interface configuration for the AN routers as follows:

1.

In the Configuration Manager window, choose Protocols > PPP >
Interfaces to display the PPP Interface List window.

2.

Select the PPP interface to the ISP network.

3.

Click on Lines to display the PPP Line List window.

4.

Enable RFC 1661 compliance.

Parameter Name Value

RFC1661 Compliance Enable

For more inform ation about PPP, see Configuring PPP Servi ces.

B-6

300016-B Rev. 00

Appendix C

Troubleshooting

T o monitor your L2TP netw ork and solv e problems tha t may occur , f irs t check the
event log file for any messages recorded by the LNS. For information about
viewing and reading event messages, see Event Messages for Rou t ers and
Configuring and Managing Routers with Site Manager.

Table C-1

provides troubleshooting solutions for common problems with your

L2TP network.

Table C-1. Common L2TP Network Problems and Solutions

Problem What to Do

L2TP tunnel did not initiate. Check whether you enabled tunnel authentication for

the LNS on that slot.
If authentication is enabled, make sure that the

authentication pass w ord is th e same f or the LA C and
the LNS.

You can also check the tunnel statistics, which are
automatically enabled on the LNS.

L2TP host (PC or router) cannot
reach the corporate network
through the established
connection.

Check the address and user authentication
information configured in the RADIUS server
database.

(continued)

300016-B Rev. 00

C-1

Configuring L2TP Services

Table C-1. Common L2TP Network Problems and Solutions

Problem What to Do

L2TP session is not active. The LNS failed to negotiate the PPP LCP options.

Reconfigure the host at the remote site dialing in to
the ISP.

For a Bay Networks router at the remote site, check
the PPP MRU/MRRU size. The LNS supports an
MRU/MRUU size of 1500 only.

Use the following guidelines to configure a Bay
Networks router at the remote site:

• For router software versions up to and including

11.02/rel, use an MTU size of 1510, which is the
default.

• For router software versions 11.02/rev and later

Bay Netwo rks router at t he remote
site cannot tunnel into the
corporate network.

set the PPP parameter
Enable.

You can also check the session statistics, which are
automatically enabled on the LNS.

Check the IP address assigned by the RADIUS
server. There may be a mismatch between the
address of the remote router dialing in to the LAC
and the address that the RADIUS server assigns.

RFC1661 Complianc e

(continued)

to

C-2

For example, router A dials in with its IP address of

1.1.1.3 and the RADIUS server assigns an incorrect
IP address of 1.1.1.5.

300016-B Rev. 00

Index

A

accounting, RADIUS, 1-15
Ack Timeout (milliseconds) parameter, A-5

B

Bay Networks LNS. See LNS

C

configuratio n examples, B-1
configuration file, requirements, 2-3
customer support

programs, xvi
Technical Solutions Centers, xvii

D

deleting L2TP

from ATM, 3-13
from frame relay, 3-12

from PPP, 3-11
disabling L2TP, 3-10
Domain Name Delimiter parameter, A-7
domain name, description, 1-12

E

Enable L2TP parameter, A-3
Enable Tunnel Authentication parameter, A-9

H

Hello Timer (seconds) parameter, A-4

L

L2TP

Bay Networks implem e ntatio n, 1-11
customizing configuration, 3-1
data transmission across network, 1-9
deleting, ATM interface, 3-13
deleting, frame relay interface, 3-12
deleting, PPP interface, 3-11
description, 1-1
disabling, 3-10
network components, 1-4
packet encapsulation, 1-8
parameter descript ions, A-1
parameters, modifying, 3-2
purpose, 1-2
starting, 2-3

troubleshootin g, C-1
L2TP access concentrator. See LAC
L2TP IP Interface Address parameter, A-11
L2TP IP interface address, modifyin g, 3-9
L2TP network server. See LNS
LAC

configuration example, B-3

description, 1-5

tunnel authentication, security, 1-12
Layer 2 Tunneling Protocol. See L2TP
LNS

Bay Networks implem e ntatio n, 1-11

changing RADIUS server address, 3-3

changing system name, 3- 4

configuration example, B-3

configuring router as, 2- 3

customizing parameters, 3-1

description, 1-6

enabling tunnel authenticatio n, 3-8

300016-B Rev. 00

Index-1

LNS (continued)

L2TP security, 1-10
modifying protocol configuration, 3-2

operating with LA Cs, 1-1 1
LNS System Name parameter, A-5
LNS system name, changing, 3-4

S

sessions, L2TP

description, 1-3
modifying number permitted, 3-5

Subnet Mask parameter, A-11

M

Max L2TP Sessions parameter, A-3
Maximum Retransmit parameter, A-4

P

packet encapsulation, L2TP, 1-8
parameters

customizing, 3-1

descriptions, A-1

See also parameter names

password, RADIUS server

description, 1-14

setting, 3-3
password, tunnel authe ntica tio n

description, 1-12

setting, 3-8

R

RADIUS Client IP Address parameter, A-6
RADIUS Primary Server IP Address parameter, A-5
RADIUS Primary Server Password parameter, A-6
RADIUS server

changing address and password, 3-3

description, 1-6

for user authentication, 1-14
Receive Window Size parameter, A-3
remote access server (RAS), 1-5
Remove Domain Name parameter, A-7
Retransmit Timer (seconds) parameter, A-4
RIP Enable parameter, A-12
router platforms for L2TP, 1-11

T

Technical Solutions Centers, xvii
TMS, description, 1-5, 1-12
troubleshootin g network problems, C-1
tunnel authentica tion

description, 1-12

enabling, 3-8
Tunnel Authentication Password parameter, A-9
Tunnel Flow Control parameter, A-6
tunnel manage ment server. See TMS
tunnel, description, 1-2

U

user authentication, RADIUS, 1-14

V

virtual private network (VPN), d escription, 1-1

Index-2

300016-B Rev. 00