Nortel Networks Network Router L2TP User Manual

Configuring  
L2TP Services  
BayRS Version 13.00  
Site Manager Software Version 7.00  
Part No. 303532-A Rev 00  
October 1998  
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Contents  
Preface  
Before You Begin .............................................................................................................xiii  
Acronyms ......................................................................................................................... xv  
L2TP Overview  
Bay Networks L2TP Implementation ............................................................................1-11  
Tunnel Management ...............................................................................................1-12  
Tunnel Authentication .............................................................................................1-12  
RADIUS User Authentication .................................................................................1-14  
RADIUS Accounting ...............................................................................................1-15  
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L2TP IP Interface Addresses .................................................................................1-15  
Starting L2TP  
Preparing a Configuration File ........................................................................................2-3  
Enabling L2TP on an Existing PPP Interface .................................................................2-5  
Customizing L2TP Services  
Disabling RIP ................................................................................................................3-10  
Deleting L2TP from a PPP Interface .............................................................................3-11  
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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Configuration Examples  
Configuring the LNS ................................................................................................ B-3  
Example 2: Remote Router Calling the Corporate Network .......................................... B-5  
Configuring the PPP Interface ................................................................................. B-6  
Appendix C  
Troubleshooting  
Index  
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Figures  
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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Tables  
Table C-1.  
Common L2TP Network Problems and Solutions .................................. C-1  
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Preface  
This guide describes Layer 2 Tunneling Protocol (L2TP) and what you do to start  
and customize L2TP services on a Bay Networks® router.  
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-Starting Routers, Configuring BayStack Remote Access, or Connecting  
ASN Routers to a Network).  
Make sure that you are running the latest version of Bay Networks BayRSand  
Site Manager software. For information about upgrading BayRS and Site  
Manager, see the upgrading guide for your version of BayRS.  
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Configuring L2TP Services  
Text Conventions  
This guide uses the following text conventions:  
bold text  
Indicates text that you need to enter and command  
names and options.  
Example: Enter  
{
|
}
show ip alerts routes  
Example: Use the command.  
dinfo  
italic text  
Indicates file and directory names, new terms, book  
titles, and variables in command syntax descriptions.  
Where a variable is two or more words, the words are  
connected by an underscore.  
Example: If the command syntax is:  
<valid_route>  
show at  
valid_route is one variable and you substitute one value  
for it.  
screen text  
separator ( > )  
Indicates system output, for example, prompts and  
system messages.  
Example: Set Bay Networks Trap Monitor Filters  
Shows menu paths.  
Example: Protocols > IP identifies the IP option on the  
Protocols menu.  
vertical line ( | )  
Separates choices for command keywords and  
arguments. Enter only one of the choices. Do not type  
the vertical line when entering the command.  
Example: If the command syntax is:  
{
|
}, you enter either:  
show ip alerts routes  
or  
, but not both.  
show ip alerts show ip routes  
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Preface  
Acronyms  
CHAP  
IP  
Challenge Handshake Authentication Protocol  
Internet Protocol  
ISDN  
ISP  
Integrated Services Digital Network  
Internet Service Provider  
L2TP  
LAC  
Layer 2 Tunneling Protocol  
L2TP access concentrator  
local area network  
LAN  
LCP  
Link Control Protocol  
LNS  
L2TP network server  
MPPP  
PAP  
Multilink Point-to-Point Protocol  
Password Authentication Protocol  
Point-to-Point Protocol  
PPP  
RADIUS  
RAS  
Remote Authentication Dial-In User Service  
remote access server  
RIP  
Routing Information Protocol  
start control connection connected  
start control connection reply  
start control connection request  
terminal adapter  
SCCCN  
SCCRP  
SCCRQ  
TA  
TCP/IP  
TMS  
UDP  
Transmission Control Protocol/Internet Protocol  
tunnel management server  
User Datagram Protocol  
VPN  
WAN  
virtual private network  
wide area network  
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Configuring L2TP Services  
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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 infrastructure of a public  
network, such as the Internet, but offers the security and exclusivity of a private  
network.  
This chapter contains the following information:  
Topic  
Page  
L2TP Benefits  
1-2  
What Is Tunneling?  
1-2  
Components of an L2TP Network  
L2TP Packet Encapsulation  
Making a Connection Across an L2TP Network  
Security in an L2TP Network  
Bay Networks L2TP Implementation  
Where to Go Next  
1-4  
1-8  
1-9  
1-10  
1-11  
1-17  
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Configuring L2TP Services  
L2TP Benefits  
L2TP has several advantages:  
Users and businesses can take advantage of existing network equipment and  
resources.  
Corporations do not need to maintain and manage remote access servers and  
other special networking equipment for remote users. Instead, they can use  
their existing Internet leased connections and resources at the Internet Service  
Provider (ISP) network, thereby significantly reducing corporate networking  
and maintenance costs.  
In addition, corporations do not need to provide technical support to the  
remote users. Because the remote user is making a local call to the ISP, the  
ISP provides technical assistance if the user has trouble making connections.  
Remote users can place a free local call to their ISP for access to the Internet,  
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-based protocol that provides greater interoperability with  
networking equipment from other vendors.  
What Is Tunneling?  
Tunneling is a way of forwarding traffic from remote users to a corporate network  
through an IP network. A tunnel is a virtual connection between two sites, for  
example, an access concentrator at the ISP network 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.  
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L2TP Overview  
Multiple users can communicate through a single tunnel between the same LAC  
and LNS pair. Each user transmits and receives data in an individual L2TP  
session.  
The LAC brings down the tunnel for any one of the following reasons:  
A network failure occurs.  
The LAC or other equipment at the ISP is not operating properly. If the LAC  
fails, all tunnel users are disconnected.  
There are no active sessions inside the tunnel.  
An individual session ends when a remote user disconnects the call, but  
multiple sessions can run inside a single tunnel.  
The system administrator at the ISP terminates the user connection.  
The LAC is not responding to a Hello packet from the LNS.  
For the LAC to reestablish a tunnel, the remote user has to place a new call.  
L2TP Sessions  
Packets are exchanged across an L2TP tunnel during an L2TP session. An L2TP  
session is created when an end-to-end WAN connection is established between the  
remote host and the LNS.  
The L2TP portion of the packets sent through the tunnel contains a header with a  
call ID field (also called a session ID) and a tunnel ID field. The call ID field,  
which indicates the session that the WAN packet belongs to, is negotiated between  
the LAC and the LNS when the L2TP call is set up. The tunnel ID specifies the  
tunnel that the L2TP session is using.  
In addition to the fields in the header, the L2TP packet contains a call serial  
number, which is a unique number for each L2TP call. This number matches the  
call to the L2TP session.  
For an L2TP session, you can enable flow control. Flow control manages  
congestion across the connection, ensures that packets are not lost, and makes sure  
the devices at each end of the connection are communicating properly.  
To enable flow control, see Chapter 3, “Customizing L2TP Services.”  
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Configuring L2TP Services  
Components of an L2TP Network  
The following sections describe the components of an L2TP network. For  
illustrations of L2TP networks, see Figures 1-1 and 1-2 on page 1-7.  
Remote Host  
At the remote site is the user who wants to dial in to the corporate network. The  
remote user can be located anywhere, provided that the user can dial into an ISP  
network using a PC or a router. The ISP provides the connection to the Internet.  
The host at the remote site can be a PC or router that uses PPP for dial-up  
connections.  
If the PC or router does not have built-in L2TP software capabilities, it dials  
into a LAC, which provides a tunnel across the Internet to the corporate LNS.  
If the PC or router is an L2TP client, that is, it has built-in L2TP functionality,  
the L2TP client software provides a tunnel through a RAS across the Internet  
to the corporate LNS. A LAC is unnecessary with an L2TP client.  
The main difference between connecting an L2TP client and a nonclient is the  
starting point of the tunnel. For an L2TP client, the tunnel begins at the PC or  
router; for a non-L2TP client, the tunnel begins at the LAC. All tunnels end at the  
LNS.  
Note: This guide’s primary focus is on an L2TP network between a remote  
host that does not have built-in L2TP capabilities and uses a LAC, rather than a  
RAS.  
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L2TP Overview  
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 server with 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 information about the Bay Networks implementation of the LAC in an  
L2TP network, see “Bay Networks L2TP Implementation” on page 1-11.  
Remote Access Server (RAS)  
The remote access server (RAS) resides at the ISP network. If the remote host is  
an L2TP client, the tunnel is established from the remote client through a RAS to  
an LNS at the corporate network. In this situation, there is no need for a LAC.  
The RAS does not establish the tunnel; it only forwards already tunneled data to  
the destination.  
Tunnel Management Server (TMS)  
At the ISP network, there needs to be a mechanism for identifying L2TP tunneled  
users so that the LAC can construct the L2TP tunnel. Bay Networks uses a  
mechanism called a tunnel management server (TMS); other vendors may use a  
different method.  
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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 connection request and allows 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 multiple remote users, each communicating within their 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 L2TP Implementation” on page 1-11.  
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:  
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 configure each LNS with user names and passwords. It also assigns an  
IP address to a remote host to identify the host. Finally, the RADIUS server can  
provide accounting services for the corporate network, calculating billing charges  
for an L2TP session.  
For information about the Bay Networks implementation of RADIUS user  
authentication and accounting, see “RADIUS User Authentication” on page 1-14  
and “RADIUS Accounting” on page 1-15.  
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L2TP Overview  
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  
Frame relay  
connection  
Corporate network  
LNS  
Remote  
host  
LAC  
Tunnel  
PPP  
connection  
PC  
Data  
TMS  
RADIUS  
server  
No L2TP  
functionality  
L2T0003A  
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  
Frame relay  
connection  
Corporate network  
LNS  
Remote  
host  
RAS  
Tunnel  
PC  
Data  
RADIUS  
server  
L2TP  
client  
L2T0004A  
Figure 1-2.  
L2TP Network Using a RAS  
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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 shows how data is encapsulated for transmission over an L2TP  
network.  
Remote user places a call  
PPP  
IP  
DATA  
LAC  
Layer 2  
protocol  
PPP  
IP/UDP L2TP  
IP  
DATA  
LNS  
DATA  
IP  
Data packet moves to the corporate network  
L2T0005A  
Figure 1-3.  
Packet Encapsulation Process  
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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 on page 1-7):  
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 includes 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, [email protected]; 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.  
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 tunnel is established, 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 is successfully authenticated, the user has an end-to-end  
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.  
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Configuring L2TP Services  
Security in an L2TP Network  
You can configure two layers of security in an L2TP network:  
Tunnel authentication  
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 the 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 whether 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 Authentication” on page 1-12 and “RADIUS User  
Authentication” on page 1-14.  
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L2TP Overview  
Bay Networks L2TP Implementation  
In an L2TP network, the Bay Networks router is the LNS. LNS software operates  
on the BLN®, BCN®, and ASNplatforms.  
The Bay Networks LNS has the following characteristics:  
Each slot can act as an LNS, which means that one router can have many LNS  
interfaces, each with its own address. You can have as many LNS interfaces 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 on page 1-7) is a leased line operating with frame relay, PPP  
(including PPP multilink), or ATM. Bay Networks recommends that you use a  
high-speed link, such as T1, for the leased connection.  
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.”  
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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 portion of the user’s address that specifies a particular location  
in the network. For example, if the user name is [email protected],  
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 follow a specific format. It is not related to any Domain Name System  
(DNS) protocol requirements.  
Tunnel Authentication  
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 client 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 Authentication Protocol (CHAP). When one side receives a challenge,  
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.  
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L2TP Overview  
You can enable tunnel authentication on the Bay Networks LNS. If tunnel  
authentication is disabled, which is the default, the LNS sends a default challenge  
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) message 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.  
Figure 1-4 shows tunnel authentication.  
ISP network  
Corporate network  
PPP connection  
LNS  
LAC  
SCCRQ  
tunnel request and challenge  
SCCRP  
tunnel response, challenge response,  
and LNS challenge  
SCCCN  
challenge response  
L2T0006A  
Figure 1-4.  
Tunnel Authentication Control Messages  
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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 authentication is enabled by default on the Bay Networks LNS; you  
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 receives 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.  
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  
automatically removes the domain portion of the user name that is included as part  
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 information about configuring Bay Networks routers as RADIUS  
servers, see Configuring RADIUS.  
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L2TP Overview  
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 these charges, the server 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 charges, which the network administrator can use to manage network costs.  
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.  
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 by 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.  
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Configuring L2TP Services  
Remote Router Configuration  
If the host at the remote site is a Bay Networks router, you may need to configure  
a dial-on-demand circuit for the remote router’s dial-up interface 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 routing information from the remote  
router. To avoid unnecessarily activating the circuit because of RIP packets,  
enable dial-optimized routing for the dial-on-demand circuit (see Figure 1-5).  
In addition, configure a default or static route for the remote router, which uses 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.  
LAC  
192.168.18.41  
PC 1  
LNS  
192.168.19.34  
Dial-in router  
192.32.25.34  
PC 2  
L2TP IP, RIP enabled  
192.32.33.94  
192.32.25.35  
LAN interface Dial-on-demand  
RIP enabled RIP enabled  
192.32.25.33 Dial-optimized  
routing enabled  
192.32.25.66  
L2T0009B  
Figure 1-5.  
Remote Router Dialing the LNS  
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L2TP Overview  
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.  
Change default settings for L2TP parameters.  
Chapter 2  
Chapter 3  
Appendix A  
Obtain information about Site Manager parameters (this is the same  
information you obtain using Site Manager online Help).  
Review configuration examples.  
Appendix B  
Appendix C  
Troubleshoot L2TP configuration problems.  
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Chapter 2  
Starting L2TP  
The quickest way to start L2TP is to enable 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 have default  
values.  
This chapter includes the following information:  
Topic  
Page  
Planning Considerations for an L2TP Network  
Preparing a Configuration File  
2-2  
2-3  
2-4  
2-5  
2-7  
2-9  
Enabling L2TP on an Unconfigured WAN Interface  
Enabling L2TP on an Existing PPP Interface  
Enabling L2TP on an Existing Frame Relay Interface  
Enabling L2TP on an Existing ATM Interface  
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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.  
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:  
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 only way to assign  
addresses is by the RADIUS server. This address is also used for network  
communication across the subscriber network.  
For more information about configuring Bay Networks routers as RADIUS  
servers, see Configuring RADIUS.  
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Starting L2TP  
Preparing a Configuration 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.  
Note: L2TP is not compatible with dial services. Do not enable L2TP on the  
same slot that you enable for a dial service, such as dial-on-demand, dial  
backup, or bandwidth-on-demand.  
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  
1. In the main Site Manager window, choose The Tools menu opens.  
Tools.  
2. Choose Configuration Manager.  
The Configuration Manager window  
opens.  
3. Choose Local File, Remote File, or  
Site Manager prompts you for the  
configuration file you want to open.  
Dynamic.  
4. Select the file and click on OK.  
The Configuration Manager window  
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  
Enabling L2TP on an Existing Frame Relay Interface  
Enabling L2TP on an Existing ATM Interface  
2-4  
2-5  
2-7  
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Configuring L2TP Services  
Enabling L2TP on an Unconfigured WAN Interface  
To enable L2TP on an unconfigured WAN interface, complete the following tasks:  
Site Manager Procedure  
You do this  
System responds  
1. In the Configuration Manager window,  
choose a WAN connector.  
The Add Circuit window opens.  
2. Accept the default circuit name or change The WAN Protocols window opens.  
it, then click on OK.  
3. Choose PPP, Frame Relay, or ATM then The Select Protocols window opens.  
click on OK.  
4. Choose L2TP, then click on OK.  
The IP Configuration window opens.  
The L2TP Configuration window opens.  
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  
RADIUS Client IP Address  
Click on Help or see the parameter  
descriptions beginning on page A-5.  
7. Click on OK.  
The L2TP Tunneling Security window  
opens.  
8. Click on OK.  
The L2TP IP Interface List window opens,  
followed by the L2TP IP Configuration  
window.  
9. Set the following parameters:  
Site Manager displays a message  
alerting you of the time delay to create  
the L2TP tunnel circuits.  
L2TP IP Interface Address  
Subnet Mask  
Click on Help or see the parameter  
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 window opens that reads, L2TP  
Configuration is completed.  
(continued)  
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Starting L2TP  
Site Manager Procedure (continued)  
You do this  
System responds  
11. Click on OK.  
12. Click on Done.  
You return to the Configuration Manager  
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.  
The Edit Connector window opens.  
2. Choose Edit Circuit.  
The Circuit Definition window opens.  
3. Choose Protocols in the top left corner of The Protocols menu opens.  
the window.  
4. Choose Add/Delete.  
The Select Protocols window opens.  
The L2TP Configuration window opens.  
5. Choose L2TP, then click on OK.  
6. Set the following parameters:  
RADIUS Primary Server IP Address  
RADIUS Primary Server Password  
RADIUS Client IP Address  
Click on Help or see the parameter  
descriptions beginning on page A-5.  
7. Click on OK.  
The L2TP Tunneling Security window  
opens.  
8. Click on OK.  
The L2TP IP Interface List window opens,  
followed by the L2TP IP Configuration  
window.  
(continued)  
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Configuring L2TP Services  
Site Manager Procedure (continued)  
You do this  
System responds  
9. Set the following parameters:  
Site Manager displays a message  
L2TP IP Interface Address  
Subnet Mask  
alerting you of the time delay to create  
the L2TP tunnel circuits.  
Click on Help or see the parameter  
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 window opens that reads, L2TP  
Configuration is completed.  
11. Click on OK.  
12. Click on Done.  
You return to the Circuit Definition  
window.  
13. Choose File.  
The File menu opens.  
14. Choose Exit.  
You return to the Configuration Manager  
window.  
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Starting L2TP  
Enabling L2TP on an Existing Frame Relay Interface  
To enable L2TP on an interface with frame relay 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.  
The Edit Connector window opens.  
2. Choose Edit Circuit.  
The Frame Relay Circuit Definition  
window opens.  
3. Choose Services.  
The Frame Relay Service List window  
opens.  
4. Choose Protocols in the top left corner of The Protocols menu opens.  
the window.  
5. Choose Add/Delete.  
The Select Protocols window opens.  
The L2TP Configuration window opens.  
6. Choose L2TP, then click on OK.  
7. Set the following parameters:  
RADIUS Primary Server IP Address  
RADIUS Primary Server Password  
RADIUS Client IP Address  
Click on Help or see the parameter  
descriptions beginning on page A-5.  
8. Click on OK.  
The L2TP Tunneling Security window  
opens.  
9. Click on OK.  
The L2TP IP Interface List window opens,  
followed by the L2TP IP Configuration  
window.  
10. Set the following parameters:  
Site Manager displays a message  
alerting you of the time delay to create  
the L2TP tunnel circuits.  
L2TP IP Interface Address  
Subnet Mask  
Click on Help or see the parameter  
descriptions beginning on page A-11.  
(continued)  
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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 window opens that reads, L2TP  
Configuration is completed.  
12. Click on OK.  
13. Click on Done.  
You return to the Frame Relay Service  
List window.  
14. Click on Done.  
You return to the Frame Relay Circuit  
Definition window.  
15. Click on Done.  
You return to the Configuration Manager  
window.  
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Starting L2TP  
Enabling L2TP on an Existing ATM Interface  
To enable L2TP on an interface with ATM and IP already enabled, you can enable  
L2TP in two ways. If your interface uses a COM connector, complete the tasks in  
the following table. If your interface uses an ATM connector, go to page 2-10.  
Site Manager Procedure  
You do this  
System responds  
1. In the Configuration Manager window,  
choose a WAN connector.  
The Edit Connector window opens.  
2. Choose Edit Circuit.  
The Circuit Definition window opens.  
The Group Protocols menu opens.  
The Select Protocols window opens.  
The L2TP Configuration window opens.  
3. Choose Group Protocols.  
4. Choose Add/Delete.  
5. Choose L2TP, then click on OK.  
6. Set the following parameters:  
RADIUS Primary Server IP Address  
RADIUS Primary Server Password  
RADIUS Client IP Address  
Click on Help or see the parameter  
descriptions beginning on page A-5.  
7. Click on OK.  
The L2TP Tunneling Security window  
opens.  
8. Click on OK.  
The L2TP IP Interface List window opens,  
followed by the L2TP IP Configuration  
window.  
9. Set the following parameters:  
Site Manager displays a message  
alerting you of the time delay to create  
the L2TP tunnel circuits.  
L2TP IP Interface Address  
Subnet Mask  
Click on Help or see the parameter  
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 window opens that reads, L2TP  
Configuration is completed.  
11. Click on OK.  
(continued)  
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Configuring L2TP Services  
Site Manager Procedure (continued)  
You do this  
System responds  
12. Click on Done.  
You return to the Circuit Definition  
window.  
13. Choose File.  
The File menu opens.  
14. Choose Exit.  
You return to the Configuration Manager  
window.  
If your ATM interface uses an ATM connector, complete the following tasks:  
Site Manager Procedure  
You do this  
System responds  
1. In the Configuration Manager window,  
choose an ATM connector.  
The Edit ATM Connector window opens.  
2. Choose Service Attributes.  
The ATM Service Records List window  
opens.  
3. Choose Protocols.  
The Protocols menu opens.  
4. Choose Add/Delete.  
The Select Protocols window opens.  
The L2TP Configuration window opens.  
Site Manager enables L2TP.  
5. Choose L2TP, then click on OK.  
6. Complete steps 6 through 11 in the  
previous table.  
7. Click on Done.  
8. Click on Done.  
9. Click on Done.  
You return to the ATM Service Records  
List window.  
You return to the Edit ATM Connector  
window.  
You return to the Configuration Manager  
window.  
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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.  
Topic  
Page  
Modifying the L2TP Protocol Configuration  
Modifying RADIUS Server Information  
Changing the LNS System Name  
Modifying the Number of L2TP Sessions Permitted  
Keeping the Remote User’s Domain Name  
Changing the Domain Name Delimiter  
Enabling Tunnel Authentication  
3-2  
3-3  
3-4  
3-5  
3-6  
3-7  
3-8  
Modifying L2TP IP Interface Addresses  
Disabling RIP  
3-9  
3-10  
3-10  
3-11  
3-12  
3-13  
Disabling L2TP  
Deleting L2TP from a PPP Interface  
Deleting L2TP from a Frame Relay Interface  
Deleting L2TP from an ATM Interface  
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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,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP Configuration.  
The L2TP Configuration List window  
opens.  
6. Edit any of the following parameters:  
Receive Window Size  
Retransmit Timer (seconds)  
Maximum Retransmit  
Hello Timer (seconds)  
Ack Timeout (milliseconds)  
Tunnel Flow Control  
Click on Help or see the parameter  
descriptions beginning on page A-3.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
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Customizing L2TP Services  
Modifying RADIUS Server Information  
If you change the address of the RADIUS server that you are using to authenticate  
remote users and manage accounting functions, you must update the server  
address information on the LNS.  
For more information about using a RADIUS 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  
1. In the Configuration Manager window,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP Configuration.  
The L2TP Configuration List window  
opens.  
5. Select an LNS entry from the list.  
6. Set the following parameters:  
RADIUS Primary Server IP Address  
RADIUS Primary Server Password  
RADIUS Client IP Address  
Click on Help or see the parameter  
descriptions beginning on page A-5.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
You can also modify the RADIUS information in the configuration windows  
specific to RADIUS. For more information, see Configuring RADIUS.  
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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 enters the system 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,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP Configuration.  
The L2TP Configuration List window  
opens.  
5. Select an LNS entry from the list.  
6. Set the LNS System Name parameter.  
Click on Help or see the parameter  
description on page A-5.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
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Customizing L2TP Services  
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,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP Configuration.  
The L2TP Configuration List window  
opens.  
5. Select an LNS entry from the list.  
6. Set the Max L2TP Sessions parameter.  
Click on Help or see the parameter  
description on page A-3.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
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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,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP Configuration.  
The L2TP Configuration List window  
opens.  
5. Select an LNS entry from the list.  
6. Set the Remove Domain Name  
parameter to Disable. Click on Help or  
see the parameter description on  
page A-7.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
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Customizing L2TP Services  
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 removes the domain name  
when it receives a call. The delimiter tells the LNS which characters to remove.  
The default delimiter is an at sign (@).  
To change the delimiter, complete the following tasks:  
Site Manager Procedure  
You do this  
System responds  
1. In the Configuration Manager window,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP Configuration.  
The L2TP Configuration List window  
opens.  
5. Select an LNS entry from the list.  
6. Set the Domain Name Delimiter  
parameter. Click on Help or see the  
parameter description on page A-7.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
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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 information about tunnel authentication, see “Tunnel Authentication” on  
page 1-12.  
To enable tunnel authentication, complete the following tasks:  
Site Manager Procedure  
You do this  
System responds  
1. In the Configuration Manager window,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose Tunnel Authentication.  
The L2TP Tunnel Security List window  
opens.  
5. Select an LNS entry from the list.  
6. Set the following parameters:  
Enable Tunnel Authentication  
Tunnel Authentication Password  
Click on Help or see the parameter  
descriptions on page A-9.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
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Customizing L2TP Services  
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 sites.  
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  
1. In the Configuration Manager window,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP IP Interface.  
5. Select an LNS entry from the list.  
6. Click on Change.  
The L2TP IP Interface List window opens.  
The L2TP IP Interface window opens.  
7. Modify the following parameters:  
L2TP IP Interface Address  
Subnet Mask  
Click on Help or see the parameter  
descriptions beginning on page A-11.  
8. Click on OK.  
You return to the L2TP IP Interface List  
window. The new address appears in the  
list.  
9. Click on Done.  
You return to the Configuration Manager  
window.  
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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:  
Site Manager Procedure  
You do this  
System responds  
1. In the Configuration Manager window,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP IP Interface.  
5. Select an LNS entry from the list.  
The L2TP IP Interface List window opens.  
6. Set the RIP Enable parameter to Disable.  
Click on Help or see the parameter  
description on page A-12.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
Disabling L2TP  
To disable L2TP on a slot, complete the following tasks:  
Site Manager Procedure  
You do this  
System responds  
1. In the Configuration Manager window,  
The Protocols menu opens.  
choose Protocols.  
2. Choose IP.  
The IP menu opens.  
3. Choose L2TP.  
The L2TP menu opens.  
4. Choose L2TP Configuration.  
The L2TP Configuration List window  
opens.  
5. Select an LNS entry from the list.  
(continued)  
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Customizing L2TP Services  
Site Manager Procedure (continued)  
You do this  
System responds  
6. Set the Enable L2TP parameter to  
Disable. Click on Help or see the  
parameter description on page A-3.  
Site Manager disables L2TP for the slot.  
7. Click on Done.  
You return to the Configuration Manager  
window.  
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.  
The Edit Connector window opens.  
2. Choose Edit Circuit.  
3. Choose Protocols.  
4. Choose Add/Delete.  
5. Click on L2TP.  
The Circuit Definition window opens.  
The Protocols menu opens.  
The Select Protocols window opens.  
Site Manager deselects L2TP.  
6. Click on OK.  
You return to the Circuit Definition  
window.  
7. Choose File.  
The File menu opens.  
8. Choose Exit.  
You return to the Configuration Manager  
window.  
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Configuring L2TP Services  
Deleting L2TP from a Frame Relay Interface  
To delete L2TP from a frame relay 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.  
The Edit Connector window opens.  
2. Choose Edit Circuit.  
The Frame Relay Circuit Definition  
window opens.  
3. Choose Services.  
The Frame Relay Service List window  
opens.  
4. Choose Protocols in the top left corner of The Protocols menu opens.  
the window.  
5. Choose Add/Delete.  
6. Click on L2TP.  
7. Click on OK.  
The Select Protocols window opens.  
Site Manager deselects L2TP.  
You return to the Frame Relay Service  
List window.  
8. Click on Done.  
You return to the Frame Relay Circuit  
Definition window.  
9. Click on Done.  
You return to the Configuration Manager  
window.  
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Customizing L2TP Services  
Deleting L2TP from an ATM Interface  
To delete L2TP from an ATM interface on a COM connector, complete the  
following tasks:  
Site Manager Procedure  
System responds  
You do this  
1. In the Configuration Manager window,  
click on a COM connector configured with  
L2TP.  
The Edit Connector window opens.  
2. Choose Edit Circuit.  
3. Choose Group Protocols.  
4. Choose Add/Delete.  
5. Click on L2TP.  
The Circuit Definition window opens.  
The Group Protocols menu opens.  
The Select Protocols window opens.  
Site Manager deselects L2TP.  
6. Click on OK.  
You return to the Circuit Definition  
window.  
7. Choose File.  
The File menu opens.  
8. Choose Exit.  
You return to the Configuration Manager  
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.  
The Edit ATM Connector window opens.  
2. Choose Service Attributes.  
The ATM Service Records List window  
opens.  
3. Choose Protocols in the top left corner of The Protocols menu opens.  
the window.  
4. Choose Add/Delete.  
The Select Protocols window opens.  
Site Manager deselects L2TP.  
5. Click on L2TP.  
(continued)  
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Configuring L2TP Services  
Site Manager Procedure (continued)  
You do this  
System responds  
6. Click on OK.  
You return to the ATM Service Records  
List window.  
7. Click on Done.  
You return to the Edit ATM Connector  
window.  
8. Click on Done.  
You return to the Configuration Manager  
window.  
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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  
Topic  
Page  
L2TP Configuration Parameters  
L2TP Tunnel Security Parameters  
L2TP IP Interface Parameters  
A-2  
A-8  
A-10  
For each parameter, this appendix provides 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  
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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.  
Figure A-1.  
L2TP Configuration List Window  
The parameter descriptions follow.  
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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 automatically sets this parameter to Enable when you select 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 sessions that you want the LNS to support.  
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  
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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 activity  
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  
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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 acknowledgment to the LAC that it received an L2TP control message,  
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  
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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: Identifies the 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 | Disable  
Function: Specifies whether the LNS uses flow control on the tunneled data packets. Flow  
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  
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L2TP Parameters  
Parameter: Remove Domain Name  
Path: Configuration Manager > Protocols > IP > L2TP > L2TP Configuration  
Default: Enable  
Options: Enable | Disable  
Function: Instructs the router whether to remove the domain name from the 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 identify the user without having to reconfigure 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  
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Configuring L2TP Services  
L2TP Tunnel Security Parameters  
The L2TP Tunnel Security List window (Figure A-2) contains the tunnel  
authentication parameters.  
Figure A-2.  
L2TP Tunnel Security List Window  
The parameter descriptions follow.  
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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 the LNS to the LAC if the devices are using tunnel authentication. 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  
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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.  
Figure A-3.  
L2TP IP Interface List Window  
When you click on Change, Site Manager displays the L2TP IP Interface window  
(Figure A-4).  
Figure A-4.  
L2TP IP Interface Window  
A-10  
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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  
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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  
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Appendix B  
Configuration Examples  
This appendix provides two examples of L2TP network configurations. 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 that you are familiar 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 network. In this network, 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 connection between the ISP network  
and the corporate network.  
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Configuring L2TP Services  
No active call from mmark;  
no tunnel needed  
ISP network  
LAC 2  
PC  
TMS  
No L2TP  
functionality  
Modem  
Corporate  
network  
Router  
LNS  
192.32.16.55  
LAC 1  
Frame relay  
Tunnel  
.26.0  
.17  
PC  
TA  
Multilink  
PPP  
192.32.68.2  
L2TP IP  
interface  
No L2TP  
ISDN  
RADIUS server  
192.32.26.6  
bay_private  
functionality  
Domain name in TMS database  
baynetworks.com = 192.32.16.55  
IP addresses in the  
RADIUS server database  
192.32.40.1 [email protected]  
192.32.40.2 [email protected]  
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 internal 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 are [email protected] and  
B-2  
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Configuration Examples  
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 documentation 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.  
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 Address  
RADIUS Primary Server Password  
RADIUS Client IP Address  
192.32.26.6  
bay_private  
192.32.16.55  
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Configuring L2TP Services  
6. In the L2TP Tunneling Security window, enable tunnel authentication.  
Parameter Name  
Value  
Enable Tunnel Authentication  
Tunnel Authentication Password  
Enable  
LAC1  
7. In the L2TP IP Interface window, enter the L2TP IP address.  
Parameter Name  
Value  
L2TP IP Interface Address  
Subnet Mask  
192.32.68.2  
255.255.255.0  
During the L2TP session, the RADIUS server assigns the following IP  
addresses:  
[email protected]: 192.32.40.1  
[email protected]: 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  
verifies the domain name and address and sends this information 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 [email protected] 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  
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Configuration Examples  
Example 2: Remote Router Calling the Corporate Network  
Figure B-2 shows a network with 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 for the connection between the ISP network 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:  
[email protected]: 192.32.40.1  
[email protected]: 192.32.40.2  
No active call from mmark;  
no tunnel needed  
ISP network  
LAC 2  
mmark@bay.com  
TMS  
PC  
PC  
No L2TP  
Corporate  
network  
Modem  
functionality  
Router  
LNS  
192.32.16.55  
LAC 1  
jsmart@bay.com  
PPP  
Tunnel  
.26.0  
.17  
TA  
ISDN  
No L2TP  
functionality  
Multilink  
PPP  
192.32.40.254  
L2TP IP  
interface  
RADIUS server  
192.32.26.6  
bay_private  
Domain name in TMS database  
bay.com = 192.32.16.55  
IP addresses in the  
RADIUS server database  
192.32.40.1 jsmart@bay.com  
192.32.40.2 mmark@bay.com  
L2T0008B  
Figure B-2.  
L2TP Network with Routers at the Remote Site  
The LNS configuration in this example is the same as in Example 1; however, you  
must modify the configuration of the remote AN router. Go to the next sections.  
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Configuring L2TP Services  
Configuring the Dial-on-Demand Circuit  
Modify the dial-on-demand circuit configuration for the AN routers as follows:  
1. In the Configuration 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  
CHAP Local Name  
Disable  
jsmart@bay.com  
Enabled  
Dial Optimized Routing  
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 information 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 information about PPP, see Configuring PPP Services.  
B-6  
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Appendix C  
Troubleshooting  
To monitor your L2TP network and solve problems that may occur, first check the  
event log file for any messages recorded by the LNS. For information about  
viewing and reading event messages, see Event Messages for Routers and  
Configuring and Managing Routers with Site Manager.  
Table C-1 provides troubleshooting solutions for common problems with your  
L2TP network.  
Table C-1.  
Problem  
Common L2TP Network Problems and Solutions  
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 password is the same for the LAC 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)  
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Configuring L2TP Services  
(continued)  
Table C-1.  
Problem  
Common L2TP Network Problems and Solutions  
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  
set the PPP parameter RFC1661 Compliance to  
Enable.  
You can also check the session statistics, which are  
automatically enabled on the LNS.  
Bay Networks router at the remote Check the IP address assigned by the RADIUS  
site cannot tunnel into the  
corporate network.  
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.  
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.  
C-2  
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Index  
A
L
Ack Timeout (milliseconds) parameter, A-5  
acronyms, xv  
L2TP  
B
C
purpose, 1-2  
configuration examples, B-1  
troubleshooting, C-1  
D
deleting L2TP  
from ATM, 3-13  
from frame relay, 3-12  
from PPP, 3-11  
L2TP network server. See LNS  
LAC  
E
LNS  
changing system name, 3-4  
configuration example, B-3  
configuring router as, 2-3  
customizing parameters, 3-1  
description, 1-6  
Enable L2TP parameter, A-3  
Enable Tunnel Authentication parameter, A-9  
H
Hello Timer (seconds) parameter, A-4  
enabling tunnel authentication, 3-8  
303532-A Rev 00  
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LNS (continued)  
S
L2TP security, 1-10  
modifying protocol configuration, 3-2  
sessions, L2TP  
description, 1-3  
LNS system name, changing, 3-4  
M
T
Max L2TP Sessions parameter, A-3  
technical publications, xvi  
technical support, xvi  
P
text conventions, xiv  
TMS, description, 1-5, 1-12  
troubleshooting network problems, C-1  
parameters  
tunnel authentication  
enabling, 3-8  
customizing, 3-1  
Tunnel Authentication Password parameter, A-9  
tunnel management server. See TMS  
tunnel, description, 1-2  
setting, 3-3  
password, tunnel authentication  
description, 1-12  
setting, 3-8  
U
user authentication, RADIUS, 1-14  
V
R
virtual private network (VPN), description, 1-1  
changing address and password, 3-3  
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  
Index-2  
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