Configuring NAS-Initiated Dial-In VPDN Tunneling

Network access server (NAS)-initiated dial-in tunneling provides secure tunneling of a PPP session from a NAS to a tunnel server without any special knowledge or interaction required from the client.

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Prerequisites for Configuring NAS-Initiated Dial-In VPDN Tunneling

  • Before performing the tasks documented in this module, you must perform the required tasks in the Configuring AAA for VPDNs module.

  • The NAS should be configured to receive incoming calls from clients using ISDN, the Public Switched Telephone Network (PSTN), Digital Subscriber Line (DSL), or cable modem .

Restrictions for Configuring NAS-Initiated Dial-In VPDN Tunneling

  • Layer 2 Forwarding (L2F) protocol is not supported on the Cisco ASR 1000 Series Aggregation Services Routers.

Information About NAS-Initiated Dial-In VPDN Tunneling

NAS-Initiated Dial-in VPDN Tunneling

NAS-initiated dial-in VPDN tunneling is also known as compulsory tunneling. In NAS-initiated dial-in VPDN tunneling, the client dials in to the NAS through a medium that supports PPP. If the connection from the client to the Internet service provider (ISP) NAS is over a medium that is considered secure, such as DSL, ISDN, or the PSTN, the client might choose not to provide additional security. The PPP session is securely tunneled from the NAS to the tunnel server without any special knowledge or interaction required from the client. NAS-initiated dial-in VPDN tunnels can use either the Layer 2 Tunneling Protocol (L2TP) or the Layer 2 Forwarding (L2F) protocol.


Note

The Cisco ASR 1000 Series Aggregation Services Routers support only L2TP.

A NAS-initiated dial-in tunneling scenario is shown in the figure below.

Figure 1. NAS-Initiated Dial-In VPDN Scenario

L2TP Calling Station ID Suppression

In a NAS-initiated dial-in L2TP tunneling scenario, when the NAS connects to a tunnel server it transfers numerous attribute-value (AV) pairs as part of the session setup process. One of these AV pairs is L2TP AV pair 22, the Calling Number ID. The Calling Number ID AV pair includes the calling station ID of the originator of the session, which can be the phone number of the originator, the Logical Line ID (LLID) used to make the connection on the LAC, or the MAC address of the PC connecting to the network. This information can be considered sensitive in cases where the NAS and tunnel server are being managed by different entities. Depending on the security requirements of the NAS or end users, it might be desirable for the NAS to suppress part or all of the calling station ID.

Parts of the calling station ID can be masked, or the calling station ID can be removed completely. Calling station ID suppression can be configured globally on the NAS, for individual VPDN groups on the NAS, or on the remote RADIUS server if one is configured.

L2TP Failover

If a NAS fails to contact its peer during L2TP tunnel establishment, it can fail over to another configured tunnel server and attempt tunnel establishment with that device.

Failover can occur in these scenarios:

  • If the router sends a Start Control Connection Request (SCCRQ) a number of times and receives no response from the peer

  • If the router receives a Stop Control Connection Notification (StopCCN) from its peer

  • If the router receives a Call Disconnect Notify (CDN) message from its peer

In both the StopCCN control message and the CDN control message, a Result Code AV pair is included, which indicates the reason for tunnel or session termination, respectively. This AV pair might also include an optional Error Code, which further describes the nature of the termination. The various Result Code and Error Code values have been standardized in RFC 2661. Failover will occur if the combination of Result Code and Error Code values as defined in the table below is received from the peer.

Table 1. Defined Result and Error Codes from RFC 2661

Control Message

Result Code

Error Code

StopCCN, CDN

2: General error, see Error Code.

4: Insufficient resources to handle this operation now.

6: A generic vendor-specific error occurred.1

7: Try another.

9: Try another directed.

CDN

4: Temporary lack of resources.

--

1 For failover, this error code would be accompanied by a vendor-specific error AVP in the error message--in this case containing the Cisco vendor code (SMI_CISCO_ENTERPRISE_CODE) and a Cisco error code (L2TP_VENDOR_ERROR_SLIMIT).

When one of the three scenarios occurs, the router marks the peer IP address as busy for 60 seconds by default. During that time no attempt is made to establish a session or tunnel with the peer. The router selects an alternate peer to contact if one is configured. If a tunnel already exists to the alternate peer, new sessions are brought up in the existing tunnel. Otherwise, the router begins negotiations to establish a tunnel to the alternate peer.

How to Configure NAS-Initiated Dial-In VPDN Tunneling

Configuring the NAS to Request Dial-In VPDN Tunnels

The NAS must be configured to request tunnel establishment with the remote tunnel server. Perform this task on the NAS to configure a VPDN request dial-in subgroup and the IP address of the tunnel server that will be the other endpoint of the VPDN tunnel.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. vpdn-group name
  4. description string
  5. request-dialin
  6. protocol l2tp
  7. Do one of the following:
    • domain domain-name
    • dnis {dnis-number | dnis-group-name }
  8. exit
  9. initiate-to ip ip-address [limit limit-number ] [priority priority-number ]

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

vpdn-group name

Example:


Router(config)# vpdn-group 1

Creates a VPDN group and enters VPDN group configuration mode.

Step 4

description string

Example:


Router(config-vpdn)# description myvpdngroup

(Optional) Adds a description to a VPDN group.

Step 5

request-dialin

Example:


Router(config-vpdn)# request-dialin

Configures a NAS to request the establishment of an L2F or L2TP tunnel to a tunnel server, creates a request-dialin VPDN subgroup, and enters VPDN request dial-in subgroup configuration mode.

Step 6

protocol l2tp

Example:


Router(config-vpdn-req-in)# protocol l2tp

Specifies the Layer 2 protocol that the VPDN group will use.

Step 7

Do one of the following:

  • domain domain-name
  • dnis {dnis-number | dnis-group-name }

Example:


Router(config-vpdn-req-in)# domain example.com

Example:


Router(config-vpdn-req-in)# dnis 5687

Requests that PPP calls from a specific domain name be tunneled.

or

Requests that PPP calls from a specific Dialed Number Identification Service (DNIS) number or DNIS group be tunneled.

Step 8

exit

Example:


Router(config-vpdn-req-in)# exit

Exits to VPDN group configuration mode.

Step 9

initiate-to ip ip-address [limit limit-number ] [priority priority-number ]

Example:


Router(config-vpdn)# initiate-to ip 10.1.1.1 limit 12

Specifies an IP address that will be used for Layer 2 tunneling.

  • limit --Maximum number of connections that can be made to this IP address.

  • priority --Priority for this IP address.

Note 

The priority keyword is typically not configured on a NAS. Information used for load balancing and failover is configured on a remote authentication, authorization, and accounting (AAA) server instead. See the Configuring AAA for VPDNs module.

  • Multiple tunnel servers can be configured on the NAS by configuring multiple initiate-to commands.

What to Do Next

You must perform the task in the Configuring the Tunnel Server to Accept Dial-In VPDN Tunnels section.

Configuring the Tunnel Server to Accept Dial-In VPDN Tunnels

The tunnel server must be configured to accept tunnel requests from the remote NAS. Perform this task on the tunnel server to create a VPDN accept dial-in subgroup and to configure the tunnel server to accept tunnels from the NAS that will be the other endpoint of the VPDN tunnel. To configure the tunnel server to accept tunnels from multiple NASs, you must perform this task for each NAS.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. vpdn-group name
  4. description string
  5. accept-dialin
  6. protocol l2tp
  7. virtual-template number
  8. exit
  9. terminate-from hostname host-name
  10. lcp renegotiation {always | on-mismatch }
  11. force-local-chap

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

vpdn-group name

Example:


Router(config)# vpdn-group 1

Creates a VPDN group and enters VPDN group configuration mode.

Step 4

description string

Example:


Router(config-vpdn)# description myvpdngroup

(Optional) Adds a description to a VPDN group.

Step 5

accept-dialin

Example:


Router(config-vpdn)# accept-dialin

Configures a tunnel server to accept requests from a NAS to establish an L2F or L2TP tunnel, creates an accept-dialin VPDN subgroup, and enters VPDN accept dial-in subgroup configuration mode.

Step 6

protocol l2tp

Example:


Router(config-vpdn-acc-in)# protocol l2tp

Specifies the Layer 2 protocol that the VPDN group will use.

Step 7

virtual-template number

Example:


Router(config-vpdn-acc-in)# virtual-template 1

Specifies which virtual template will be used to clone virtual access interfaces.

Step 8

exit

Example:


Router(config-vpdn-acc-in)# exit

Exits to VPDN group configuration mode.

Step 9

terminate-from hostname host-name

Example:


Router(config-vpdn)# terminate-from hostname NAS12

Specifies the hostname of the remote NAS that will be required when accepting a VPDN tunnel.

Step 10

lcp renegotiation {always | on-mismatch }

Example:


Router(config-vpdn)# lcp renegotiation always

(Optional) Allows the tunnel server to renegotiate the PPP Link Control Protocol (LCP) on dial-in calls using L2TP or L2F.

  • This command is useful for a tunnel server that tunnels to a non-Cisco NAS, where the NAS might negotiate a different set of LCP options than what the tunnel server expects.

Step 11

force-local-chap

Example:


Router(config-vpdn)# force-local-chap

(Optional) Forces the tunnel server to reauthenticate the client.

  • Enabling this command forces the tunnel server to reauthenticate the client in addition to the proxy authentication that occurs at the NAS.

Note 

This command will function only if Challenge Handshake Authentication Protocol (CHAP) authentication is enabled for PPP using the ppp authentication chap command in the virtual template configured on the tunnel server.

What to Do Next

You must perform the task in the Configuring the Virtual Template on the Tunnel Server section.

Configuring the Virtual Template on the Tunnel Server

When a request to establish a tunnel is received by the tunnel server, the tunnel server must create a virtual access interface. The virtual access interface is cloned from a virtual template interface, used, and then freed when no longer needed. The virtual template interface is a logical entity that is not tied to any physical interface.

Perform this task on the tunnel server to configure a basic virtual template .

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface virtual-template number
  4. ip unnumbered type number
  5. ppp authentication protocol1 [protocol2 ...] [if-needed ] [list-name | default ] [callin ] [one-time ] [optional ]
  6. peer default ip address {ip-address | dhcp-pool | dhcp | pool [pool-name ]}
  7. encapsulation encapsulation-type

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

interface virtual-template number

Example:


Router(config)# interface virtual-template 1

Enters interface configuration mode and creates a virtual template interface that can be configured and applied dynamically in creating virtual access interfaces.

Step 4

ip unnumbered type number

Example:


Router(config-if)# ip unnumbered FastEthernet 0/0

Enables IP processing on a serial interface without assigning an explicit IP address to the interface.

Note 

Configuring the ip address command within a virtual template is not recommended. Configuring a specific IP address in a virtual template can result in the establishment of erroneous routes and the loss of IP packets.

Step 5

ppp authentication protocol1 [protocol2 ...] [if-needed ] [list-name | default ] [callin ] [one-time ] [optional ]

Example:


Router(config-if)# ppp authentication chap

Enables at least one PPP authentication protocol and specifies the order in which the protocols are selected on the interface.

Step 6

peer default ip address {ip-address | dhcp-pool | dhcp | pool [pool-name ]}

Example:


Router(config-if)# peer default ip address pool mypool

Specifies an IP address, an address from a specific IP address pool, or an address from the Dynamic Host Configuration Protocol (DHCP) mechanism to be returned to a remote peer connecting to this interface.

Step 7

encapsulation encapsulation-type

Example:


Router(config-if)# encapsulation ppp

Sets the encapsulation method used by the interface.

Verifying a NAS-Initiated VPDN Configuration

Verifying and Troubleshooting Tunnel Establishment Between the NAS and the Tunnel Server

Perform this task to verify that a tunnel between the NAS and the tunnel server has been established, and to troubleshoot problems with tunnel establishment.

SUMMARY STEPS

  1. enable
  2. show vpdn tunnel all
  3. ping ip-address
  4. debug vpdn event
  5. debug vpdn errors

DETAILED STEPS

Step 1

enable

Enter this command to enable privileged EXEC mode. Enter your password if prompted:

Example:

Router> enable
Step 2

show vpdn tunnel all

Enter this command to display details about all active VPDN tunnels. This example shows an example of No active L2TP tunnels:

Example:

Router# show vpdn tunnel all
% No active L2TP tunnels
.
.
.

If no active tunnels have been established with the NAS, proceed with the following steps to troubleshoot the problem.

Step 3

ping ip-address

Enter this command to ping the NAS. The following output shows the result of a successful ping from the tunnel server to the NAS:

Example:

Router# ping 172.22.66.25
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.30.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 128/132/152 ms

If the tunnel server is unable to ping the NAS, there might be a problem with the routing path between the devices, or the NAS might not be functional.

Step 4

debug vpdn event

Enter this command to display the VPDN events that occur during tunnel establishment. The following output from the tunnel server shows normal VPDN tunnel establishment for an L2TP tunnel:

Example:

Router# debug vpdn event
20:19:17: L2TP: I SCCRQ from ts1 tnl 8
20:19:17: L2X: Never heard of ts1
20:19:17: Tnl 7 L2TP: New tunnel created for remote ts1, address 172.21.9.4
20:19:17: Tnl 7 L2TP: Got a challenge in SCCRQ, ts1
20:19:17: Tnl 7 L2TP: Tunnel state change from idle to wait-ctl-reply
20:19:17: Tnl 7 L2TP: Got a Challenge Response in SCCCN from ts1
20:19:17: Tnl 7 L2TP: Tunnel Authentication success
20:19:17: Tnl 7 L2TP: Tunnel state change from wait-ctl-reply to established
20:19:17: Tnl 7 L2TP: SM State established
20:19:17: Tnl/Cl 7/1 L2TP: Session FS enabled
20:19:17: Tnl/Cl 7/1 L2TP: Session state change from idle to wait-for-tunnel
20:19:17: Tnl/Cl 7/1 L2TP: New session created
20:19:17: Tnl/Cl 7/1 L2TP: O ICRP to ts1 8/1
20:19:17: Tnl/Cl 7/1 L2TP: Session state change from wait-for-tunnel to wait-connect
20:19:17: Tnl/Cl 7/1 L2TP: Session state change from wait-connect to established
20:19:17: Vi1 VPDN: Virtual interface created for user1@cisco.com
20:19:17: Vi1 VPDN: Set to Async interface
20:19:17: Vi1 VPDN: Clone from Vtemplate 1 filterPPP=0 blocking
20:19:18: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to up
20:19:18: Vi1 VPDN: Bind interface direction=2
20:19:18: Vi1 VPDN: PPP LCP accepting rcv CONFACK
20:19:19: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access1, changed state to up
Step 5

debug vpdn errors

Enter this command to display error messages that are generated during tunnel establishment. The following output from the NAS shows an authentication failure during tunnel establishment.

Example:

Router# debug vpdn errors
%LINEPROTO-5-UPDOWN: Line protocol on Interface Async1, changed state to down
%LINK-5-CHANGED: Interface Async1, changed state to reset
%LINK-3-UPDOWN: Interface Async1, changed state to down
%LINK-3-UPDOWN: Interface Async1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Async1, changed state to up
VPDN tunnel management packet failed to authenticate
VPDN tunnel management packet failed to authenticate

If an authentication failure occurs, verify that both the NAS and the tunnel server are configured with the same secret password. You can also perform tasks to verify L2TP tunnel establishment, PPP negotiations, and authentication with the remote client as described in the Configuring AAA for VPDNs module.

Verifying the Connection Between the Client and the NAS

Perform this task to verify the connection between the dial-in client and the NAS.

SUMMARY STEPS

  1. Dial in to the NAS from a client PC.
  2. enable
  3. show caller user user
  4. show interfaces virtual-access number
  5. show vpdn session

DETAILED STEPS

Step 1

Dial in to the NAS from a client PC.

Ensure that the client PC is able to connect to the NAS by establishing a dial-in connection. As the call comes into the NAS, a LINK-3-UPDOWN message automatically appears on the NAS terminal screen. In the following example, the call comes into the NAS on asynchronous interface 14:

Example:

*Jan  1 21:22:18.410: %LINK-3-UPDOWN: Interface Async14, changed state to up
Note 

No debug commands are turned on to display this log message. This message should be displayed within 30 seconds after the client first sends the call.

If this message is not displayed by the NAS, there is a problem with the dial-in configuration.
Step 2

enable

Enter this command to enable privileged EXEC mode. Enter your password if prompted:

Example:

Router> enable
Step 3

show caller user user

Enter this command on the tunnel server to verify that the client received an IP address. The following example shows that user3 is using IP address 10.0.0.1.

Example:

Router# show caller user user3@cisco.com
User: user3@cisco.com, line Vi2.502, service PPPoVPDN 
Connected for 1d10h 
Timeouts: Limit Remaining Timer Type 
- - - 
PPP: LCP Open, CHAP (<-), IPCP 
IP: Local 10.0.0.1, remote 172.16.2.247 
Counts: 2052 packets input, 32826 bytes 
        2053 packets output, 106742 bytes

If an incorrect IP address or no IP address is displayed, there is a problem with IP addresses assignment. Verify the configuration of the peer default ip address command in the virtual template on the tunnel server.

Step 4

show interfaces virtual-access number

Enter this command to verify that the interface is up, that LCP is open, and that no errors are reported. The following output shows a functional interface:

Example:

Router# show interfaces virtual-access 2.502
Virtual-Access2.502 is up, line protocol is up
  Hardware is Virtual Access interface
  Interface is unnumbered. Using address of Loopback1001 (60.0.0.1)
  MTU 1454 bytes, BW 2000000 Kbit, DLY 100000 usec,
     reliability 255/255, txload 1/255, rxload 5/255
  Encapsulation PPP, LCP Open
  Open: IPCP
  PPPoVPDN vaccess, cloned from Virtual-Template1
  Vaccess status 0x0
  Protocol l2tp, tunnel id 30485, session id 55909
  Keepalive set (60 sec)
     2056 packets input, 32890 bytes
     2057 packets output, 106950 bytes
  Last clearing of ''show interface'' counters never

The virtual access interface is up and the line protocol is up, showing that virtual interface establishment was successful.

Step 5

show vpdn session

Enter this command on the tunnel server to verify that there are active VPDN sessions. This example shows output from a tunnel server with several active tunnels.

Example:

Router# show vpdn session
L2TP Session Information Total tunnels 4000 sessions 15960
LocID      RemID      TunID      Username, Intf/      State  Last Chg Uniq ID
                                 Vcid, Circuit
43202      40336      22         user@ci..., Vi2.9171 est    1d10h 9184
34090      31996      22         user@ci..., Vi2.1734 est    1d10h 1735
1217       42591      22         user@ci..., Vi2.9312 est    1d10h 9325
6737       22325      22         user@ci..., Vi2.1729 est    1d10h 1730
59420      17035      34         user@ci..., Vi2.9338 est    1d10h 9351
45069      60982      34         user@ci..., Vi2.1645 est    1d10h 1646
27825      44751      34         user@ci..., Vi2.1653 est    1d10h 1654
24600      7627       34         user@ci..., Vi2.9096 est    1d10h 9109
13018      65037      43         user@ci..., Vi2.8166 est    1d10h 8179
43090      34448      43         user@ci..., Vi2.8176 est    1d10h 8189
31798      41505      43         user@c..., Vi2.15752 est    1d10h 15765
56832      64322      43         user@c..., Vi2.15655 est    1d10h 15668
53944      25409      48         user@c..., Vi2.14115 est    1d10h 14128
16215      52915      48         user@c..., Vi2.14134 est    1d10h 14147
17332      14000      48         user@ci..., Vi2.6630 est    1d10h 6643
12466      54817      48         user@ci..., Vi2.6622 est    1d10h 6635
28290      37822      50         user@ci..., Vi2.5094 est    1d10h 15905
44839      30137      50         user@c..., Vi2.15875 est    1d10h 15888

If there is no session established for the client, perform the troubleshooting steps in the Verifying and Troubleshooting Tunnel Establishment Between the NAS and the Tunnel Server.

Configuring L2TP Calling Station ID Suppression

Calling station ID suppression can be configured globally on the NAS, for individual VPDN groups on the NAS, or on the remote RADIUS server if one is configured.

The order of precedence for L2TP calling station ID suppression configurations is as follows:

  • A RADIUS server configuration will take precedence over any configuration on the NAS.

  • A VPDN group configuration will take precedence over a global configuration for calls associated with that VPDN group.

  • A global configuration will be applied if no other method is configured.

Perform one or more of the following tasks to configure L2TP calling station ID suppression:

Prerequisites for Configuring L2TP Calling Station ID Suppression

  • You must configure the NAS and the tunnel server to use the L2TP protocol when performing the tasks in the Configuring the NAS to Request Dial-In VPDN Tunnels section and the Configuring the Tunnel Server to Accept Dial-In VPDN Tunnels section.

  • You must configure the NAS to tunnel calls based on the domain name when performing the task in the Configuring the NAS to Request Dial-In VPDN Tunnels section.

  • You must configure the VPDN search order to use the domain name when performing the task in the Configuring the VPDN Tunnel Authorization Search Order section of the Configuring AAA for VPDNs module.

Configuring Global L2TP Calling Station ID Suppression on the NAS

The calling station ID information included in L2TP AV pair 22 can be removed or masked for every L2TP session established on the router if you configure L2TP calling station ID suppression globally. This configuration is compatible with either local or remote authorization.

Perform this task on the NAS to configure global L2TP calling station ID suppression.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. vpdn l2tp attribute clid mask-method {right mask-character characters | remove } [match match-string ]

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

vpdn l2tp attribute clid mask-method {right mask-character characters | remove } [match match-string ]

Example:

Router(config)# vpdn l2tp attribute clid mask-method right # 6 match %321

Configures a NAS to suppress L2TP calling station IDs globally on the router.

  • right mask-character characters --Masks the calling station ID starting from the right end, using the specified mask-character to replace the defined number of characters . The mask-character must be a printable character.

  • remove --Removes the entire calling station ID.

  • match match-string --Removes or masks the calling station ID only when the username contains the specified match-string .

Configuring L2TP Calling Station ID Suppression for a VPDN Group on the NAS

The calling station ID information included in L2TP AV pair 22 can be removed or masked for calls associated with a specific VPDN group. This configuration is compatible with local authorization configurations.

Perform this task on the NAS to configure L2TP calling station ID suppression for calls associated with a particular VPDN group when using local authorization.

Before you begin

  • You must configure the NAS and the tunnel server for local authorization when performing the task in the Configuring AAA on the NAS and the Tunnel Server section of the Configuring AAA for VPDNs module.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. vpdn-group name
  4. l2tp attribute clid mask-method {right mask-character characters | remove } [match match-string ]

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

vpdn-group name

Example:

Router(config)# vpdn-group L2TP

Creates a VPDN group and enters VPDN group configuration mode.

Step 4

l2tp attribute clid mask-method {right mask-character characters | remove } [match match-string ]

Example:

Router (config-vpdn)# l2tp attribute clid mask-method remove

Configures a NAS to suppress L2TP calling station IDs for sessions associated with a VPDN group or VPDN template.

  • right mask-character characters --Masks the calling station ID starting from the right end, using the specified mask-character to replace the defined number of characters . The mask-character must be a printable character.

  • remove --Removes the entire calling station ID.

  • match match-string --Removes or masks the calling station ID only when the username contains the specified match-string .

Configuring L2TP Calling Station ID Suppression on the NAS Remote RADIUS Server

L2TP calling station ID suppression can be configured directly on the NAS, or in the RADIUS user profile. Configuring L2TP calling station ID suppression in the RADIUS user profile allows the configuration to be propagated to multiple NASs without having to configure each one.

Perform this task on the RADIUS server to configure a user profile that will allow the RADIUS server to instruct NASs to remove or mask the L2TP calling station ID.

Before you begin

  • The NAS must be configured for remote RADIUS AAA. Perform the tasks for configuring AAA on the NAS and the tunnel server, and configuring remote AAA for VPDNs as described in the Configuring AAA for VPDNs module.

  • The RADIUS server must be configured for AAA.

SUMMARY STEPS

  1. Cisco-Avpair = vpdn:l2tp-tunnel-password= secret
  2. Cisco-Avpair = vpdn:tunnel-type= l2tp
  3. Cisco-Avpair = vpdn:tunnel-id= name
  4. Cisco-Avpair = vpdn:ip-address= address
  5. Cisco-Avpair = vpdn:l2tp-clid-mask-method= {right: character : characters | remove }

DETAILED STEPS

  Command or Action Purpose
Step 1

Cisco-Avpair = vpdn:l2tp-tunnel-password= secret

Example:

Cisco-Avpair = vpdn:l2tp-tunnel-password=cisco

Specifies the L2TP tunnel password in the RADIUS user profile.

Step 2

Cisco-Avpair = vpdn:tunnel-type= l2tp

Example:

Cisco-Avpair = vpdn:tunnel-type=l2tp

Specifies L2TP as the tunneling protocol in the RADIUS user profile.

Step 3

Cisco-Avpair = vpdn:tunnel-id= name

Example:

Cisco-Avpair = vpdn:tunnel-id=test

Specifies the tunnel ID in the RADIUS user profile.

Step 4

Cisco-Avpair = vpdn:ip-address= address

Example:

Cisco-Avpair = vpdn:ip-address=172.16.9.9

Specifies the NAS IP address in the RADIUS user profile.

Step 5

Cisco-Avpair = vpdn:l2tp-clid-mask-method= {right: character : characters | remove }

Example:

Cisco-Avpair = vpdn:l2tp-clid-mask-method= right:#:5

Specifies L2TP calling station ID suppression parameters in the RADIUS user profile.

  • right --Masks the calling station ID starting from the right side, using the specified mask-character to replace the defined number of characters .

  • remove --Removes the entire calling station ID.

Configuration Examples for NAS-Initiated Dial-In VPDN Tunneling

Example Configuring the NAS for Dial-In VPDNs

The following example configures a NAS named ISP-NAS to tunnel PPP calls to a tunnel server named ENT-TS using L2TP and local authentication and authorization: 


! Enable AAA authentication and authorization with RADIUS as the default method
aaa new-model
aaa authentication ppp default radius
aaa authorization network default radius
!
! Configure the VPDN tunnel authentication password using the local name
username ISP-NAS password 7 tunnelme
username ENT-TS password 7 tunnelme
!
vpdn enable
!
! Configure VPN to first search on the client domain name and then on the DNIS 
vpdn search-order domain dnis
!
! Allow a maximum of 10 simultaneous VPDN sessions
vpdn session-limit 10
!
! Configure the NAS to initiate VPDN dial-in sessions to the tunnel server
vpdn-group 1
 request-dialin
 protocol l2tp
 domain cisco.com
!
 initiate-to ip 172.22.66.25 
 local name ISP-NAS
!
! Specifies the RADIUS server IP address, authorization port, and accounting port
radius-server host 172.22.66.16 auth-port 1645 acct-port 1646
!
! Specifies the authentication key to be used with the RADIUS server
radius-server key cisco
!

Example Configuring the Tunnel Server for Dial-in VPDNs

The following example show a tunnel server named ENT-TS configured to accept L2TP tunnels from a NAS named ISP-NAS using local authentication and authorization: 


! Configure AAA to first use the local database and then contact the RADIUS server for
! PPP authentication
aaa new-model
aaa authentication ppp default local radius
!
! Configure AAA network authorization and accounting by using the RADIUS server
aaa authorization network default radius
aaa accounting network default start-stop radius
!
! Configure the VPDN tunnel authentication password using the local name
username ISP-NAS password 7 tunnelme
username ENT-TS password 7 tunnelme
!
vpdn enable
!
! Configure the tunnel server to accept dial-in sessions from the NAS
vpdn-group 1
 accept-dialin 
 protocol l2tp
 virtual-template 1 
! 
 terminate-from hostname ISP-NAS
 local name ENT-TS
 force-local-chap
!
! Configure the virtual template
interface Virtual-Template1
  gigabitethernet0/0/0
 ppp authentication chap
 peer default ip address pool default
 encapsulation ppp
!
! Specifies the RADIUS server IP address, authorization port, and accounting port
radius-server host 172.22.66.13 auth-port 1645 acct-port 1646
!
! Specifies the authentication key to be used with the RADIUS server
radius-server key cisco

Example L2TP Calling Station ID Suppression with Local Authorization

The following example configures a NAS for PPP over Gigabit Ethernet over virtual LAN (PPPoEoVLAN). The NAS obtains a calling station ID from LLID NAS port preauthorization through RADIUS. The calling station ID will be removed from AV pair 22 for tunnels associated with the VPDN group named L2TP if the string #184 is included in the username. 


hostname LAC
!
enable secret 5 $1$8qtb$MHcYeW2kn8VNYgz932eXl.
enable password lab
!
aaa new-model
!
aaa group server radius LLID-Radius
 server 192.168.1.5 auth-port 1645 acct-port 1646
!
aaa group server radius LAC-Radius
 server 192.168.1.6 auth-port 1645 acct-port 1646
!
aaa authentication ppp default local
aaa authorization network default local 
aaa authorization network LLID group LLID-Radius 
aaa accounting network default start-stop group LAC-Radius
aaa nas port extended
aaa session-id common
!
ip subnet-zero
ip cef
no ip domain lookup
!
vpdn enable
vpdn search-order domain
!
vpdn-group L2TP
 request-dialin
 protocol l2tp
 domain cisco.com
 domain cisco.com#184
!
 initiate-to ip 192.168.1.4 
 local name test
 l2tp tunnel password 0 cisco
 l2tp attribute clid mask-method remove match #184
!
bba-group ppoe 2
 virtual-template 1
 nas-port format d 2/2/4
!
subscriber access pppoe pre-authorize nas-port-id LLID send username
!
interface Loopback0
 no ip address
!
interface Loopback1
 ip address 10.1.1.1 255.255.255.0
!
interface gigabitethernet0/0/0
 ip address 192.168.1.3 255.255.255.0
 no cdp enable
!
interface gigabitethernet0/0/0.20
 encapsulation dot1Q 1024
 no snmp trap link-status
 ppoe enable group 2
 pppoe max-sessions 200
 no cdp enable
!
interface gigabitethernet1/0/0
 ip address 10.1.1.10 255.255.255.0
 no cdp enable
!
interface Serial2/0/0
no ip address
 shutdown
 serial restart-delay 0
!
interface Serial3/0/0
 no ip address
 shutdown
 serial restart-delay 0
!
interface Virtual-Template1
 ip unnumbered gigabitethernet1/0/0 
 ip mroute-cache
 no peer default ip address
 ppp authentication pap
!
ip classless
ip route 0.0.0.0 0.0.0.0 gigabitethernet0/0/0
ip route 10.0.0.0 255.0.0.0 gigabitethernet1/0/0
!
no ip http server
!
radius-server attribute 69 clear
radius-server host 192.168.1.5 auth-port 1645 acct-port 1646
radius-server host 192.168.1.6 auth-port 1645 acct-port 1646
radius-server domain-stripping delimiter #
radius-server key cisco
radius-server vsa send accounting
radius-server vsa send authentication
!
control-plane
!
line con 0
 exec-timeout 0 0
line aux 0
line vty 0 4
 password lab

Example L2TP Calling Station ID Suppression with RADIUS Authorization

The following example configures a NAS for PPPoEoVLAN. The NAS obtains a calling station ID from LLID NAS port preauthorization through RADIUS. The RADIUS user profile specifies that the calling station ID should be masked by replacing the rightmost six characters with the character X.

NAS Configuration


hostname LAC
!
enable secret 5 $1$8qtb$MHcYeW2kn8VNYgz932eXl.
enable password lab
!
aaa new-model
!
aaa group server radius LLID-Radius
 server 192.168.1.5 auth-port 1645 acct-port 1646
!
aaa group server radius LAC-Radius
 server 192.168.1.6 auth-port 1645 acct-port 1646
!
aaa authentication ppp default local
aaa authorization network default group LAC-Radius 
aaa authorization network LLID group LLID-Radius 
aaa accounting network default start-stop group LAC-Radius
aaa nas port extended
aaa session-id common
!
ip subnet-zero
ip cef
no ip domain lookup
!
vpdn enable
vpdn search-order domain
!
bba-group ppoe 2
 virtual-template 1
 nas-port format d 2/2/4
!
subscriber access pppoe pre-authorize nas-port-id LLID send username
!
interface Loopback0
 no ip address
!
interface Loopback1
 ip address 10.1.1.1 255.255.255.0
!
interface gigabitethernet0/0/0
 ip address 192.168.1.3 255.255.255.0
 no cdp enable
!
interface gigabitethernet0/0/0.20
 encapsulation dot1Q 1024
 no snmp trap link-status
 pppoe enable group 2
 pppoe max-sessions 200
 no cdp enable
!
interface gigabitethernet1/0/0
 ip address 10.1.1.10 255.255.255.0
 no cdp enable
!
interface Serial2/0/0
no ip address
 shutdown
 serial restart-delay 0
!
interface Serial3/0/0
 no ip address
 shutdown
 serial restart-delay 0
!
interface Virtual-Template1 
 ip unnumbered gigabitethernet1/0/0
 ip mroute-cache
 no peer default ip address
 ppp authentication pap
!
ip classless
ip route 0.0.0.0 0.0.0.0 gigabitethernet0/0/0
ip route 10.0.0.0 255.0.0.0 gigabitethernet1/0/0
!
no ip http server
!
radius-server attribute 69 clear
radius-server host 192.168.1.5 auth-port 1645 acct-port 1646
radius-server host 192.168.1.6 auth-port 1645 acct-port 1646
radius-server domain-stripping delimiter #
radius-server key cisco
radius-server vsa send accounting
radius-server vsa send authentication
!
control-plane
!
line con 0
 exec-timeout 0 0
line aux 0
line vty 0 4
 password lab

RADIUS User Profile Configuration


Cisco-Avpair = vpdn:l2tp-tunnel-password=cisco
Cisco-Avpair = vpdn:tunnel-type=l2tp
Cisco-Avpair = vpdn:tunnel-id=test
Cisco-Avpair = vpdn:ip-address=192.168.1.4
Cisco-Avpair = vpdn:l2tp-clid-mask-method=right:X:6

Where to Go Next

You can perform any of the relevant optional tasks in the Configuring Additional VPDN Features and in the VPDN Tunnel Management modules.

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

VPDN commands

Cisco IOS VPDN Command Reference

VPDN technology overview

VPDN Technology Overview

Technical support documentation for L2TP

Layer 2 Tunnel Protocol (L2TP)

Technical support documentation for VPDNs

Virtual Private Dial-Up Network (VPDN)

Standards

Standard

Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

--

MIBs

MIB

MIBs Link

  • CISCO-VPDN-MGMT-MIB

  • CISCO-VPDN-MGMT-EXT-MIB

To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

RFCs

RFC

Title

RFC 2661

Layer Two Tunneling Protocol (L2TP)

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for NAS-Initiated Dial-In VPDN Tunneling

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 2. Feature Information for NAS-Initiated Dial-In VPDN Tunneling

Feature Name

Software Releases

Feature Information

L2TP Calling Station ID Suppression

Cisco IOS XE Release 2.1

This feature was introduced on Cisco ASR 1000 Series Aggregation Services Routers.

This feature allows the NAS to suppress part or all of the calling station ID from the NAS in the L2TP AV pair 22, the Calling Number ID. Calling station ID suppression can be configured globally on the router, for individual VPDN groups on the router, or on the remote RADIUS server if one is configured.

The following commands were introduced by this feature: l2tp attribute clid mask-method , vpdn l2tp attribute clid mask-method .

L2TP Extended Failover

Cisco IOS XE Release 2.1

This feature was introduced on Cisco ASR 1000 Series Aggregation Services Routers.

This feature extends L2TP failover to occur if, during tunnel establishment, a router receives a StopCCN message from its peer, or during session establishment a router receives a CDN message from its peer. In either case, the router selects an alternate peer to contact.

No commands were introduced or modified by this feature.