Autosense of ATM PVCs and MUX SNAP Encapsulation

Last Updated: May 22, 2012

The Autosense of MUX/SNAP Encapsulation and PPPoA/PPPoE on ATM PVCs feature enhances PPP over ATM (PPPoA)/PPP over Ethernet (PPPoE) autosense functionality by providing autosense support on multiplexer (MUX) and Subnetwork Access Protocol (SNAP)-encapsulated ATM permanent virtual circuits (PVCs).

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.

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.

Restrictions for Autosense

  • Do not use this feature on a router that initiates PPPoA sessions.
  • This feature supports ATM PVCs. Switched virtual circuits (SVCs) are not supported.
  • PPPoA does not support static IP assignments within virtual templates.

Information About Autosense

PPPoA/PPPoE autosense enables a router to distinguish between incoming PPPoA and PPPoE over ATM sessions and to create virtual access based on demand for both PPP types.

This feature is supported on MUX- and SNAP-encapsulated ATM PVCs and enables the PVC encapsulation type to be autosensed by the router. The router determines the encapsulation type of a PVC by looking at the encapsulation type of the first incoming packet. If the PVC encapsulation type is changed while the PPPoA or PPPoE session on the network access server (NAS) is still up, the incoming packet is dropped, the encapsulation type is reset to autosense, and all sessions are removed from the PVC. The next incoming packet will then determine the new encapsulation type of the PVC.

Benefits of Autosense PPPoA PPPoE for MUX SNAP Encapsulation

The Autosense of PPPoA/PPPoE for MUX or SNAP Encapsulation feature provides resource allocation on demand. For each PVC configured for both PPPoA and PPPoE, certain resources (including one virtual-access interface) are allocated upon configuration, regardless of the existence of a PPPoA or PPPoE session on that PVC. With the Autosense of MUX/SNAP Encapsulation and PPPoA/PPPoE on ATM PVCs feature, resources are allocated for PPPoA and PPPoE sessions only when a client initiates a session, thus reducing overhead on the NAS.

This feature also saves configuration time by eliminating the need to specify the encapsulation type when provisioning ATM PVCs and by eliminating the need to manually provision ATM PVCs each time the encapsulation type changes.

How to Configure PPPoA PPPoE Autosense on ATM PVCs

This section contains the following tasks:

Configuring PPPoA PPPoE Autosense on a PVC

Perform this task to configure PPPoA/PPPoE Autosense on a PVC.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface atm number [. subinterface-number {multipoint | point-to-point}]

4.    pvc [name] vpi/vci

5.    encapsulation aal5autoppp virtual-template number

6.    end


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 atm number [. subinterface-number {multipoint | point-to-point}]


Example:

Router(config)# interface atm 2/0.2 multipoint

 

Specifies the ATM interface and optional subinterface and enters subinterface configuration mode.

 
Step 4
pvc [name] vpi/vci


Example:

Router(config-subif)# pvc pvc1 45/54

 

Configures a PVC on the ATM interface or subinterface and enters interface-ATM-VC configuration mode.

 
Step 5
encapsulation aal5autoppp virtual-template number


Example:

Router(config-if-atm-vc)# encapsulation aal5autoppp virtual-template 3

 

Configures PPPoA/PPPoE autosense on the PVC.

  • Also specifies the virtual template interface to use to clone the new virtual-access interfaces for PPP sessions on this PVC.
 
Step 6
end


Example:

Router(config-if-atm-vc)# end

 

Ends the session and enters privileged EXEC mode.

 

Configuring PPPoA PPPoE Autosense on a VC Class

Perform this task to configure PPPoA/PPPoE autosense on a VC class.


Note
Virtual-access interfaces for PPPoE sessions are cloned from the virtual template interface specified in the VPDN group.
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    vc-class atm vc-class-name

4.    encapsulation aal5autoppp virtual-template number

5.    exit

6.    interface atm number [. subinterface-number {multipoint | point-to-point}]

7.    class-int vc-class-name

8.    end


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
vc-class atm vc-class-name


Example:

Router(config)# vc-class atm vc1

 

Creates and names a map class.

 
Step 4
encapsulation aal5autoppp virtual-template number


Example:

Router(config-vc-class)# encapsulation aal5autoppp virtual-template 4

 

Configures PPPoA/PPPoE autosense.

  • Also specifies the virtual template interface to use to clone the new virtual-access interfaces for PPP sessions on this PVC.
 
Step 5
exit


Example:

Router(config-vc-class)# exit

 

Returns to global configuration mode.

 
Step 6
interface atm number [. subinterface-number {multipoint | point-to-point}]


Example:

Router(config)# interface 2/0.2 multipoint

 

Specifies the ATM interface enters subinterface configuration mode.

 
Step 7
class-int vc-class-name


Example:

Router(config-subif)# class-int vc1

 

Applies the VC class to all VCs on the ATM interface or subinterface.

 
Step 8
end


Example:

Router(config-subif)# end

 

Ends the session and enters privileged EXEC mode.

 

Verifying PPPoA PPPoE Autosense Configuration

To verify that you have successfully configured PPPoA/PPPoE autosense, use the show running-config command in privileged EXEC mode.

Troubleshooting Tips

To troubleshoot PPP sessions establishment, use the following commands:

  • debug ppp authentication
  • debug ppp negotiation

To troubleshoot the establishment of PPP sessions that are authenticated by a RADIUS or TACACS server, use the following commands:

  • debug aaa authentication
  • debug aaa authorization

Caution

Use debug commands with extreme caution because they are CPU-intensive and can seriously impact your network.

Monitoring and Maintaining PPPoA PPPoE Autosense for ATM PVCs

Perform this task to monitor and maintain PPPoA/PPPoE autosense.

SUMMARY STEPS

1.    enable

2.    show atm pvc [ppp]

3.    show caller

4.    show interface virtual interface-number

5.    show user

6.    show vpdn


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
show atm pvc [ppp]


Example:

Router# show atm pvc ppp

 

After the client at the other end of the PVC has initiated a PPPoA session, use this command to check that the PVC contains the PPPoA session.

 
Step 3
show caller


Example:

Router# show caller

 

Displays caller information.

Use this command to:

  • View individual users and consumed resources on the NAS.
  • Inspect active call statistics for large pools of connections. (The debug commands produce too much output and tax the CPU too heavily.)
  • Display the absolute and idle times for each user. The current values for both of these settings are displayed on the tty line and the asynchronous interface. Users that have been idle for unacceptably long periods of time can be easily identified. By using this information, you can define time out policies and multiple grades of services for different users.
 
Step 4
show interface virtual interface-number


Example:

Router# show interface virtual access 1

 

Displays information about the virtual-access interface, LCP1, protocol states, and interface statistics.

  • The status of the virtual-access interface should read: Virtual-Access3 is up, line protocol is up
 
Step 5
show user


Example:

Router# show user

 

Displays information about the active lines on the router.

 
Step 6
show vpdn


Example:

Router# show vpdn

 

Displays information about active Level 2 Forwarding (L2F) Protocol tunnel and message identifiers in a VPDN2.

 
1 LCP = link control protocol.
2 VPDN = virtual private dial-up network.

Configuration Examples for Autosense for ATM PVCs

PPPoA PPPoE Autosense on an ATM PVC Example

The following example shows how to configure the NAS with PPPoA/PPPoE autosense on PVC 30/33:

! Configure PPP Autosense 
!
interface ATM 0/0/0.33 multipoint
 pvc 30/33 
  encapsulation aal5autoppp Virtual-Template1
!
! Configure PPPoE
!
vpdn enable
vpdn-group 1
 accept-dialin 
  protocol pppoe 
  virtual-template 1
!
ip cef
interface virtual-template 1
 ip unnumbered fastethernet 0/0/0
 ip route-cache cef
!
interface fastethernet 0/0/0
 ip address 10.1.1.1 255.255.255.0
!
! Enable precloning for virtual-template 1
!

virtual-template 1 pre-clone 2000

PPPoA PPPoE Autosense on a VC Class Example

The following example shows how to configure the NAS with PPPoA/PPPoE autosense on the VC class called 'MyClass'. The 'MyClass' VC class applies PPPoA/PPPoE autosense to all PVCs on the ATM 0/0/0.99 interface:.

! Configure PPP Autosense
!
vc-class ATM MyClass
 encapsulation aal5autoppp Virtual-Template1
!
interface ATM 0/0/0.99 multipoint
  class-int MyClass
  no ip directed-broadcast
  pvc 20/40
  pvc 30/33 
!
! Configure PPPoE
!
vpdn enable
vpdn-group 1
 accept-dialin 
  protocol pppoe 
  virtual-template 1
!
ip cef
interface virtual-template 1
  ip unnumbered fastethernet 0/0/0
  ip route-cache cef
!
interface fastethernet 0/0/0
 ip address 10.1.1.1 255.255.255.0
!
! Enable precloning for virtual-template 1
!

virtual-template 1 pre-clone 2000

PPPoA PPPoE Autosense on Multiple VC Classes and Virtual Templates Example

The following example shows how to handle PPPoA and PPPoE sessions separately by two virtual templates:

ip cef
vpdn enable
!
vpdn-group 1
 accept-dialin
  protocol pppoe
  virtual-template 1
pppoe limit per-mac 1
pppoe limit per-vc 1
!
virtual-template 1 pre-clone 1500
virtual-template 2 pre-clone 1000
!
interface ATM0/0/0.3 multipoint
 no ip directed-broadcast
 class-int pppauto
!
interface ATM0/0/0.9 multipoint
 ip address 10.16.40.1 255.255.0.0
 no ip directed-broadcast
!
interface Virtual-Template1
 ip unnumbered ATM0/0/0.9
 ip route-cache cef
 no ip directed-broadcast
 peer default ip address pool pool-1
 ppp authentication pap
!
interface Virtual-Template2
 ip unnumbered ATM0/0/0.9
 ip route-cache cef
 no ip directed-broadcast
 peer default ip address pool pool-2
 ppp authentication chap
!
interface fastethernet 0/0/0
 ip address 10.1.1.1 255.255.255.0
!
vc-class atm pppauto
 encapsulation aal5autoppp Virtual-Template2
!

Note
Whenever possible, it is preferable to configure PPPoA and PPPoE to use the same virtual template. Using separate virtual templates leads to the inefficient use of virtual access because the maximum number of virtual-access interfaces will have to be precloned twice: once for PPPoE and once for PPPoA. If PPPoA and PPPoE use the same virtual template, the maximum number of virtual-access interfaces can be precloned once and used for PPPoA and PPPoE as needed.

Additional References

The following sections provide references related to the Autosense of MUX/SNAP Encapsulation and PPPoA/PPPoE on ATM PVCs feature.

Related Documents

Related Topic

Document Title

Configuring PPPoA Autosense for a VC Class

Providing Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions module

WAN commands: complete command syntax, defaults, command mode, command history, usage guidelines, and examples.

Cisco IOS Wide-Area Networking Command Reference

ATM commands: complete command syntax, defaults, command mode, command history, usage guidelines, and examples.

Cisco IOS Asynchronous Transfer Mode Command Reference

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

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Feature Information for Autosense for ATM PVCs and MUX SNAP Encapsulation

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 1 Feature Information for Autosense of MUX/SNAP Encapsulation and PPPoA/PPPoE on ATM PVCs

Feature Name

Releases

Feature Information

Autosense of MUX/SNAP Encapsulation and PPPoA/PPPoE on ATM PVCs

12.2(15)B 12.2(28)SB 12.2(33)SRE

The Autosense of MUX/SNAP Encapsulation and PPPoA/PPPoE on ATM PVCs feature enhances PPP over ATM (PPPoA)/PPP over Ethernet (PPPoE) autosense functionality by providing autosense support on MUX- and SNAP-encapsulated ATM permanent virtual circuits (PVCs).

The following commands were introduced or modified: encapsulation aal5autoppp virtual-template

Glossary

cloning --Creating and configuring a virtual-access interface by applying a specific virtual template interface. The template is the source of the generic user information and router-dependent information. The result of cloning is a virtual-access interface configured with all the commands in the template.

LCP --Link control protocol. Protocol that establishes, configures, and tests data-link connections for use by PPP.

NAS --Network access server. A device providing local network access to users across a remote access network such as the Public Switched Telephone Network (PSTN).

PPP --Point-to-Point Protocol. A protocol that encapsulates network layer protocol information over point-to-point links. PPP is defined in RFC 1661.

PPPoA --PPP over ATM.

PPPoE --PPP over Ethernet.

precloning --Cloning a specified number of virtual-access interfaces from a virtual template at system startup or when the command is configured.

PVC --Permanent virtual circuit (or connection). Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and teardown in situations where certain virtual circuits must exist all the time. In ATM terminology, called a permanent virtual connection.

VC --Virtual channel. Logical circuit created to ensure reliable communication between two network devices. A VC is defined by a VPI/VCI pair and can be either permanent (PVC) or switched (SVC).

virtual-access interface --Instance of a unique virtual interface that is created dynamically and exists temporarily. Virtual-access interfaces can be created and configured differently by different applications, such as virtual profiles and virtual private dialup networks. Virtual-access interfaces are cloned from virtual template interfaces.

virtual template interface --A logical interface configured with generic configuration information for a specific purpose or configuration common to specific users, plus router-dependent information. The template takes the form of a list of Cisco IOS interface commands that are applied to virtual-access interfaces, as needed.

VPDN --virtual private dial-up network. A system that permits dial-in networks to exist remotely from home networks, while giving the appearance of being directly connected.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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