Asynchronous Transfer Mode Configuration Guide, Cisco IOS Release 15S
Autosense of ATM PVCs and MUX SNAP Encapsulation
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Autosense of ATM PVCs and MUX SNAP Encapsulation

Autosense of ATM PVCs and MUX SNAP Encapsulation

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 caveats and feature information, see Bug Search Tool and 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 module.

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 ActionPurpose
    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 ActionPurpose
      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 ActionPurpose
        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.