Layer 2 Local Switching

The Layer 2 Local Switching feature allows you to switch Layer 2 data in two ways:

  • Between two interfaces on the same router

  • Between two circuits on the same interface port, which is called same-port switching

The following interface-to-interface switching combinations are supported by this feature:

  • ATM to ATM

  • ATM to Ethernet

  • Ethernet/Ethernet VLAN to Ethernet/Ethernet VLAN

  • Frame Relay to Frame Relay

The following same-port switching features are supported:

  • ATM Permanent Virtual Circuit (PVC) and Permanent Virtual Path (PVP)

  • Ethernet VLAN

  • Frame Relay

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.

Prerequisites for Layer 2 Local Switching

You must enable Cisco Express Forwarding for the Cisco ASR 1000 Series Aggregation Services Router.

Restrictions for Layer 2 Local Switching

  • For Ethernet/Ethernet VLAN circuits, the Cisco ASR 1000 Series Aggregation Services Router must have Ethernet Adapters.

  • For Frame Relay local switching, you must globally issue the frame-relay switching command.

Information About Layer 2 Local Switching

Layer 2 Local Switching Overview

Local switching allows you to switch Layer 2 data between two interfaces of the same type (for example, Ethernet to Ethernet or Frame Relay to Frame Relay) or between interfaces of different types (for example, Ethernet VLAN to Ethernet VLAN or Ethernet to Ethernet VLAN) on the same router. The interfaces can be on the same line card or on two different cards. During these kinds of switching, the Layer 2 address is used, not the Layer 3 address.

Additionally, same-port local switching allows you to switch Layer 2 data between two circuits on the same interface.

NSF SSO—Local Switching Overview

Nonstop forwarding (NSF) and stateful switchover (SSO) improve the availability of the network by providing redundant Route Processors and checkpointing of data to ensure minimal packet loss when the primary Route Processor goes down. NSF/SSO support is available for the following locally switched attachment circuits:

  • Ethernet/Ethernet VLAN to Ethernet/Ethernet VLAN

  • Frame Relay to Frame Relay

Layer 2 Local Switching Applications

Incumbent local exchange carriers (ILECs) that use an interexchange carrier (IXC) to carry traffic between two local exchange carriers can use the Layer 2 Local Switching feature. Telecom regulations require the ILECs to pay the IXCs to carry that traffic. At times, the ILECs cannot terminate customer connections that are in different local access and transport areas (LATAs). In other cases, customer connections terminate in the same LATA, which may also be on the same router.

For example, company A has more than 50 LATAs across the country and uses three routers for each LATA. Company A uses companies B and C to carry traffic between local exchange carriers. Local switching of Layer 2 frames on the same router might be required.

Similarly, if a router is using, for example, a channelized interface, it might need to switch incoming and outgoing traffic across two logical interfaces that reside on a single physical port. The same-port local switching feature addresses that implementation.

The figure below shows a network that uses local switching for both Frame Relay to Frame Relay and ATM to Frame Relay local switching.

Figure 1. Local Switching Example

How to Configure Layer 2 Local Switching

Configuring Ethernet VLAN Same-Port Switching

Perform this task to configure Ethernet VLAN same-port switching.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface fastethernet slot / port . subinterface-number

    4.    encapsulation dot1q vlan-id

    5.    exit

    6.    interface fastethernet slot / port . subinterface-number

    7.    encapsulation dot1q vlan-id

    8.    exit

    9.    connect connection-name type number type number


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 fastethernet slot / port . subinterface-number


    Example:
    Router(config)# interface fastethernet6/0.1
     

    Specifies the first Fast Ethernet line card, subslot (if available), port, and subinterface, and enters subinterface configuration mode.

     
    Step 4 encapsulation dot1q vlan-id


    Example:
    Router(config-subif)# encapsulation dot1q 10
     

    Enables the subinterface to accept 802.1Q VLAN packets and specifies the first VLAN.

     
    Step 5 exit


    Example:
    Router(config-subif)# exit
     

    Exits subinterface configuration mode and returns to global configuration mode.

     
    Step 6 interface fastethernet slot / port . subinterface-number


    Example:
    Router(config)# interface fastethernet6/0.2
     

    Specifies the second Fast Ethernet line card, subslot (if available), port, and subinterface, and enters subinterface configuration mode.

     
    Step 7 encapsulation dot1q vlan-id


    Example:
    Router(config-subif)# encapsulation dot1q 20
     

    Enables the subinterface to accept 802.1Q VLAN packets and specifies the second VLAN.

     
    Step 8 exit


    Example:
    Router(config-subif)# exit
     

    Exits subinterface configuration mode and returns to global configuration mode.

     
    Step 9 connect connection-name type number type number


    Example:
    Router(config)# connect conn fastethernet 6/0.1 fastethernet 6/0.2
     

    Creates a local connection between the two subinterfaces (and hence their previously specified VLANs) on the same Fast Ethernet port.

     

    Configuring Ethernet Port Mode to Ethernet VLAN Local Switching

    Perform this task to configure local switching for Ethernet (port mode) to Ethernet VLAN.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface fastethernet slot / subslot / port

      4.    interface fastethernet slot / port / subinterface-number

      5.    encapsulation dot1q vlan-id

      6.    exit

      7.    connect connection-name type number type number


    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 fastethernet slot / subslot / port


      Example:
      Router(config)# interface fastethernet3/0/0
       

      Specifies a Fast Ethernet line card, subslot (if available), and port, and enters interface configuration mode.

      • This is the interface on one side of the PE router that passes Ethernet packets to and from the customer edge (CE) router.

       
      Step 4 interface fastethernet slot / port / subinterface-number


      Example:
      Router(config-if)# interface fastethernet6/0/0.1
       

      Specifies a Fast Ethernet line card, subslot (if available), port, and subinterface, and enters subinterface configuration mode.

      • This is the interface on the other side of the PE router than passes Ethernet VLAN packets to and from the CE router.

       
      Step 5 encapsulation dot1q vlan-id


      Example:
      Router(config-subif)# encapsulation dot1q 100
       

      Enables the interface to accept 802.1Q VLAN packets.

       
      Step 6 exit


      Example:
      Router(config-subif)# exit
       

      Exits subinterface configuration mode and returns to global configuration mode.

       
      Step 7 connect connection-name type number type number


      Example:
      Router(config)# connect eth-ethvlan-con fastethernet 3/0/0 fastethernet 6/0/0.1
       

      Creates a local connection between the two interfaces.

       

      Configuring ATM-to-ATM PVC Local Switching and Same-Port Switching

      You can configure local switching for both ATM AAL5 and ATM AAL0 encapsulation types.

      Creating the ATM PVC is not required. If you do not create a PVC, one is created for you. For ATM-to-ATM local switching, the autoprovisioned PVC is given the default encapsulation type AAL0 cell relay.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    interface atm slot / port

        4.    pvc vpi / vci l2transport

        5.    encapsulation layer-type

        6.    exit

        7.    exit

        8.    connect connection-name interface pvc interface pvc


      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 slot / port


        Example:
        Router(config)# interface atm1/0/0
         

        Specifies an ATM line card, subslot (if available), and port, and enters interface configuration mode.

         
        Step 4 pvc vpi / vci l2transport


        Example:
        Router(config-if)# pvc 1/100 l2transport
         

        Assigns a VPI and VCI and enters ATM PVC l2transport configuration mode.

        • The l2transport keyword indicates that the PVC is a switched PVC instead of a terminated PVC.

         
        Step 5 encapsulation layer-type


        Example:
        Router(cfg-if-atm-l2trans-pvc)# encapsulation aal5
         

        Specifies the encapsulation type for the ATM PVC. Both AAL0 and AAL5 are supported.

        • Repeat Steps 3 through 5 for another ATM PVC on the same router.

         
        Step 6 exit


        Example:
        Router(cfg-if-atm-l2trans-pvc)# exit
         

        Exits PVC l2transport configuration mode and returns to interface configuration mode.

         
        Step 7 exit


        Example:
        Router(config-if)# exit
         

        Exits interface configuration mode and returns to global configuration mode.

         
        Step 8 connect connection-name interface pvc interface pvc


        Example:
        Router(config)# connect atm-con atm1/0/0 1/100 atm2/0/0 1/100
         

        Creates a local connection between the two specified permanent virtual circuits.

         

        Configuring ATM-to-ATM PVP Local Switching

        Perform this task to configure ATM-to-ATM PVP local switching.

        Starting with Cisco IOS Release 12.0(30)S, you can configure same-port switching, as detailed in the Configuring ATM PVP Same-Port Switching.

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    interface atm slot/port

          4.    atm pvp vpi l2transport

          5.    exit

          6.    exit

          7.    connect connection-name interface pvp interface pvp


        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 slot/port


          Example:
          Router(config)# interface atm1/0
           

          Specifies an ATM line card, subslot (if available), and port and enters interface configuration mode.

           
          Step 4 atm pvp vpi l2transport


          Example:
          Router(config-if)# atm pvp 100 l2transport
           

          Identifies the virtual path and enters PVP l2transport configuration mode. The l2transportkeyword indicates that the PVP is a switched PVP instead of a terminated PVP.

          • Repeat Steps 3 and 4 for another ATM permanent virtual path on the same router.

           
          Step 5 exit


          Example:
          Router(config-if-atm-l2trans-pvp)# exit
           

          Exits PVP l2transport configuration mode and returns to interface configuration mode.

           
          Step 6 exit


          Example:
          Router(config-if)# exit
           

          Exits interface configuration mode and returns to global configuration mode.

           
          Step 7 connect connection-name interface pvp interface pvp


          Example:
          Router(config)# connect atm-con atm1/0 100 atm2/0 200
           

          Creates a local connection between the two specified permanent virtual paths.

           

          Configuring ATM PVP Same-Port Switching

          Perform this task to configure ATM PVP switching on an ATM interface.

          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    interface atm slot / subslot / port

            4.    atm pvp vpi l2transport

            5.    exit

            6.    exit

            7.    connect connection-name interface pvp interface pvp


          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 slot / subslot / port


            Example:
            Router(config)# interface atm1/0/0
             

            Specifies an ATM line card, subslot (if available), and port, and enters interface configuration mode.

             
            Step 4 atm pvp vpi l2transport


            Example:
            Router(config-if)# atm pvp 100 l2transport
             

            Specifies one VPI and enters PVP l2transport configuration mode. Repeat this step for the other ATM permanent virtual path on this same port.

            • The l2transportkeyword indicates that the indicated PVP is a switched PVP instead of a terminated PVP.

             
            Step 5 exit


            Example:
            Router(config-if-atm-l2trans-pvp)# exit
             

            Exits PVP l2transport configuration mode and returns to interface configuration mode.

             
            Step 6 exit


            Example:
            Router(config-if)# exit
             

            Exits interface configuration mode and returns to global configuration mode.

             
            Step 7 connect connection-name interface pvp interface pvp


            Example:
            Router(config)# connect atm-con atm1/0/0 100 atm1/0/0 200
             

            In global configuration mode, creates the local connection between the two specified permanent virtual paths.

             

            Configuring Frame Relay-to-Frame Relay Local Switching

            For information about Frame Relay-to-Frame Relay local switching, see the Distributed Frame Relay Switching feature module.

            SUMMARY STEPS

              1.    enable

              2.    configure terminal

              3.    ip cef distributed

              4.    frame-relay switching

              5.    interface type number

              6.    encapsulation frame-relay [cisco | ietf]

              7.    frame-relay interface-dlci dlci switched

              8.    exit

              9.    exit

              10.    connect connection-name interface dlci interface dlci


            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 ip cef distributed


              Example:
              Router(config)# ip cef distributed
               

              Enables Cisco Express Forwarding operation.

               
              Step 4 frame-relay switching


              Example:
              Router(config)# frame-relay switching
               

              Enables PVC switching on a Frame Relay DCE device or a Network-to-Network Interface (NNI).

               
              Step 5 interface type number


              Example:
              Router(config)# interface serial 0
               

              Specifies a Frame Relay interface and enters interface configuration mode.

               
              Step 6 encapsulation frame-relay [cisco | ietf]


              Example:
              Router(config-if)# encapsulation frame-relay
               

              Enables Frame Relay encapsulation.

              • The default is cisco encapsulation.

              • You do not need to specify an encapsulation type.

               
              Step 7 frame-relay interface-dlci dlci switched


              Example:
              Router(config-if)# frame-relay interface-dlci 100 switched
               

              (Optional) Creates a switched PVC and enters Frame Relay DLCI configuration mode.

              • Repeat Steps 5 through 7 for each switched PVC.

              • If you do not create a Frame Relay PVC in this step, it will automatically be created by the connect command.

               
              Step 8 exit


              Example:
              Router(config-fr-dlci)# exit
               

              Exits Frame Relay DLCI configuration mode and returns to interface configuration mode.

               
              Step 9 exit


              Example:
              Router(config-if)# exit
               

              Exits interface configuration mode and returns to global configuration mode.

               
              Step 10 connect connection-name interface dlci interface dlci


              Example:
              Router(config)# connect connection1 serial0 100 serial1 101
               

              Defines a connection between Frame Relay PVCs.

               

              Verifying Layer 2 Local Switching

              Verifying Layer 2 Local Switching Configuration

              To verify configuration of the Layer 2 local switching feature, use the show connection command on the provider edge (PE) router.

              SUMMARY STEPS

                1.    show connection [all | element | id id | name name | port port]


              DETAILED STEPS
              show connection [all | element | id id | name name | port port]

              The show connectioncommand displays the local connection between a Gigabit Ethernet interface and another local Gigabit Ethernet interface:



              Example:
              Router# show connection name ethconn1
Connection: 1 - ethconn1
 Current State: UP
 Segment 1: GigabitEthernet0/0/0.1 up
 Segment 2: GigabitEthernet0/0/0.2 up

              Verifying the NSF SSO Local Switching Configuration

              Layer 2 local switching provides NSF/SSO support for Local Switching of the following attachment circuits on the same router:

              • Ethernet/Ethernet VLAN to Ethernet/Ethernet VLAN

              For information about configuring NSF/SSO on the Route Processors, see the " Stateful Switchover " module in the Cisco IOS XE High Availability Configuration Guide . Perform this task to verify that the NSF/SSO: Layer 2 Local Switching feature is working correctly.

              SUMMARY STEPS

                1.    ping

                2.    redundancy force-switchover

                3.    show connection all

                4.    ping


              DETAILED STEPS
                Step 1   ping

                Issue the pingcommand or initiate traffic between the two CE routers.

                Step 2   redundancy force-switchover

                Force the switchover from the active RP to the standby RP by using the redundancy force-switchover command. This manual procedure allows for a "graceful" or controlled shutdown of the active RP and switchover to the standby RP. This graceful shutdown allows critical cleanup to occur.

                Step 3   show connection all

                Issue the show connection allcommand to ensure that the Layer 2 local switching connection on the dual RP is operating:



                Example:
                Router# show connection all
D   Name            Segment 1              Segment 2                  State    
================================================================================
1    conn            Gi0/0/0.1              Gi0/0/0.2                  UP
                Step 4   ping

                Issue the ping command from the CE router to verify that the contiguous packet outage was minimal during the switchover.

                Troubleshooting Tips

                You can troubleshoot Layer 2 local switching using the following commands on the PE router:

                • debug conn

                • show connection

                Configuration Examples for Layer 2 Local Switching

                Example: Configuring Ethernet VLAN Same-Port Switching

                The following example shows same-port switching between two VLANs on one Ethernet interface:

                interface fastethernet 0/0.1
 encapsulation dot1q 1
interface fastethernet 0/0.2
 encapsulation dot1q 2
connect conn FastEthernet 0/0.1 FastEthernet 0/0.2

                Example: Configuring NSF SSO Ethernet Port Mode to Ethernet VLAN Local Switching

                The following configuration uses the network topology shown in the figure below.

                Figure 2. NSF/SSO: Layer 2 Local Switching: Ethernet to Ethernet VLAN

                The following example shows the configuration of the CE interfaces to connect to the PE1 router:

                CE1

                CE2 

                ip routing
                !
                interface fa3/1/0
                 description: connection to PE fa1/1/1
                 no shutdown
                 ip address 10.1.1.1 255.255.255.0
                		 
                ip routing
                !
                interface fa4/0
                 no shutdown
                !
                interface fa4/0.1
                 description: connection to PE1 fa6/0/0.1
                 encapsulation dot1Q 10
                 ip address 10.1.1.2 255.255.255.0
                !
                interface fa4/0.2
                 description - connection to PE1 fa6/0/0.2
                 encapsulation dot1Q 20
                 ip address 172.16.1.2 255.255.255.0

                The following example shows the configuration of the PE1 router with NSF/SSO and the PE interfaces to the CE routers:

                PE1 

                redundancy
                 no keepalive-enable
                 mode sso
                !
                !
                ip routing
                ip cef distributed
                !
                interface fa1/1/1
                 description - connection to CE1 fa3/1/0
                 no shutdown
                 no ip address
                !
                !
                interface fa6/0/0
                 no shutdown
                 no ip address
                !
                interface fa6/0/0.1
                 description - connection to CE2 fa4/0.1
                 encapsulation dot1Q 10
                 no ip address
                !
                interface fa6/0/0.2
                 description - connection to CE2 fa4/0.2
                 encapsulation dot1Q 20
                 no ip address

                Example: Configuring ATM-to-ATM Local Switching

                The following example shows local switching on ATM interfaces configured for AAL5:

                interface atm1/0/0
 pvc 0/100 l2transport
 encapsulation aal5
interface atm2/0/0
 pvc 0/100 l2transport
 encapsulation aal5
connect aal5-conn atm1/0/0 0/100 atm2/0/0 0/100

                Example: Configuring ATM PVC Same-Port Switching

                The following example shows same-port switching between two PVCs on one ATM interface:

                interface atm1/0/0
 pvc 0/100 l2transport
 encapsulation aal5
 pvc 0/200 l2transport
 encapsulation aal5
connect conn atm1/0/0 0/100 atm1/0/0 0/200

                Example: Configuring ATM PVP Same-Port Switching

                The following example shows same-port switching between two PVPs on one ATM interface:

                interface atm1/0/0
 atm pvp 100 l2transport
 atm pvp 200 l2transport
connect conn atm1/0/0 100 atm1/0/0 200

                Example: Configuring Frame Relay-to-Frame Relay Local Switching

                The following example shows serial interfaces configured for Frame Relay. The connect command allows local switching between these two interfaces. 

                frame-relay switching
ip cef distributed
interface serial3/0/0
 encapsulation frame-relay
 frame-relay interface-dlci 100 switched
 frame-relay intf-type dce
interface serial3/1/0
 encapsulation frame-relay ietf
 frame-relay interface-dlci 200 switched
 frame-relay intf-type dce
connect fr-con serial3/0/0 100 serial3/1/0 200

                Additional References

                Related Documents

                Related Topic

                Document Title

                Cisco IOS commands

                Cisco IOS Master Command List, All Releases

                WAN Commands

                Cisco IOS Wide-Area Networking Command Reference

                Stateful switchover configuration information

                "Stateful Switchover " module in the Cisco IOS XE High Availability Configuration Guide

                Standards

                Standard

                Title

                draft-ietf-l2tpext-l2tp-base-03.txt

                Layer Two Tunneling Protocol (Version 3) 'L2TPv3'

                draft-martini-l2circuit-trans-mpls-09.txt

                Transport of Layer 2 Frames Over MPLS

                draft-martini-l2circuit-encap-mpls-04.txt

                Encapsulation Methods for Transport of Layer 2 Frames Over IP and MPLS Networks

                draft-ietf-ppvpn-l2vpn-00.txt

                An Architecture for L2VPNs

                MIBs

                MIB

                MIBs Link

                None

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

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

                RFCs

                RFC

                Title

                None

                --

                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 Layer 2 Local Switching

                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 Layer 2 Local Switching

                Feature Name

                Releases

                Feature Information

                Layer 2 Local Switching

                Cisco IOS XE Release 2.5

                The Layer 2 Local Switching feature allows you to switch Layer 2 data between two interfaces on the same router, and in some cases to switch Layer 2 data between two circuits on the same interface port.

                In Cisco IOS XE Release 2.5, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers. Support was added for the following local switching types:
                • Ethernet to Ethernet VLAN
                • Same-port switching for Ethernet VLAN

                The following commands were introduced or modified: connect (L2VPN local switching), show connection.

                Layer 2 Local Switching - ATM to ATM

                Cisco IOS XE Release 3.3S

                In Cisco IOS XE Release 3.3S, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

                The following commands were introduced or modified: connect (L2VPN local switching), show connection.

                Layer 2 Local Switching - Frame Relay to Frame Relay

                Cisco IOS XE Release 3.9S

                In Cisco IOS XE Release 3.9S, this feature was introduced on the Cisco ISR 4400 Series Routers.