Layer 2 Local Switching

Last Updated: October 6, 2011

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

The following same-port switching features are supported:

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

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.

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.

Information About Layer 2 Local Switching

Layer 2 Local Switching Overview

Local switching allows you to switch Layer 2 data between two interfaces (for example, Ethernet to Ethernet, 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

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.

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 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 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 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 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.

Perform this task to configure ATM-to-ATM PVC local switching and same-port switching.

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 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 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
pvc vpi / vci l2transport


Example:

Router(config-if)# pvc 1/200 l2transport

 

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

  • The l2transportkeyword 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 0/100 atm2/0/0 0/100

 

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.

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 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 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



Example:

atm1/0 100 atm2/0 200

 

In global configuration mode, 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 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 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.

 

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 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 NSF SSO Ethernet Port Mode to Ethernet VLAN Local Switching

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

Figure 1 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 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 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 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

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.

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.

Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)

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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