MPLS: Layer 3 VPNs Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
MPLS VPN per Customer Edge (CE) Label
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MPLS VPN per Customer Edge (CE) Label

MPLS VPN per Customer Edge (CE) Label

The MPLS VPN per Customer Edge (CE) Label feature allows you to configure a single VPN label at the provider edge (PE) for every immediate next hop or set of next hops.

You can enable (or disable) the MPLS VPN per CE Label feature in global configuration mode.

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 MPLS VPN per CE Label

  • If your virtual routing and forwarding (VRF) domain has any of the following features enabled, disable them before you configure the MPLS VPN per CE Label feature:
    • External Border Gateway Protocol (EBGP) multipath feature
    • Internal Border Gateway Protocol (IBGP) multipath feature
    • Carrier Supporting Carrier (CSC) feature
  • Before configuring Multiprotocol Label Switching (MPLS) Layer 3 VPNs, you must install MPLS, Label Distribution Protocol (LDP), and Cisco Express Forwarding in your network. All devices in the core, including the provider edge (PE) devices, must be able to support Cisco Express Forwarding and MPLS forwarding.

Restrictions for MPLS VPN per CE Label

  • Enabling the MPLS VPN per CE Label feature causes Border Gateway Protocol (BGP) reconvergence, which can result in data loss for traffic coming from the Multiprotocol Label Switching (MPLS) VPN core.

    Note


    You can minimize network disruption by enabling this feature during a scheduled MPLS maintenance window. Also, if possible, avoid enabling this feature on a live device.


  • IPv6 Provider Edge devices (6PE) are not supported.
  • Prefix-Independent Convergence (PIC) is not supported. Per CE Label with only multipath is supported. You cannot use this feature with:
    • Internal Border Gateway Protocol (IBGP) multipath feature
    • Carrier Supporting Carrier (CSC) feature
  • When per CE label is configured, MPLS Forwarding Infrastructure (MFI) has to back up key and label information to a standby device. This will impact software downgrades.
  • The BGP Best External feature provides the network with a backup external route to avoid loss of connectivity of the primary external route. This feature is not supported.
  • Importing routes from protocols other than BGP on a PE device is not supported.
  • Any network with a zero next hop is assigned one label per network, because the next hop cannot be reliably determined.
  • Do not use per CE labels if there are multiple neighbors with the same address in a VRF domain.
  • Only single hop EBGP is supported. Multihop EBGP is not supported.
  • In high availability configurations, labels will be preserved after switchover from standby only if BGP Graceful Restart is configured before establishing BGP sessions.

Information About MPLS VPN per CE Label

MPLS VPN per CE Label Functionality

The provider edge (PE) devices store both local and remote routes and include a label entry for each route. For distributed platforms, the per-prefix labels consume memory. When there are many virtual routing and forwarding (VRF) domains and routes, the amount of memory that the per-prefix labels consume can become an issue. The purpose of using per CE label allocation is to avoid an additional lookup on the PE device's routing table and to conserve label space.

The MPLS VPN per CE Label feature allows the same label to be used for all the routes advertised from a unique customer edge (CE) peer device. The PE device allocates one label for every immediate next hop (in most cases, the next hop is a CE router). The label is directly mapped to the next hop so there is no VRF route lookup performed during data forwarding. However, the number of labels allocated is one for each CE rather than one for each prefix. As BGP is aware of all the next hops, it assigns a label for each next hop (not for each PE-CE interface).

How to Configure MPLS VPN per CE Label

Configuring the per CE Label Feature

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    mpls label mode {vrf vrf-name | all-vrfs} protocol {bgp-vpnv4 | bgp-vpnv6 | all-afs} {per-ce}

    4.    end

    5.    show ip vrf detail

    6.    show mpls forwarding-table


DETAILED STEPS
      Command or Action Purpose
    Step 1 enable


    Example:
    Device> enable
     

    Enters privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 mpls label mode {vrf vrf-name | all-vrfs} protocol {bgp-vpnv4 | bgp-vpnv6 | all-afs} {per-ce}


    Example:
    Device(config)# mpls label mode all-vrfs protocol bgp-vpnv6 per-ce
     

    Configures the MPLS VPN per CE Label feature.

     
    Step 4 end


    Example:
    Device(config)# end
     

    Exits global configuration mode and returns to privileged EXEC mode.

     
    Step 5 show ip vrf detail


    Example:
    Device# show ip vrf detail
     

    Displays the VRF label mode.

     
    Step 6 show mpls forwarding-table


    Example:
    Device# show mpls forwarding-table
     

    Displays the contents of the Multiprotocol Label Switching (MPLS) Label Forwarding Information Base (LFIB).

     

    Configuration Examples for MPLS VPN per CE Label

    Examples: MPLS VPN per CE Label

    Device> enable
    Device# configure terminal
    Device(config)# mpls label mode all-vrfs protocol bgp-vpnv6 per-ce
    Device(config)# end
    

    You can use show commands to view information about a per CE label configuration.

    The following example shows how to display detailed information about the defined VPN routing and forwarding (VRF) instances and associated interfaces:

    PE1# show ip vrf detail
    
    VRF red (VRF Id = 1); default RD 1:1; default VPNID <not set="">
      New CLI format, supports multiple address-families
      Flags: 0x180C
      Interfaces:
        Et1/0                    Et2/0                   
    VRF Table ID = 1
      Flags: 0x0
      Export VPN route-target communities
        RT:1:1                  
      Import VPN route-target communities
        RT:1:1                  
      No import route-map
      No global export route-map
      No export route-map
      VRF label distribution protocol: not configured
      VRF label allocation mode: per-ce

    The following example shows how to display the contents of the MPLS Label Forwarding Information Base (LFIB):

    PE1# show mpls forwarding-table
            
    Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
    Label      Label      or Tunnel Id     Switched      interface              
    16         Pop Label  1.1.1.1/32       0             Et0/0      10.0.0.1    
    18         No Label   nh-id(1)         0             Et2/0      10.0.2.2    
    19         No Label   nh-id(2)         0             Et1/0      10.0.1.2    
    20         No Label   nh-id(3)         0             Et1/0      10.0.1.2    
    22         No Label   nh-id(5)         0             Et1/0      10.0.1.2    
               No Label   nh-id(5)         0             Et2/0      10.0.2.2    

    Additional References

    Related Documents

    Standards and RFCs

    Standard/RFC

    Title

    RFC 2547

    BGP/MPLS

    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 MPLS VPN per CE Label

    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 MPLS VPN per CE Label

    Feature Name

    Releases

    Feature Information

    MPLS VPN per CE Label

    Cisco IOS XE Release 3.10S

    The MPLS VPN per CE Label feature allows you to configure a single VPN label at the provider edge (PE) for every immediate next hop or set of next hops.

    The following commands were introduced or modified: show mpls forwarding-table, mpls label mode.