MPLS Static Labels

This document describes the Cisco MPLS Static Labels feature. The MPLS Static Labels feature provides the means to configure statically:

  • The binding between a label and an IPv4 prefix

  • The contents of an LFIB crossconnect entry

Finding Feature Information

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Restrictions for MPLS Static Labels

  • The trouble shooting process for MPLS static labels is complex.

  • On a provider edge (PE) router for MPLS VPNs, there is no mechanism for statically binding a label to a customer network prefix (VPN IPv4 prefix).

  • MPLS static crossconnect labels remain in the LFIB even if the router to which the entry points goes down.

  • MPLS static crossconnect mappings remain in effect even with topology changes.

  • MPLS static labels are not supported for label-controlled Asynchronous Transfer Mode (lc-atm).

  • MPLS static bindings are not supported for local prefixes.

Prerequisites for MPLS Static Labels

The network must support the following Cisco IOS features before you enable MPLS static labels:

  • Multiprotocol Label Switching (MPLS)

  • Cisco Express Forwarding

Information About MPLS Static Labels

MPLS Static Labels Overview

Generally, label switching routers (LSRs) dynamically learn the labels they should use to label-switch packets by means of label distribution protocols that include:

  • Label Distribution Protocol (LDP), the Internet Engineering Task Force (IETF) standard, used to bind labels to network addresses

  • Resource Reservation Protocol (RSVP) used to distribute labels for traffic engineering (TE)

  • Border Gateway Protocol (BGP) used to distribute labels for Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs)

To use a learned label to label-switch packets, an LSR installs the label into its Label Forwarding Information Base (LFIB).

The MPLS Static Labels feature provides the means to configure statically:

  • The binding between a label and an IPv4 prefix

  • The contents of an LFIB crossconnect entry

Benefits of MPLS Static Labels

Static Bindings Between Labels and IPv4 Prefixes

Static bindings between labels and IPv4 prefixes can be configured to support MPLS hop-by-hop forwarding through neighbor routers that do not implement LDP label distribution.

Static Crossconnects

Static crossconnects can be configured to support MPLS Label Switched Path (LSP) midpoints when neighbor routers do not implement either the LDP or RSVP label distribution, but do implement an MPLS forwarding path.

How to Configure MPLS Static Labels

Configuring MPLS Static Prefix Label Bindings

To configure MPLS static prefix/label bindings, use the following commands beginning in global configuration mode:

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    mpls label range min-label max-label [static min-static-label max-static-label]

    4.    mpls static binding ipv4 prefix mask [input| output nexthop] label


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 mpls label range min-label max-label [static min-static-label max-static-label]


    Example:
    Router(config)# mpls label range 200 100000 static 16 199
     

    Specifies a range of labels for use with MPLS Static Labels feature.

    (Default is no labels reserved for static assignment.)

     
    Step 4 mpls static binding ipv4 prefix mask [input| output nexthop] label


    Example:
    Router(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 55
     

    Specifies static binding of labels to IPv4 prefixes.

    Bindings specified are installed automatically in the MPLS forwarding table as routing demands.

     

    Verifying MPLS Static Prefix Label Bindings

    To verify the configuration for MPLS static prefix/label bindings, use this procedure:

    SUMMARY STEPS

      1.    Enter show mpls label range command. The output shows that the new label ranges do not take effect until a reload occurs:

      2.    Enter the show mpls static binding ipv4 command to show the configured static prefix/label bindings:

      3.    Use the show mpls forwarding-table command to determine which static prefix/label bindings are currently in use for MPLS forwarding.


    DETAILED STEPS
      Step 1   Enter show mpls label range command. The output shows that the new label ranges do not take effect until a reload occurs:

      Example:
      Router# show mpls label range
 
Downstream label pool: Min/Max label: 16/100000
   [Configured range for next reload: Min/Max label: 200/100000]
Range for static labels: Min/Max/Number: 16/199

      The following output from the show mpls label range command, executed after a reload, indicates that the new label ranges are in effect:



      Example:
      Router# show mpls label range
 
Downstream label pool: Min/Max label: 200/100000
Range for static labels: Min/Max/Number: 16/199

      Step 2   Enter the show mpls static binding ipv4 command to show the configured static prefix/label bindings:

      Example:
      Router# show mpls static binding ipv4
10.17.17.17/32: Incoming label: 251 (in LIB)
  Outgoing labels:
     10.0.0.1                  18
10.18.18.18/32: Incoming label: 201 (in LIB)
  Outgoing labels: 
10.0.0.1	implicit-null

      Step 3   Use the show mpls forwarding-table command to determine which static prefix/label bindings are currently in use for MPLS forwarding.

      Example:
      Router# show mpls forwarding-table
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop    
tag    tag or VC   or Tunnel Id      switched   interface              
201    Pop tag     10.18.18.18/32    0          PO1/1/0    point2point  
       2/35        10.18.18.18/32    0          AT4/1/0.1  point2point  
251    18          10.17.17.17/32    0          PO1/1/0    point2point

      Configuring MPLS Static Crossconnects

      To configure MPLS static crossconnects, use the following command beginning in global configuration mode:

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    mpls label range min-label max-label [static min-static-label max-static-label]

        4.    mpls static binding ipv4 prefix mask [input| output nexthop] label


      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 mpls label range min-label max-label [static min-static-label max-static-label]


        Example:
        Router(config)# mpls label range 200 100000 static 16 199
         

        Specifies a range of labels for use with MPLS Static Labels feature.

        (Default is no labels reserved for static assignment.)

         
        Step 4 mpls static binding ipv4 prefix mask [input| output nexthop] label


        Example:
        Router(config)# Router(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 55
         

        Specifies static binding of labels to IPv4 prefixes.

        Bindings specified are installed automatically in the MPLS forwarding table as routing demands.

         

        Verifying MPLS Static Crossconnect Configuration

        To verify the configuration for MPLS static crossconnects, use this procedure:

        SUMMARY STEPS

          1.    Use the show mpls static crossconnect command to display information about crossconnects that have been configured:


        DETAILED STEPS
        Use the show mpls static crossconnect command to display information about crossconnects that have been configured:

        Example:
        Router# show mpls static crossconnect
Local  Outgoing    Outgoing   Next Hop    
label  label       interface              
34     22          pos3/0/0   point2point  (in LFIB)

        Monitoring and Maintaining MPLS Static Labels

        To monitor and maintain MPLS static labels, use one or more of the following commands:

        SUMMARY STEPS

          1.    enable

          2.    show mpls forwarding-table

          3.    show mpls label range

          4.    show mpls static binding ipv4

          5.    show mpls static crossconnect


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Router> enable
           

          Enables privileged EXEC mode.

          • Enter your password if prompted.

           
          Step 2 show mpls forwarding-table


          Example:
          Router# show mpls forwarding-table
           

          Displays the contents of the MPLS LFIB.

           
          Step 3 show mpls label range


          Example:
          Router# show mpls label range
           

          Displays information about the static label range.

           
          Step 4 show mpls static binding ipv4


          Example:
          Router# show mpls static binding ipv4
           

          Displays information about the configured static prefix/label bindings.

           
          Step 5 show mpls static crossconnect


          Example:
          Router# show mpls static crossconnect
           

          Displays information about the configured crossconnects.

           

          Configuration Examples for MPLS Static Labels

          Example Configuring MPLS Static Prefixes Labels

          In the following output, the mpls label range command reconfigures the range used for dynamically assigned labels from 16 to 100000 to 200 to 100000 and configures a static label range of 16 to 199.

          Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# mpls label range 200 100000 static 16 199
% Label range changes take effect at the next reload.
Router(config)# end

          In the following output, the show mpls label range command indicates that the new label ranges do not take effect until a reload occurs:

          Router# show mpls label range
 
Downstream label pool: Min/Max label: 16/100000
   [Configured range for next reload: Min/Max label: 200/100000]
Range for static labels: Min/Max/Number: 16/199

          In the following output, the show mpls label range command, executed after a reload, indicates that the new label ranges are in effect:

          Router# show mpls label range
 
Downstream label pool: Min/Max label: 200/100000
Range for static labels: Min/Max/Number: 16/199

          In the following output, the mpls static binding ipv4 commands configure static prefix/label bindings. They also configure input (local) and output (remote) labels for various prefixes:

          Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 55
Router(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 output 10.0.0.66 2607
Router(config)# mpls static binding ipv4 10.6.0.0 255.255.0.0 input 17
Router(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 output 10.13.0.8 explicit-null
Router(config)# end

          In the following output, the show mpls static binding ipv4 command displays the configured static prefix/label bindings:

          Router# show mpls static binding ipv4
 
10.0.0.0/8: Incoming label: none;
  Outgoing labels:
10.13.0.8           explicit-null
10.0.0.0/8: Incoming label: 55 (in LIB)
  Outgoing labels:
     10.0.0.66              2607
10.66.0.0/16: Incoming label: 17 (in LIB)
  Outgoing labels:  None

          Example Configuring MPLS Static Crossconnects

          In the following output, the mpls static crossconnect command configures a crossconnect from incoming label 34 to outgoing label 22 out interface pos3/0/0:

          Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# mpls static crossconnect 34 pos3/0/0 22
Router(config)# end

          In the following output, the show mpls static crossconnect command displays the configured crossconnect:

          Router# show mpls static crossconnect
Local  Outgoing    Outgoing   Next Hop    
label  label       interface              
34     22          pos3/0/0   point2point  (in LFIB)

          Additional References

          Related Documents

          Related Topic

          Document Title

          Cisco IOS commands

          Cisco IOS Master Commands List, All Releases

          MPLS commands

          Multiprotocol Label Switching Command Reference

          Standards

          Standard

          Title

          No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

          --

          MIBs

          MIB

          MIBs Link

          No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

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

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

          RFCs

          RFC

          Title

          No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

          --

          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 Static Labels

          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 Static Labels

          Feature Name

          Releases

          Feature Information

          MPLS Static Labels

          Cisco IOS XE Release 2.1

          The MPLS Static Labels feature provides the means to configure the following items statically:

          • The binding between a label and an IPv4 prefix

          • The contents of an LFIB crossconnect entry

          The following commands were introduced or modified: debug mpls static binding, mpls label range, mpls static binding ipv4, mpls static crossconnect, show mpls label range, show mpls static binding ipv4, show mpls static crossconnect

          Glossary

          BGP --Border Gateway Protocol. The predominant interdomain routing protocol used in IP networks.

          Border Gateway Protocol --See BGP.

          FIB --Forwarding Information Base. A table that contains a copy of the forwarding information in the IP routing table.

          Forwarding Information Base --See FIB.

          label --A short, fixed-length identifier that tells switching nodes how the data (packets or cells) should be forwarded.

          label binding --An association between a label and a set of packets, which can be advertised to neighbors so that a label switched path can be established.

          Label Distribution Protocol --See LDP.

          Label Forwarding Information Base --See LFIB.

          label imposition --The act of putting the first label on a packet.

          label switching router --See LSR.

          LDP --Label Distribution Protocol. The protocol that supports MPLS hop-by-hop forwarding by distributing bindings between labels and network prefixes.

          LFIB --Label Forwarding Information Base. A data structure in which destinations and incoming labels are associated with outgoing interfaces and labels.

          LSR --label switching router. A Layer 3 router that forwards a packet based on the value of an identifier encapsulated in the packet.

          MPLS --Multiprotocol Label Switching. An industry standard on which label switching is based.

          MPLS hop-by-hop forwarding --The forwarding of packets along normally routed paths using MPLS forwarding mechanisms.

          Multiprotocol Label Switching --See MPLS.

          Resource Reservation Protocol --See RSVP.

          RIB --Routing Information Base. A common database containing all the routing protocols running on a router.

          Routing Information Base --See RIB.

          RSVP --Resource Reservation Protocol. A protocol for reserving network resources to provide quality of service guarantees to application flows.

          traffic engineering --Techniques and processes used to cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods were used.

          Virtual Private Network --See VPN.

          VPN --Virtual Private Network. A network that enables IP traffic to use tunneling to travel securely over a public TCP/IP network.