MPLS Static Labels
This document describes the Cisco MPLS Static Labels feature. The MPLS Static Labels feature provides the means to configure statically:
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The binding between a label and an IPv4 prefix
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The contents of an LFIB crossconnect entry
Prerequisites for MPLS Static Labels
The network must support the following Cisco IOS features before you enable MPLS static labels:
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Multiprotocol Label Switching (MPLS)
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Cisco Express Forwarding
Restrictions for MPLS Static Labels
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The trouble shooting process for MPLS static labels is complex.
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On a provider edge (PE) router for MPLS VPNs, there’s no mechanism for statically binding a label to a customer network prefix (VPN IPv4 prefix).
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MPLS static crossconnect labels remain in the LFIB even if the router to which the entry points goes down.
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MPLS static crossconnect mappings remain in effect even with topology changes.
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MPLS static labels aren’t supported for label-controlled Asynchronous Transfer Mode (lc-atm).
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MPLS static bindings aren’t supported for local prefixes.
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. They do this by means of label distribution protocols that include:
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Label Distribution Protocol (LDP), the Internet Engineering Task Force (IETF) standard, used to bind labels to network addresses.
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Resource Reservation Protocol (RSVP) used to distribute labels for traffic engineering (TE)
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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:
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The binding between a label and an IPv4 prefix
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The contents of an LFIB crossconnect entry
Benefits of MPLS Static Labels
Static Bindings Between Labels and IPv4 Prefixes
You can configure static bindings between labels and IPv4 prefixes to support MPLS hop-by-hop forwarding through neighbor routers that don’t implement LDP label distribution.
Static Crossconnects
You can configure static crossconnects to support MPLS Label Switched Path (LSP) midpoints when neighbor routers don’t 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
- enable
- configure terminal
- mpls label range min-label max-label [static min-static-label max-static-label ]
- mpls static binding ipv4 prefix mask [input | output nexthop ] label
DETAILED STEPS
Command or Action | Purpose | |
---|---|---|
Step 1 |
enable Example:
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Enables privileged EXEC mode. Enter your password if prompted. |
Step 2 |
configure terminal Example:
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Enters global configuration mode. |
Step 3 |
mpls label range min-label max-label [static min-static-label max-static-label ] Example:
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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:
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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
- Enter show mpls label range command. The output shows that the new label ranges do not take effect until a reload occurs:
- Enter the show mpls static binding ipv4 command to show the configured static prefix/label bindings:
- 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:
The following output from the show mpls label range command, executed after a reload, indicates that the new label ranges are in effect: Example:
|
Step 2 |
Enter the show mpls static binding ipv4 command to show the configured static prefix/label bindings: Example:
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Step 3 |
Use the show mpls forwarding-table command to determine which static prefix/label bindings are currently in use for MPLS forwarding. Example:
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Monitoring and Maintaining MPLS Static Labels
To monitor and maintain MPLS static labels, use one or more of the following commands:
SUMMARY STEPS
- enable
- show mpls forwarding-table
- show mpls label range
- show mpls static binding ipv4
- show mpls static crossconnect
DETAILED STEPS
Command or Action | Purpose | |
---|---|---|
Step 1 |
enable Example:
|
Enables privileged EXEC mode. Enter your password if prompted. |
Step 2 |
show mpls forwarding-table Example:
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Displays the contents of the MPLS LFIB. |
Step 3 |
show mpls label range Example:
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Displays information about the static label range. |
Step 4 |
show mpls static binding ipv4 Example:
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Displays information about the configured static prefix/label bindings. |
Step 5 |
show mpls static crossconnect Example:
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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 16–100000 to 200–100000. It configures a static label range of 16–199.
Device# 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 don’t take effect until a reload occurs:
Device# 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:
Device# 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:
Device# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Device(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 55
Device(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 output 10.0.0.66 2607
Device(config)# mpls static binding ipv4 10.6.0.0 255.255.0.0 input 17
Device(config)# mpls static binding ipv4 10.0.0.0 255.0.0.0 output 10.13.0.8 explicit-null
Device(config)# end
In the following output, the show mpls static binding ipv4 command displays the configured static prefix/label bindings:
Device# 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
Additional References
Related Documents
Related Topic |
Document Title |
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MPLS commands |
Multiprotocol Label Switching Command Reference |
Standards
Standard |
Title |
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No new or modified standards are supported by this feature. Support for existing standards has not been modified by this feature. |
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MIBs
MIB |
MIBs Link |
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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: |
RFCs
RFC |
Title |
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No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
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Technical Assistance
Description |
Link |
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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. |
Feature History for MPLS Static Labels
This table provides release and related information for features explained in this module.
These features are available on all releases subsequent to the one they were introduced in, unless noted otherwise.
Release |
Feature |
Feature Information |
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Cisco IOS XE Gibraltar 16.11.1 |
MPLS Static Labels |
The MPLS Static Labels feature provides the means to configure the binding between a label and an IPv4 prefix statically. The following commands were introduced or modified: debug mpls static binding , mpls label range , mpls static binding ipv4 , show mpls label range , show mpls static binding ipv4 |
Use Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn.