Configuring the Path Selection Metric for MPLS TE Tunnels

This chapter describes how to configure the path selection metric for Multiprotocol Label Switching (MPLS) traffic engineering (TE) tunnels on Cisco NX-OS devices.

This chapter includes the following sections:

Finding Feature Information

Your software release might not support all the features documented in this module. For the latest caveats and feature information, see the Bug Search Tool at https://tools.cisco.com/bugsearch/ and the release notes for your 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 “New and Changed Information” chapter or the Feature History table below.

Information About the Path Selection Metric for MPLS TE Tunnels

Certain tunnels carry voice traffic, which requires low delay, and other tunnels carry data.You can configure the path selection metric for TE tunnels on a global or per-tunnel basis. You can specify the TE link metric on an interface, or let it default to the IGP link metric. You can also specify the link metric for path selection for these low-delay traffic tunnels and let the other tunnels use the Interior Gateway Protocol (IGP) metric for path selection. MPLS TE supports Intermediate System-to-Intermediate System (IS-IS) and Open Shortest Path First (OSPF) as the IGP.

IGP floods two metrics for every MPLS TE link as follows:

  • IGP link metric, which is the IGP determined metric for the link.
  • Path selection metric, which is the TE link metric for the link. This metric defaults to the IGP link metric, but you can specify the TE link metric by using the mpls traffic-eng administrative-weight command on the interface.

Licensing Requirements for the Path Selection Metric for MPLS TE Tunnels

 

Product
License Requirement

Cisco NX-OS

Configurable path selection metric for tunnels requires an MPLS license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide.

Prerequisites for the Path Selection Metric for MPLS TE Tunnels

The path selection metric for MPLS TE tunnels has the following prerequisites:

Guidelines and Limitations for the Path Selection Metric for MPLS TE Tunnels

The path selection metric has the following configuration guidelines and limitations:

  • Unless explicitly configured, the TE link metric (administrative-weight) for a given link is the IGP link metric. When the TE link metric is used to represent a link property that is different from the cost/distance, you must configure every network link that can be used for TE tunnels with a TE link metric that represents that property. Failure to do so might cause tunnels to use unexpected paths.
  • You cannot configure MPLS TE over the logical generic routing encapsulation (GRE) tunnel interface.
  • MPLS TE supports only a single IGP process or instance. Multiple IGP processes or instances are not supported and you should not configure MPLS TE in more than one IGP process or instance. You might configure MPLS TE in multiple OSPF areas or both IS-IS levels.

Default Settings for the Path Selection Metric for MPLS TE Tunnels

Table 13-1 lists the default settings for the path selection metric for MPLS TE tunnels.

 

Table 13-1 Default Settings for the Path Selection Metric for MPLS TE Tunnels

Parameters
Default

Global path selection metric type

TE

Interface path selection metric type

IGP

TE tunnel interface path selection metric type

TE

TE link metric/administrative-weight

IGP link metric

Note Although both the global path selection metric and TE tunnel path selection metric default to TE, because the interface TE link metric defaults to the IGP link metric, the effective default configuration uses the IGP link metrics.

Configuring the Path Selection Metric for MPLS TE Tunnels

This section includes the following topics:

Configuring the Global Path Selection Metric Type for MPLS TE Tunnels

You can configure the path selection to use either the IGP metric or the TE metric for all MPLS TE tunnels.

Note The configured TE tunnel interface path selection metric type takes precedence over the global path selection metric type.

Prerequisites

You must have the MPLS TE feature enabled (see the “Configuring MPLS TE”).

Ensure that you are in the correct VDC (or use the switchto vdc command).

SUMMARY STEPS

1. configure terminal

2. mpls traffic-eng configuration

3. path-selection metric { igp | te }

4. (Optional) show mpls traffic-eng tunnels tunnel-te number

5. (Optional) copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1

configure terminal

 

Example:

switch# configure terminal

switch(config)#

Enters global configuration mode.

Step 2

mpls traffic-eng configuration

 

Example:

switch(config)# mpls traffic–eng configuration

switch(config-te)#

Enters MPLS TE configuration mode.

Step 3

path-selection metric { igp | te }

 

Example:

switch(config-te)# path-selection metric te

Specifies the metric type to use if a metric type is not explicitly configured for an MPLS TE tunnel. If you configure the TE path selection metric type, you can also configure the MPLS TE administrative weight on each TE tunnel. The default is IGP.

Step 4

show mpls traffic-eng tunnels tunnel-te number

 

Example:

switch(config-if-te)# show mpls traffic-eng tunnels tunnel-te 0

(Optional) Displays information about the MPLS TE tunnel configuration.

Step 5

copy running-config startup-config

 

Example:

switch(config-if-te)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Configuring the Path Selection Metric Type for a TE Tunnel

You can override the global tunnel path selection metric on a per-TE tunnel interface, and you can also override the IGP link metric on any link by configuring the TE administrative weight on that link.

SUMMARY STEPS

1. configure terminal

2. interface tunnel-te number

3. path-selection metric { igp | te }

4. (Optional) interface type/ number

5. (Optional) mpls traffic-eng administrative-weight weight

6. (Optional) show mpls traffic-eng tunnels tunnel-te number

7. (Optional) copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1

configure terminal

 

Example:

switch# configure terminal

switch(config)#

Enters global configuration mode.

Step 2

interface tunnel-te number

 

Example:

switch(config)# interface tunnel-te 1

switch(config-if-te)#

Enters TE interface configuration mode. The number range is from 0 to 65503.

Step 3

path-selection metric { igp | te }

 

Example:

switch(config-if-te)# path-selection metric te

Specifies the metric type to use for the MPLS TE tunnel path selection. The default is TE.

Step 4

interface type/nu mber

 

Example:

switch(config-if-te)# interface ethernet 2/1

switch(config-if)#

(Optional) Enters interface configuration mode. Use ? to see a list of supported interfaces.

Step 5

mpls traffic-eng administrative-weight weight

 

Example:

switch(config-if)# mpls traffic-eng administrative weight 20

(Optional) Overrides the IGP administrative weight (cost) of the link. Configure this parameter if you configured the path selection metric type as TE and you want to specify the TE link cost/administrative-weight rather than defaulting to the IGP cost.

Step 6

show mpls traffic-eng tunnels tunnel-te number

 

Example:

switch(config-if)# show mpls traffic-eng tunnels tunnel-te 0

(Optional) Displays information about the MPLS TE tunnel configuration.

Step 7

copy running-config startup-config

 

Example:

switch(config-if)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Verifying the Path Selection Metric Configuration for MPLS TE Tunnels

To display the path selection metric for MPLS TE tunnels, perform one of the following tasks:

 

Command
Purpose

show mpls traffic-eng topology

Displays the TE and IGP metrics for each link.

show mpls traffic-eng tunnels

Displays the link metric used for tunnel path selection.

show mpls traffic-eng link-management summary

Displays each link’s administrative weight and whether it was inherited from the IGP or is an override with the TE administrative weight.

For detailed information about the fields in the output from these commands, see the Cisco NX-OS MPLS Command Reference .

Configuration Examples for the Path Selection Metric for MPLS TE Tunnels

The section shows how to configure the link metric type that you can use for the tunnel path selection and how to configure the link metrics. The configuration commands included in this section allow you to specify the metric type for path selection and assign metrics to links. Additional commands are required to fully configure the example scenario. For example, you need the IGP commands to continue TE and the link interface commands to enable TE and specify the available bandwidth.

The example in this section supports the simple network technology shown in Figure 13-1.

Note This example applies only to dynamic tunnels, not to ones with an explicit path.

Figure 13-1 Network Topology

 

In Figure 13-1, the topology shows the following:

  • Tunnel1 and Tunnel2 connects from R1 (headend) to R4 (tailend).
  • Tunnel3 connects from R1 to R5.
  • The path selection for Tunnel1 and Tunnel3 should use a metric that represents a link delay because these tunnels carry voice traffic.
  • The path selection for Tunnel2 should use IGP metrics because MPLS TE carries data traffic with no delay requirement.

The following configuration fragments for each of the routers show the configuration that relates to link metrics and their use in the tunnel path selection. TE metrics that represent a link delay must be configured for the network links on each of the routers, and the three tunnels must be configured on R1.

These configuration fragments force Tunnel1 to take path R1-R3-R4, Tunnel2 to take path R1-R2-R4, and Tunnel3 to take path R1-R3-R4-R5 (if the links have sufficient bandwidth to accommodate the tunnels).

R1 Configuration

interface eth1/1
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
interface eth1/2
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
 
interface Tunnel-te 1 !Tunnel1 uses TE metric (default)
!for path selection
ip unnumbered loopback0
destination 192.168.4.4
bandwidth 1000
path-option 1 dynamic
 
interface Tunnel-te 2 !Tunnel2 uses IGP metric
!for path selection
ip unnumbered loopback0
destination 192.168.4.4
bandwidth 1000
path-option 1 dynamic
path-selection metric igp !Use IGP cost for path selection.
 
interface Tunnel 3 !Tunnel3 uses TE metric (default)
!for path selection
ip unnumbered loopback0
destination 192.168.5.5
bandwidth 1000
path-option 1 dynamic
 

R2 Configuration

interface eth1/3
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
interface eth4/1
mpls traffic-eng administrative-weight 40 !TE metric different from IGP metric
 

R3 Configuration

interface eth2/1
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
interface eth3/1
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
interface eth6/1
mpls traffic-eng administrative-weight 5 !TE metric different from IGP metric
 

R4 Configuration

interface eth2/2
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
interface eth2/1
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
interface eth2/3
mpls traffic-eng administrative-weight 5 !TE metric different from IGP metric
 

R5 Configuration

interface eth1/2
mpls traffic-eng administrative-weight 15 !TE metric different from IGP metric
interface eth1/1
mpls traffic-eng administrative-weight 5 !TE metric different from IGP metric
 

Additional References for MPLS TE Tunnels

The following sections provide references related to the path selection metric for MPLS TE tunnels.

Related Document

Related Topic
Document Title

MPLS TE commands

Cisco NX-OS Multiprotocol Label Switching Command Reference

MIBs

MIB
MIBs Link
  • CISCO-IETF-FRR-MIB
  • MPLS TE-STD-MIB

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

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

Feature History for the Path Selection Metric for MPLS TE Tunnels

Table 13-2 lists the release history for this feature.

 

Table 13-2 Feature History for the Path Selection Metric for MPLS TE Tunnels
Feature Name
Releases
Feature Information

Path selection metric

5.2(1)

This feature was introduced.