MPLS TE Metric

When you configure MPLS TE, your IGP (OSPF or IS-IS) floods two metrics for every link:

  • IGP metric
  • TE metric

Tunnels use the TE metric by default. Also, the TE metric is the same as the shortest path IGP metric by default.

For each tunnel, you can specify whether the path calculation has to use the IGP or TE metrics.

This can be useful in a scenario where you have two traffic types. Let’s say you have VoIP traffic and regular data traffic. You could use the IGP metric for tunnels that carry data traffic and the TE metric for tunnels that carry VoIP traffic.

Here’s an example:

Mpls Te Metric Topology

In the picture above, we have two possible paths to get from PE1 to PE2:

  • Through P1
  • Through P2 and P3

By default, tunnels would use the shortest path through P1. Imagine that the path through P2 and P3 somehow has a lower delay than through P1, and we would like to use this path for VoIP traffic. We can change the TE metric on these interfaces to become the shortest path. That’s what we are going to do in this lesson.

  • Configurations
  • CE1
  • CE2
  • P1
  • P2
  • P3
  • PE1
  • PE2

Want to take a look for yourself? Here you will find the startup configuration of each device.

I use Cisco IOS Software, IOSv Software (VIOS-ADVENTERPRISEK9-M), Version 15.9(3)M4.

Configuration

We’ll configure two tunnels:

  • Tunnel 1 (Data traffic) uses the IGP metric.
  • Tunnel 2 (VoIP traffic) uses the TE metric.

Tunnel 1 (Data)

We’ll start with the data tunnel. With the show mpls traffic-eng topology command, you can see the metric of any interface in your MPLS TE topology. Here are the metrics of one of PE2’s interfaces:

PE1#show mpls traffic-eng topology 2.2.2.2

IGP Id: 0002.0002.0002.00, MPLS TE Id:2.2.2.2 Router Node  (isis  level-2) id 1
      link[0]: Broadcast, DR: 0002.0002.0002.03, nbr_node_id:6, gen:95
          frag_id 0, Intf Address:192.168.24.2
          TE metric:10, IGP metric:10, attribute flags:0x0
[output omitted]

The default IS-IS IGP metric is 10. The TE metric is the same as the IGP metric, so it’s also 10.

We can see the total metric of a path when we look at our tunnel:

PE1#show mpls traffic-eng tunnels Tunnel 1

Name: PE1_t1                              (Tunnel1) Destination: 6.6.6.6
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected
    path option 1, type dynamic (Basis for Setup, path weight 20)

  Config Parameters:
    Bandwidth: 750      kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
    Metric Type: TE (interface)
    AutoRoute:  disabled  LockDown: disabled  Loadshare: 750      bw-based
    auto-bw: disabled
  Active Path Option Parameters:
    State: dynamic path option 1 is active
    BandwidthOverride: disabled  LockDown: disabled  Verbatim: disabled


  InLabel  :  - 
  OutLabel : GigabitEthernet0/1, 16
  RSVP Signalling Info:
       Src 2.2.2.2, Dst 6.6.6.6, Tun_Id 1, Tun_Instance 244
    RSVP Path Info:
      My Address: 192.168.23.2   
      Explicit Route: 192.168.23.3 192.168.36.3 192.168.36.6 6.6.6.6 
      Record   Route:   NONE
      Tspec: ave rate=750 kbits, burst=1000 bytes, peak rate=750 kbits
    RSVP Resv Info:
      Record   Route:   NONE
      Fspec: ave rate=750 kbits, burst=1000 bytes, peak rate=750 kbits
  Shortest Unconstrained Path Info:
    Path Weight: 20 (TE)
    Explicit Route: 192.168.23.2 192.168.23.3 192.168.36.3 192.168.36.6 
                    6.6.6.6 
  History:
    Tunnel:
      Time since created: 9 days, 20 hours, 14 minutes
      Time since path change: 2 minutes, 46 seconds
      Number of LSP IDs (Tun_Instances) used: 244
    Current LSP:
      Uptime: 2 minutes, 46 seconds
    Prior LSP:
      ID: path option 1 [174]
      Removal Trigger: tunnel shutdown

In the output above, you see that we use the TE metric and that the total path metric is 20.

Let’s change this tunnel so that it uses the IGP metric instead:

PE1(config)#interface Tunnel 1
PE1(config-if)#tunnel mpls traffic-eng path-selection metric ?
  igp  Use IGP Metric
  te   Use TE Metric

I’ll select IGP:

PE1(config-if)#tunnel mpls traffic-eng path-selection metric igp

This tunnel now uses the IGP metric to calculate the shortest path. Nothing will change for this tunnel at this moment because it was already using the shortest path through P1.

Tunnel 2 (VoIP)

Let’s create the second tunnel. I’ll use the same configuration as tunnel one:

PE1(config)#interface Tunnel 2
PE1(config-if)#ip unnumbered Loopback0
PE1(config-if)#tunnel mode mpls traffic-eng
PE1(config-if)#tunnel destination 6.6.6.6
PE1(config-if)#tunnel mpls traffic-eng priority 7 7
PE1(config-if)#tunnel mpls traffic-eng bandwidth 750
PE1(config-if)#tunnel mpls traffic-eng path-option 1 dynamic

We know that by default, a MPLS TE tunnel uses the TE metric but let’s check it anyway:

PE1#show mpls traffic-eng tunnels Tunnel 2

Name: PE1_t2                              (Tunnel2) Destination: 6.6.6.6
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected
    path option 1, type dynamic (Basis for Setup, path weight 20)

  Config Parameters:
    Bandwidth: 750      kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
    Metric Type: TE (default)
    AutoRoute:  disabled  LockDown: disabled  Loadshare: 750      bw-based
    auto-bw: disabled
  Active Path Option Parameters:
    State: dynamic path option 1 is active
    BandwidthOverride: disabled  LockDown: disabled  Verbatim: disabled


  InLabel  :  - 
  OutLabel : GigabitEthernet0/1, 16
  RSVP Signalling Info:
       Src 2.2.2.2, Dst 6.6.6.6, Tun_Id 2, Tun_Instance 1
    RSVP Path Info:
      My Address: 192.168.23.2   
      Explicit Route: 192.168.23.3 192.168.36.3 192.168.36.6 6.6.6.6 
      Record   Route:   NONE
      Tspec: ave rate=750 kbits, burst=1000 bytes, peak rate=750 kbits
    RSVP Resv Info:
      Record   Route:   NONE
      Fspec: ave rate=750 kbits, burst=1000 bytes, peak rate=750 kbits
  Shortest Unconstrained Path Info:
    Path Weight: 20 (TE)
    Explicit Route: 192.168.23.2 192.168.23.3 192.168.36.3 192.168.36.6 
                    6.6.6.6 
  History:
    Tunnel:
      Time since created: 41 seconds
      Time since path change: 40 seconds
      Number of LSP IDs (Tun_Instances) used: 1
    Current LSP:
      Uptime: 40 seconds

The output above shows that the tunnel uses the TE metric and that the total path metric is 20. Now let’s change the TE metric on our interfaces. Because MPLS TE tunnels are unidirectional, I would only have to change the TE metric on these interfaces: