We saw in a previous post how to set up a basic MPLS Traffic Engineering tunnel, we used explicit and dynamic path which worked very well but explicit path don’t scale well and dynamic is too hazardous (you don’t really know where your traffic goes).
Hopefully for us the MPLS Traffic Engineering guys thought about it and added a function called MPLS Traffic Engineering Affinity.

I’ll be using the same setup as for MPLS traffic engineering

Diagram

Initial configuration

SPRack1R4(config-if)#do sh run int tun0
Building configuration...

Current configuration : 366 bytes
!
interface Tunnel0
 description TO-R3
 ip unnumbered Loopback0
 tunnel destination 24.1.3.3
 tunnel mode mpls traffic-eng
 tunnel mpls traffic-eng autoroute announce
 tunnel mpls traffic-eng priority 7 7
 tunnel mpls traffic-eng bandwidth  64
 tunnel mpls traffic-eng path-option 1 dynamic

This is our initial configuration, as you can see I’m only running in dynamic path.

SPRack1R4(config-if)#do sh mpls traff tun

Name: TO-R3                               (Tunnel0) Destination: 24.1.3.3
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected

    path option 1, type dynamic (Basis for Setup, path weight 10)

  Config Parameters:
    Bandwidth: 64       kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
    Metric Type: TE (default)
    AutoRoute:  enabled   LockDown: disabled  Loadshare: 64       bw-based
    auto-bw: disabled

  InLabel  :  -
  OutLabel : Serial0/0/0.1, implicit-null
  RSVP Signalling Info:
       Src 24.1.4.4, Dst 24.1.3.3, Tun_Id 0, Tun_Instance 92
    RSVP Path Info:
      My Address: 24.1.4.4
      Explicit Route: 24.1.34.3 24.1.3.3
      Record Route:  NONE
      Tspec: ave rate=64 kbits, burst=1000 bytes, peak rate=64 kbits
    RSVP Resv Info:
      Record Route:  NONE
      Fspec: ave rate=64 kbits, burst=1000 bytes, peak rate=64 kbits
  History:
    Tunnel:
      Time since created: 2 hours, 37 minutes
      Time since path change: 1 minutes, 56 seconds
    Current LSP:
      Uptime: 1 minutes, 56 seconds
      Selection: reoptimation
    Prior LSP:
      ID: path option 1 [91]
      Removal Trigger: configuration changed

And our traffic is going through the frame relay between R3 and R4.

Now we’re going to modify the traffic path without change the path configuration, we’ll just add the tunnel mpls traffic-eng affinity and create a path by configuring the interfaces with mpls traffic-eng attribute-flags

Let’s configure the Tunnel interface

interface Tunnel0
 tunnel mpls traffic-eng affinity 0x3 mask 0xFFFF

And on the traffic path

interface GigabitEthernet0/0
 mpls traffic-eng attribute-flags 0x3

This configuration is just like RSVP, you have to configure it on all the interface that the traffic will take.

And …

SPRack1R4(config-if)#do sh mpls traff tun

Name: TO-R3                               (Tunnel0) Destination: 24.1.3.3
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected

    path option 1, type dynamic (Basis for Setup, path weight 30)

  Config Parameters:
    Bandwidth: 64       kbps (Global)  Priority: 7  7   Affinity: 0x3/0xFFFF
    Metric Type: TE (default)
    AutoRoute:  enabled   LockDown: disabled  Loadshare: 64       bw-based
    auto-bw: disabled

  InLabel  :  -
  OutLabel : GigabitEthernet0/1, 21
  RSVP Signalling Info:
       Src 24.1.4.4, Dst 24.1.3.3, Tun_Id 0, Tun_Instance 93
    RSVP Path Info:
      My Address: 24.1.45.4
      Explicit Route: 24.1.45.5 24.1.56.5 24.1.56.6 24.1.36.6
                      24.1.36.3 24.1.3.3
      Record Route:  NONE
      Tspec: ave rate=64 kbits, burst=1000 bytes, peak rate=64 kbits
    RSVP Resv Info:
      Record Route:  NONE
      Fspec: ave rate=64 kbits, burst=1000 bytes, peak rate=64 kbits
  History:
    Tunnel:
      Time since created: 2 hours, 43 minutes
      Time since path change: 4 seconds
    Current LSP:
      Uptime: 4 seconds
      Selection: reoptimation
    Prior LSP:
      ID: path option 1 [92]
      Removal Trigger: configuration changed

TADA! The traffic path changed.

Now this is a simple example, if we loose any links on the path to R3 there will be no rerouting because we configured a strict mask (only affinity 0x3 as default mask is 0xFFFF).