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Lecture 11

Lecture 11. MPLS TE Application. MPLS TE application allows establishment of tunnels and forwarding of IP traffic onto tunnels. MPLS TE application uses following mechanisms: Data Plane: MPLS Control Plane: RSVP-TE Constraint-based routing: TE extended OSPF/IS-IS. IGP control messages.

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Lecture 11

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  1. Lecture 11

  2. MPLS TE Application • MPLS TE application allows establishment of tunnels and forwarding of IP traffic onto tunnels. • MPLS TE application uses following mechanisms: • Data Plane: MPLS • Control Plane: RSVP-TE • Constraint-based routing: TE extended OSPF/IS-IS

  3. IGP control messages RSVP control messages OSPF/ISIS RSVP-TE Data traffic Label switching MPLS TE Components

  4. Tunnel is created at the head end R3 R2 R5 R6 R1 R1 Tunnel R4 R3 midpoint midpoint midpoint Tail Head Tunnel Terminology

  5. TE Headend Control • TE headend is responsible for number of tunnel management tasks such as: • Configuration • Setup • Release • Maintenance (e.g., tunnel re-optimization)

  6. TE Link Management (LM) • TE LM maintains the link resource information in the database such as: • Available BW 0-7 priority levels • Link attributes (color), etc…. • On significant changes in the link resource information (e.g., crosses certain predefined thresholds), TE-LM builds the TE Opaque LSAs and hands it over to the Flooding module.

  7. IGP Flooding • IGP Flooding module floods the regular and TE Opaque LSAs through the area. • Flooding of TE Opaque LSAs is triggered by following events: • Significant changes in the link resource (e.g., reconfigured set of thresholds) • LSA periodic refresh timer expiration • On tunnel setup failure • On modification of link configured BW

  8. TE Topology DB • TE Topology DB is an extended link-state topology database which is built by using regular and TE Opaque LSAs. • In contrast with “regular” topology database, TE topology database contains more information about link attributes (e.g., bandwidth) that is needed for computing CSPF paths.

  9. TE Path Calculation • The Path Calculation module uses TE topology DB to find a path that meets certain specified constraints. • If such a path exists, the output of the Path Calculation module is used to build the ERO for establishing the tunnel. • Because path selection is performed at the headend, Path Calculation function exists at the headend node only. • Any exception? (Hint: Loose ERO)

  10. Tunnel Attributes • Source IP address (headend) • Destination IP address (tailend) • Dynamic—choose the constraint-based shortest path first tunnel • Static—use the path specified • Bandwidth—tunnel capacity • Priority—high-priority tunnels may preempt lower-priority tunnels • Link coloring—apply link attributes (affinity)

  11. TE Tunnel Setup • The Path Calculation module uses TE topology DB to find a path that meets certain specified constraints. • If such a path exists, the output of the Path Calculation module is used to build the ERO for establishing the tunnel. • Because path selection is performed at the headend, Path Calculation function exists at the headend node only. • What about midpoint? (Hint: Loose ERO)

  12. TE Tunnel Reoptimization • Once a tunnel is established, due to topology changes or other events, the current path may no longer be optimal. • The object of tunnel reoptimization is to find a better path (if one exists), and reroute the tunnel along the new path. • In order not to disrupt traffic on the existing tunnel, another tunnel is first established along the new path before tearing the old tunnel. • The above approach is commonly referred to as “make-before-break”.

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