1. CS 672 1 Summer 2003 Lecture 11

2. CS 672 2 Summer 2003 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. CS 672 3 Summer 2003 MPLS TE Components Label switching OSPF/ISISRSVP-TE RSVP control messages Data traffic IGP control messages

4. CS 672 4 Summer 2003 Tunnel Terminology R1 R3 R1 R2 R3 R4 R5R6 Tail Head Tunnel midpoint Tunnel is created at the head end

5. CS 672 5 Summer 2003 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. CS 672 6 Summer 2003 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. CS 672 7 Summer 2003 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. CS 672 8 Summer 2003 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. CS 672 9 Summer 2003 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. CS 672 10 Summer 2003 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. CS 672 11 Summer 2003 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. CS 672 12 Summer 2003 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”.