MPLS TE Application

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Lecture 11
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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

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MPLS TE Components
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Tunnel Terminology
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TE Headend Control

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

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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.

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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

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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.

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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)

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Tunnel Attributes

• Source IP address (headend)
• Destination IP address (tailend)
• Dynamicchoose the constraint-based shortest path
  first tunnel
• Staticuse the path specified
• Bandwidthtunnel capacity
• Priorityhigh-priority tunnels may preempt
  lower-priority tunnels
• Link coloringapply link attributes (affinity)

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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)

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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.