CS 672
Summer 2003
Lecture 11
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CS 672
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
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CS 672
Summer 2003
MPLS TE Components
IGP control messages
RSVP control messages
OSPF/ISIS
Data traffic
RSVP-TE
Label switching
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CS 672
Summer 2003
Tunnel Terminology
Tunnel is created at
the head end
R3
R2
R1
Tunnel
R5
R6
R1
R4
R3
Head
midpoint
midpoint
Tail
midpoint
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CS 672
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)
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CS 672
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.
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CS 672
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
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CS 672
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.
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CS 672
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)
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CS 672
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)
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CS 672
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)
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CS 672
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 “makebefore-break”.
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