Sina Mirtorabi ( sina @ cisco.com)

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Sina Mirtorabi ( sina _at_ cisco.com)
Tunnel Adjacency
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Agenda

• What is Tunnel Adjacency ( TA ) ?
• What does TA resolve ?
• Scenarios where TA is used
• How is TA established ?
• How data packet are forwarded ?
• TA configuration parameter

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What is Tunnel Adjacency ?

• TA is a new proposal in order to solve intra-area
  / Inter-area path preference
• It is basically a generalization of VL
• It can force OSPF to take a desired path
• It has on-demand area partition repair

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What does TA resolve ?

• Intra-area / Inter-area path preference
• In HS topology, it save the cost of adding
  additional interface between ABRs.
• On demand partition repair to avoid segmented
  area, required when summarization is done.

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Scenarios where TA is used ( sub-optimum path)
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Scenarios where TA is used ( sub-optimum path)
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Scenarios where TA is used ( sharing link for
different areas )
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How is TA established ?

• As for VL, TA is configured between two ABRs
  having in common an area
• when there is an intra-area path through transit
  area, the adjacency is established and announced
  in the area for which the TA is configured.

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How data packet is forwarded ?

• If ABRs have a direct link, data packet are sent
  without any encapsulation
• If ABRs are multi-hop, data packet are
  encapsulated
• Encapsulation is dynamic and user does not need
  to configure

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TA configuration parameter

• TA configuration parameter consists of
• - remote neighbor Router-ID
• - TA Transit Area ( TTA )
• - The Area to which TA belongs
• Optionally, encapsulation type and on demand
  partition repair

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To Summarize

• TA is a generalization of VL
• It resolves VL limitations
• - TA link can belong to any area
  - Summarization is not affected
  - TA can go through Stub/NSSA
• It has added value features
• - TA cost is configurable
  
• - TA on demand partition repair
• - Multiple TA through a given path
  

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THANK YOU