Loop-Free%20Alternates%20and%20Not-Via%20Addresses:%20A%20Proper%20Combination%20for%20IP%20Fast%20Reroute?

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Loop-Free Alternates and Not-Via AddressesA
Proper Combination for IP Fast Reroute?

• Rüdiger Martin, Michael Menth, Matthias Hartmann
• University of Wuerzburg
• Germany

Amund Kvalbein, Tarik Cicic Simula Research
Laboratories Norway
IETF 70, Vancouver, Canada RTGAREA Meeting
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Overview

• Qualitative comparison loop-free alternates
  (LFAs) vs. not-via addresses
• LFAs
• Taxonomy
• Appropriate usage for different protection levels
• Combined usage of LFAs and not-vias
• Availability of LFAs for different protection
  purposes
• Paths prolongation
• Decapsulation load from tunneled not-via traffic
• Conclusion

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LFAs and Not-Vias Qualitative Comparison
LFAs Not-Vias
Tunneling -
Backup path length (?) o (?)
Computational routing complexity o o
Failure coverage lt 100 100
Compatibility with loop-free re-convergence schemes o
Protection of multicast traffic -
Adaptability to SRLGs -
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Combined Use of LFAs and Not-Vias

• Not-vias
• Coverage of 100 single failures
• More elegant and powerful
• LFAs
• Readily available in todays routers
• No tunneling
• MTU issues
• Performance issues on old hardware
• Operators just dont like it
• Idea to achieve 100 failure coverage
• Use LFAs where possible
• Use not-vias where needed

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Classification of Neighbors wrt a Destination

• Neighbor nodes of router can be classified into
• Nodes protecting link and node failures
• ECAs
• Downstream LFAs
• Non-downstream LFAs
• Nodes protecting only link failures
• ECAs
• Downstream LFAs
• Non-downstream LFAs
• Nodes leading to loops when traffic is sent to (7)

All neighbors
General LFAs
Downstream LFAs
Equal-cost alternate
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LFAs and Not-Vias Combination Options

• Protection levels
• (i) Protection against all single link
  failures (1), (4), (2), (5), (3), (6), and
  not-via

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LFAs and Not-Vias Combination Options

• Protection levels
• (i) Protection against all single link
  failures (1), (4), (2), (5), (3), (6), and
  not-via
• (ii) Protection against all single link and all
  single node failures (1), (2), (3), and not-via
  (4), (5), and not-via for last link

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LFAs and Not-Vias Combination Options

• Protection levels
• (i) Protection against all single link
  failures (1), (4), (2), (5), (3), (6), and
  not-via
• (ii) Protection against all single link and all
  single node failures (1), (2), (3), and not-via
  (4), (5), and not-via for last link
• (iii) Protection against all single link and all
  single node failures with loop avoidance in the
  presence of multi-failures (1), (2), and
  not-via (4), (5), and not-via for last link

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Applicability of LFAs and Not-Vias
GEANT resilience requriement (i) only link
protection

• 0-80 not-vias required
• All ECAs link- node- protecting
• No other dwnstrm LFAs

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Applicability of LFAs and Not-Vias
GEANT resilience requriement (ii) link and node
protection

• 20-100 not-vias required

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Applicability of LFAs and Not-Vias
GEANT resilience requriement (iii) link, node
protection, loop avoidance for multi-flrs

• 20-100 not-vias required

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Path Prolongation
GEANT
(protection of link node flrs, loop avdnce for
mltflrs)
(protection of only link failures)
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Decapsulated Traffic from Not-Via Tunnels
GEANT
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Conclusion

• Classification of LFAs
• Combined usage of LFA and not-via to achieve 100
  failure coverage
• Applicability of LFA types depends on desired
  protection level
• Availability of applicable LFA types to protect a
  dest depends on
• Topology and position of node in the network
• Desired protection level
• Backup path length
• Longer with IPFRR than with IP reconvergence
• Small difference between combined usage and
  not-vias only
• Decapsulated traffic with combined usage and
  not-vias
• Less in many cases
• Maximum about the same
• Same link utilization for both mechanisms (not
  shown)
• LFAs attractive as a short-term solution