OSPF Database Exchange Summary List Optimization draft-ietf-ospf-dbex-opt-00.txt

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OSPF Database ExchangeSummary List
Optimizationdraft-ietf-ospf-dbex-opt-00.txt
IETF 68 - OSPF WG

• Richard Ogier
• Presented by Acee Lindem
• March 19, 2007

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Database Exchange Optimization

• Basic idea Router does not need to list an LSA
  in a Database Description (DD) packet if the
  neighbor already has the same instance or a newer
  instance of the LSA.
• Reason The neighbor will not request the LSA
  from the router.
• Mechanism When the router accepts a received DD
  packet as the next in sequence from a neighbor in
  state Exchange, the following additional step is
  performed for each LSA listed in the packet
• If the Database summary list for the neighbor
  contains an instance of the LSA that is the same
  or less recent than the one listed in the packet,
  the LSA is removed from the Database summary list.

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Benefits of Optimization

• Fully backward compatible with OSPFv2 and OSPFv3.
• Does not affect synchronization, since the LSAs
  omitted from DD packets are unnecessary.
• Reduces the overhead of DD packets by about 50
  in large networks.
• Reason It reduces the number of LSA headers
  exchanged by about 50 when the two routers are
  already nearly synchronized (see example).
• Especially useful in MANETs, in which an
  adjacency is often formed between two routers
  that are already nearly synchronized.

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Changes since IETF 66

• Draft clarifies that the additional step must be
  performed for every LSA listed in the received DD
  packet (to fully update the summary list) before
  the next DD packet is sent in response.
• For faster lookup of LSAs in the summary list,
  the draft suggests that LSAs be listed in
  lexicographically increasing order of(LS type,
  Link State ID, Advertising Router) for OSPFv2
  and(LS type, Advertising Router, Link State ID)
  for OSPFv3.