ospf-lite draft-thomas-hunter-reed-ospf-lite-00.txt Matthew Ramon Thomas [e-mail]

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ospf-litedraft-thomas-hunter-reed-ospf-lite-00.t
xtMatthew Ramon Thomasmrthom_at_essex.ac.uk
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ospf-lite features at a glance

• Branch version of OSPF (OSPFs baby brother)
• Avoids design phase.
• Instant on for customers with no configuration
  if required.
• Vendors can sell direct to client for large
  networks.
• Simple single area concept
• Support for external routes LSA 5s / Opaque LSAs
• The ability to boot up (2 stage) over non fully
  meshed multi-access network.
• MPLS core Service Providers can implement a
  simplified OSPF protocol on growing MPLS clouds
  without resorting to IS-IS.

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Method Overview 5 major Adaptations

• A single unified link type within the LSA 1 was
  introduced for all network types
• Hello protocol reworked to allow neighbor
  establishment over non fully meshed media
• A single LSA type is used to describe the router
• Designated router is no longer required
• Multiple instances solution to area LSA
  complexity

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A single link type for ospf-lite

• ospf-lite employs a single link type within the
  LSA 1
• ospf-lite treats all networks as ospf-lite-stub
  or ospf-lite-transit
• So its independent of the underlying network
  medium
• For NBMA networks ospf-lite still compensates
• Uses MIB IF lookup recognises NBMA interface
  and
• Additional 32 bit route still added for NBMA
  networks
• This is automatic
• OSPF P2MP P2P Broadcast NBMA types removed

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Promiscuous Hello Protocol

• Always on all networks treated the same.
• This allows ospf-lite to boot up over non fully
  meshed NBMA networks.

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Promiscuous Hello protocol cont..

• An ospf-lite router may see neighbors listed in
  another routers Hello.
• ospf-lite Hello then attempts a unicast Hello to
  connect to that neighbor.
• This may fail until routes are established
  between the directly communicating neighbors but
  the protocol remains promiscuous and establishes
  communication when the routes are in place.

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LSA type reduction

• All of the data required to build the calculation
  graph is carried inside the Router LSA 1.
• V2 has duplication in the LSA 2 due to the DR
  function
• ospf-lite has a single LSA type (Router LSA 1) to
  describe the router itself.
• External LSA 5s are supported
• Opaque LSA 91011 are supported

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DR Removal

• DR function originally designed for IS-IS with
  more active ES.
• ospf-lite removes all of the LSA 2s.
• Each LSA 2 is flooded throughout the whole area
  in OSPF V2
• If each router has an Ethernet then the number
  of LSA 2s could equal the number of router LSA
  1s
• The removal of these LSAs is a significant
  simplification

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Adjacencies on shared media are are now O(n2)

• This is by design.
• OSPF V2 avoids O(n2) but ospf-lite uses O(n2)
  when prudent

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O(n2) concerns linear

• With ospf-lite and V2 when routers are added to
  an internet
• LSA Traffic on an simple P2P internet does not
  increase O(n2) but increases linearly
• Adjacencies on an P2P internet do not increase
  O(n2)
• Each router generates its own LSAs
• These of course are copied by each router and
  distributed linearly
• LSA Traffic DOES increase as O(n2) on a broadcast
  or fully meshed network with no Designated Router
  function. Adjacencies also increase O(n2)
• What is n
• For n to become large the number or routers on an
  individual network would have to be large.
• A high number of nodes in a standard P2P cloud
  each on their own Ethernet connection equates to
  an n of 1
• Five routers sharing an Ethernet equates to an n
  of 5

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O(n2) concerns cont..

• Todays networks are largely point to point or
  have few routers on a single network / VLAN / PBT
  path so n is low.
• Ethernet comprises of multiple VLANS
• Frame clouds are often configured point-to-point

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Areas / Multiple instances

• Areas were originally conceived to summarize the
  database
• Although they can summarize routes this is
  normally achieved by manual configuration due to
  class addresses being split between areas.
• The areas do summarize the database.
• Video graphics programmers regularly run SPF on
  huge databases.
• Areas do succeed in shielding devices from routes

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Multiple Instances

• ospf-lite employs multiple instances with route
  redistribution where legacy areas are required.
• There is no theoretical limit to size of area.
• With multiple instances and redistribution there
  is no defined limit to AS size.
• BW utilisation is low so we are only limited by
  processor power and memory.

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IANA / WG Considerations

• We would like to use Version number zero
• This was never registered with IANA but its up to
  the Working Group to decide

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Thank you

• You know you could have half a cup of regular
  coffee but is it equal to a large skinny Latte