📚 node [[ospf]]
📓 garden/bbchase/networking/OSPF.md by @bbchase
  • Open Shortest Path First
  • References
  • [[Routing Protocol]]
    • #[[Link-state [[Routing Protocol]]]]
    • [[IGP]]
  • History
    • standardized in 1989
    • Developed largely by DEC
  • Terms
    • LSDB (Link State Database): A database that stores LSAs. This is how OSPF builds a picture of the network. A network topology map.
    • LSA (Link State Advertisement): A data structure that describes part of the network.
    • DBD or DDP (Database Description packet): A list of LSAs that a router has. This packet does not contain LSAs, just the headers. This is sent to a neighbor so it can figure out which LSAs to request.
    • LSU (Link State Update): A packet containing LSAs.
    • LSAck (Link State Acknowledgement): Confirms receipt of an LSU.
    • LSR (Link State Request): A packet which requests a list of LSAs that the router has found are missing or out of date based on its neighbor's Dababase Description (DBD).
    • Neighbors: A relationship between routers on the same data link that, once established, allows them to exchange their LSDBs.
  • OSPF Areas
    • 32-bit number, can be decimal or dotted-decimal
    • Area 0 (0.0.0.0)
      • Backbone area
      • All areas must connect to Area 0
    • Stub Area
    • Not-so-stubby Area (NSSA)
    • Totally Stubby Area
    • Totally Stubby NSSA
    • Transit Area
  • OSPF Router Types
    • IR (Internal Router)
    • BR (Backbone Router)
    • ABR (Area Border Router)
    • ASBR (Autonomous System Border Router)
  • OSPF Router Attributes
    • DR (Designated Router)
    • BDR (Backup Designated Router)
  • LSA Types
    • Type 1 - Router LSA
      • LSA Originator:: All routers
      • LSA Scope:: Same area
      • Advertises::
        • Itself
        • Links in the same area
    • Type 2 - Network LSA
      • LSA Originator:: DR
      • LSA Scope:: Same Area
      • Advertises::
        • Routers on the same segment
    • Type 3 - Summary LSA
      • LSA Originator:: ABR
      • LSA Scope:: Connected areas
      • Advertises::
        • Prefixes and metrics for connected area
        • Can optionally do route summarization
    • Type 4 - ASBR-Summary LSA
      • LSA Originator:: ABR
      • LSA Scope:: All except stub and NSSA
      • Advertises::
        • Location of ASBRs to other areas. ASBRs flood Type 1 LSA, which are not transmitted to other areas. When an ABR receives a Type 1 LSA form an ASBR, it creates a Type 4 LSA to send to other areas.
    • Type 5 - External LSA
      • LSA Originator:: ASBR
      • LSA Scope:: All except stub and NSSA
      • Advertises::
        • Information from other routing processes
    • Type 6 - Group Membership LSA
      • Meant for Multicast OSPF, Not widely used.
    • Type 7 - NSSA External LSA
      • LSA Originator:: ASBR in a NSSA
      • LSA Scope:: Same area
      • Advertises::
        • Mask for a Type 5 LSA in an area that blocks Type 5 LSAs. This is needed when an ASBR is inside a NSSA. When the Type 7 reaches the ABR, it's translated to a Type 5
    • Pick this up later: http://www.firewall.cx/networking-topics/routing/ospf-routing-protocol/1178-ospf-lsa-types-explained.html
    • Type 8 - External Attributes LSA
      • LSA Originator::
      • LSA Scope::
      • Advertises::
    • Type 9 - Link Scope Opaque LSA
      • LSA Originator::
      • LSA Scope::
      • Advertises::
    • Type 10 - Area Scope Opaque LSA
      • LSA Originator::
      • LSA Scope::
      • Advertises::
    • Type 11 - AS Scope Opaque LSA
      • LSA Originator::
      • LSA Scope::
      • Advertises::
  • Related
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