OSPF over NBMA: Five Modes

Non-Broadcast (NBMA) – RFC Standard

  • Default mode for X25, FR ARM
  • Neighbors statically configured
  • All WAN interfaces must all be in same subnet.
  • Acts like LAN environment
  • DR/BDR elected (DR/BDR must have FULL connectivity to all neighbors i.e. hub must be DR in a hub and spoke style network)

Point-to-Multipoint – RFC Standard

  • Fixes issues with NBMA networks – treats cloud like series of P2P links.
  • Requires Single Subnet
  • No DR/BDR Elected
  • Neighbors automatically form (as long as pseudo-broadcasts are enabled*

* frame-relay map x.x.x.x dlci broadcast

Point-to-Point – Cisco Proprietary (normal WAN Point to point style behavior on NBMA)

  • Uses seperate sub-interfaces.
  • Requires different subnets
  • No DR/BDR Elected
  • Requires different subnets
  • Neighbors automatically form

Broadcast – Cisco Proprietary (Ethernet style behavior on NBMA network)

Point to Multipoint, Non-Broadcast – Cisco Proprietary.

  • Fixes issues with NBMA networks
  • Requires Single Subnet
  • No DR/BDR Elected
  • Neighbors do not automatically form
  • Might be used where routers do not support pseudo broadcasts

 

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