Open Shortest Path First --- OSPF

                                                     OSPF in a Nutshell

• Open standard link state
• Operates on IP Port 89
• Dynamic neighbor discovery
• Sends Hellos to OSPF speaking routers via a Multicast address of 224.0.0.5
• If a Designated Router (DR) exists, non-DR routers exchange messages with the DR via 224.0.0.6
• Utilizes the Dijkstra algorithm, a shortest path first, to ensure loopfree delivery
• Hello timers are 10 seconds, dead interval is 40 seconds for broadcast and point-to-point networks (30/120 on everything else)
• Administrative distance (AD) is 110
• Unlike EIGRP, OSPF does not share topology tables, it maintains the local link state database by flooding and receiving LSAs
• OSPF must be configured into an area and must match the neighbor
• OSPF area 0 is the backbone area
• All other OSPF areas communicate through Area Border Routers (ABR) connected to the backbone area 0