OSPF (Open Shortest Path First)

OSPF 

• It works on network layer as it is a layer three protocol.
• Its administrative distance(AD) is 110.
• Hope counts are unlimited.
• Works on IP protocol no. 89
• Multicast addressing 224.0.0.5, 224.0.0.6
• Denoted by "O" for same area route, "OIA" for different area route, "OE1/2" for redistributed routes.
• Authentication is plain text and MD5
• Manual summarization on ABR or ASBR
• Best path algorithm SPF (Shortest Path First)

—Autonomous System Boundary Router (ASBR) – They act as a gateway between two AS. The router which connects one AS to another or other routing protocol AS is called ASBR. Route redistribution is done on this router.

—Area Border Routers (ABRs) – These routers connect area 0 to the other area. It has at least one interface connected to area 0 and one or more interfaces to other areas. They propagate routes.

DR/BDR- Designated Routers/Backup Designated Router

   DR/BDR elections are based on RID- Router ID

   RID can be created 

1. Manually
2. The highest loopback IP address
3. The highest interface IP address

—OSPF network types:

• Broadcast(default on ethernet)
• Nonbroadcast (NBMA)
• Point to Point(default on Serial)
• Nonbroadcast Multiaccess