OSPF

           Open Shortest Path First           

1) Introduction-

-Allow routers to dynamically learn routes from other routers and to advertise routes to other routers.
-Keep track of the state of all network connection or links between itself and a network. 
-Link-State routing protocol.
-Most widely used 'Interior Gateway Protocol(IGP)'
-Operate within a single Autonomous System (AS).
-Transport IP, protocol type-89.
-Uses a Link-State routing algo. or shortest path first algo.
-Computes shortest path route using a method based on Dijkstra's  algo.
-Support VLSM/ Classless.

OSPF - Metric-

- Select the best path routes by finding the lowest cost path to a destination.
- All routers interface or links are given a cost
   - Based on bandwidth.
   - Can be set explicitly.

OSPF - Update destination address-

-Use 2 multicast address
    -224.0.0.5 (Sent to all SPF Router)
    -224.0.0.6 (Sent to all designated router)

OSPF - Areas-

-Uses areas to organize a network into hierarchical structure.
-Reduce the no of advertise routes.
-Reduce network load.


2.OSPF - Router ID-

-Unique identifier for each router.
-OSPF RID's are 32-bit numbers written in dotted decimal.
-Just like an Ip address.
-Using an Ip address is a convenient way to find a default RID.
-Alternatively the OSPF RID can be directly configured.
-By default RID is highest Ip address configured on any interface of router.
-Making loopback on router is best way to crate RID.