OSPF: open shortest part firstPoints to remember:

OSPF is open protocol & is link state protocol.

OSPF supports for VLSM & SUBNETTING.

OSPF uses Dijkstra Algorithm to calculate the best paths.

OSPF uses Cost (inverse of Bandwidth) as a metric.

Sends updates when topology changes.

OSPF is divided into hierarchical designs to minimize the routing

table.

It is divided in Areas & Autonomous System.

Hello packets mechanism is used as well as link state

advertisements packets are used to maintain the topology database.

OSPF supports load balancing of up to six equal-cost paths to a single

destination

OSPF intro.. Open Shortest Path First (OSPF) was developed by the Internet Engineering Task Force (IETF) as a replacement for the problematic RIP and is now the IETF-recommended Interior Gateway Protocol (IGP).

OSPF is a link-state protocol that, as the name implies, uses Dijkstra's Shortest Path First (SPF) algorithm and that is open that is, it isn't proprietary to any vendor or organization.

OSPF intro..The use of areas, which reduces the protocol's impact on CPU and memory, contains the flow of routing protocol traffic, and makes possible the construction of hierarchical network topologiesSupport of classless route table lookups, VLSM.Equal-cost load balancing for more efficient use of multiple paths More accurately, the RFC calls for equal-cost multipath, the discovery and use of multiple equal-cost paths, without prescribing how the protocol should route individual packets across these multiple paths. The Cisco OSPF implementation performs equal-cost load .The use of reserved multicast addresses to reduce the impact on non-OSPF speaking devices{224.0.0.5}.Support of authentication for more secure routing.The use of route tagging for the tracking of external routes.

OSPF: steps

OSPF tablesNeighbour table:

Also known as the adjacency database Contains list of recognized neighbors

Topology table: Typically referred to as LSDB Contains all routers and their attached links in the area or network. Identical LSDB for all routers within an area.

Routing table:Commonly named a forwarding database Contains list of best paths to destinations

OSPF terminologyLink :- an interface of a router which is connected or working and active for a particular network is called link.

LSA:- Link state Advertisement_ it is update that contain information about the state of link an ospf router will exchange LSA packet only with router with which it establish Adjacent.

Neighbor:- when reply to hello packet is received from a connected router that router is considered as a neighbor router.

Adjacency:- the direct relationship between the two OSPF routers that can interchange there information's updates router is very quick in sharing the routing updates than the other routing protocols.

But all the neighbors can never be the adjacent: it depends on the network type and configuration of the router

Hello protocol:- this protocol provide the dynamic neighbor discovery and maintain neighbor relationships hello packets And LSA`s are used to maintain the topology tableIt use multicast address {224.0.0.5}

OSPF terminologyROUTER ID: RID it is the IP address used to identify the router

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