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seconds. It computes the shortest path tree for each route using a method based on Dijkstra's algorithm, a shortest
path first algorithm. OSPF detects changes in the topology, such as link failures, and The OSPF routing policies for
constructing a route table are governed by link cost factors (external metrics) associated with each routing interface.
Cost factors may be the distance of a router (round-trip time), data throughput of a link, or link availability and
reliability, expressed as simple unitless numbers. This provides a dynamic process of traffic load balancing between
routes of equal cost.
The OSPF routing policies for constructing a route table are governed by link cost factors (external metrics) associated
with each routing interface. Cost factors may be the distance of a router (round-trip time), data throughput of a link, or
link availability and reliability, expressed as simple unitless numbers. This provides a dynamic process of traffic load
balancing between routes of equal cost.
An OSPF network may be structured, or subdivided, into routing areas to simplify administration and optimize traffic
and resource utilization. Areas are identified by 32-bit numbers, expressed either simply in decimal, or often in
octet-based dot-decimal notation, familiar from IPv4 address notation.
An OSPF network may be structured, or subdivided, into routing areas to simplify administration and optimize traffic
and resource utilization. Areas are identified by 32-bit numbers, expressed either simply in decimal, or often in
octet-based By convention, area 0 (zero), or 0.0.0.0, represents the core or backbone area of an OSPF network. The
identifications of other areas may be chosen at will; often, administrators select the IP address of a main router in an
area as area identification. Each additional area must have a direct or virtual connection to the OSPF backbone area.
Such connections are maintained by an interconnecting router, known as area border router (ABR). An ABR maintains
separate link state databases for each area it serves and maintains summarized routes for all areas in the network.By
convention, area 0 (zero), or 0.0.0.0, represents the core or backbone area of an OSPF network. The identifications of
other areas may be chosen at will; often, administrators select the IP address of a main router in an area as area
identification. Each additional area must have a direct or virtual connection to the OSPF backbone area. Such
connections are maintained by an interconnecting router, known as area border router (ABR). An ABR maintains
separate link state databases for each area it serves and maintains summarized routes for all areas in the network.
OSPF does not use a TCP/IP transport protocol, such as UDP or TCP, but encapsulates its data in IP datagrams with
protocol number 89. This is in contrast to other routing protocols, such as the OSPF does not use a TCP/IP transport
protocol, such as UDP or TCP, but encapsulates its data in IP datagrams with protocol number 89. This is in contrast to
other routing protocols, such as the Routing Information Protocol (RIP) and the Border Gateway Protocol (BGP). OSPF
implements its own error detection and correction functions.
-Protocol messages
Unlike other routing protocols, OSPF does not carry data via a transport protocol, such as the User Datagram Protocol
(UDP) or the Transmission Control Protocol (TCP). Instead, OSPF forms IP datagrams directly, packaging them using
protocol number 89 for the IP Protocol field. OSPF defines five different message types, for various types of
communication:
