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    OSPF

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    supermonkey21
    OSPF is a link-state routing protocol that offers faster convergence and scales to larger networks than RIP. It uses areas and link-state information to build adjacency, link-state, and forwarding databases using messages exchanged between routers. The databases are used by the Dijkstra shortest path first algorithm to calculate the best routes and populate the routing tables.

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    OSPF

    Uploaded by

    supermonkey21
    21 views2 pages
    OSPF is a link-state routing protocol that offers faster convergence and scales to larger networks than RIP. It uses areas and link-state information to build adjacency, link-state, and forwarding databases using messages exchanged between routers. The databases are used by the Dijkstra shortest path first algorithm to calculate the best routes and populate the routing tables.

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    OSPF is a link-state routing protocol that offers faster convergence and scales to larger networks than RIP. It uses areas and link-state information to build adjacency, link-state, and forwarding databases using messages exchanged between routers. The databases are used by the Dijkstra shortest path first algorithm to calculate the best routes and populate the routing tables.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    21 views2 pages

    OSPF

    Uploaded by

    supermonkey21
    OSPF is a link-state routing protocol that offers faster convergence and scales to larger networks than RIP. It uses areas and link-state information to build adjacency, link-state, and forwarding databases using messages exchanged between routers. The databases are used by the Dijkstra shortest path first algorithm to calculate the best routes and populate the routing tables.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 2

    OSPF – Open Shortest Path First

    OSPF is a link-state routing protocol that was developed as an alternative for the distance vector
    Routing Information Protocol (RIP). OSPF has significant advantages over RIP in that it offers faster
    convergence and scales to much larger network implementations.

    OSPF is a link-state routing protocol that uses the concept of areas.

    A network administrator can divide the routing domain into distinct areas that help control
    routing update traffic.

    A link is an interface on a router. A link is also a network segment that connects two routers, or a
    stub network such as an Ethernet LAN that is connected to a single router. Information about the
    state of a link is known as a link-state. All link-state information includes the network prefix, prefix
    length, and cost

    COMPONENTS OF OSPF
    All routing protocols share similar components. They all use routing protocol messages to
    exchange route information. The messages help build data structures, which are then processed
    using a routing algorithm.

    Routing Protocol Messages


    Routers running OSPF exchange messages to convey routing information using five types of
    packets.

    • Hello packet
    • Database description packet
    • Link-state request packet
    • Link-state update packet
    • Link-state acknowledgment packet

    These packets are used to discover neighboring routers and to exchange routing information to
    maintain accurate information about the network.

    Data Structures
    OSPF messages are used to create and maintain three OSPF databases, as follows:

    Adjacency database - This creates the neighbor table.


    Link-state database (LSDB) - This creates the topology table.
    Forwarding database - This creates the routing table.
    These tables contain a disc neighboring router to exchange routing information. The tables are kept
    and maintained in RAM.

    Database Table Description


    Adjacency Neighbor - List of all neighbor routers to which a router has established bidirectional
    communication.
    - This table is unique for each router.
    - Can be viewed using the show ip ospf neighbor command.
    Link-state Topology - Lists information about all other routers in the network.
    - This database represents the network topology.
    - All routers within an area have identical LSDB.
    - Can be viewed using the show ip ospf database command.
    Forwarding Routing - List of routes generated when an algorithm is run on the link-state database.
    - The routing table of each router is unique and contains information on how
    and where to send packets to other routers.
    - Can be viewed using the show ip route command.

    Algorithm
    The router builds the topology table using results of calculations based on the Dijkstra shortest
    path first (SPF) algorithm. The SPF algorithm is based on the cumulative cost to reach a
    destination.

    The SPF algorithm creates an SPF tree by placing each router at the root of the tree and
    calculating the shortest path to each node. The SPF tree is then used to calculate the best routes.
    OSPF places the best routes into the forwarding database, which is used to make the routing table.

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