CCNA 3 - Module 2This is a featured page



Single Area OSPF


Vocabulary - Key Terms:


IGP: Internet Gateway Protocol, Internet Protocol which distributes routing information to the routers.The term "gateway" is historical, "router" is currently the preferred term.

-Link-state routing Protocol:IGP. Remembers details of a complexed network topology. Requires each router to maintain at least a partial map of the network. When network topology changes, link state advertisements are spread throughout the network.

-Distance vector Protocol-an IGP that uses a distance calculation plus an outgoing network interface (a vector) to choose the best path to a destination network. Lest hop count.

-OSPF: Open Shortest Path First, OSPF is a link State protocol and is perhaps the most widely-used IGP in large enterprise networks



Related Articles:
Link State Vs. Distance Vector
Ciscos OSPF summary
Dijkstra's algorithm(ospf)

Key Concepts:

2.1.1 Review Of Link State Routing

Two main classes of IGPs are distance vector and link-state.

Examples of distance vector routing protocols in use today are RIP v2, IGRP, and the hybrid routing protocol EIGRP.

As networks become larger, limitations of DVA become apparent and Link-state protocols are in demand.

2.1.2 Link-state routing protocol features


Some Link State Routing Protocol Functions
  • Respond quickly to network changes
  • Send triggered updates only when a network change has occurred (link state advertisements) Send periodic updates known as link-state refreshes Use a hello mechanism to determine the reachability of neighbors


    2.1.3 How Routing Information Is Maintained

    Link-state routing protocols were designed to overcome the limitations of distance vector routing protocols.

    LSP is much more efficient at quickly detecting and coping with changes in network topology then DVP's due to efficiency of Link State Advertisements.

    2.1.4 Link State Routing Algorithms

    Every router remembers a part of the network topology, and whenever the topology changes a "link state advertisement" Is sent throughout the network.

    2.1.5 Advantages and Disadvantages of Link-State RoutingCCNA 3 - Module 2 - SMCROP - Cisco Networking
    2.1.6 Link State Vs. Distance Vector



    The benefits of link-state over distance vector protocols include faster convergence and improved bandwidth utilization.


    CCNA 3 - Module 2 - SMCROP - Cisco Networking

    2.2.1 OSPF Overview+ 2.2.2 Terminology

    -only supports tcp/ip protocol
    -OSPF preferred over rip because it is scaleable
    -OSPF passes on own and neighbors link state advertisements.
    -Each router keeps a list of adjacent neighbors, called the adjacency database.

    2.2.2 OSPF vs. Distance Vector

    Rip good for small networks because less hop count.
    OSPF is better for larger networks because it can determine the best path due to the speed of the link.

    2.2.5 OSPF network types

    OSPF interfaces automatically recognize three types of networks:
    • Broadcast multi-access, such as Ethernet
    • Point-to-point networks
    • Nonbroadcast multi-access (NBMA), such as Frame Relay

    2.2.6 OSPF Hello Protocol

    All routers periodically send out "hello messages" throughout the entire network to ensure that everything is running. Whereas link state routers only send out a similar "hello" message when there is a change in the network topology.
    Course Materials:

    CCNA 3 - Module 2 - Study Guide (.pdf)

    2.3.1 +2.3.2 Configuring OSPF

    CCNA 3 - Module 2 - SMCROP - Cisco Networking


    To enable OSPF routing, use the global configuration command syntax:
    Router(config)#router ospfprocess-id

    IP networks are advertised as follows in OSPF:
    Router(config-router)#network address wildcard-mask area area-id

    create and assign an IP address to a loopback interface use the following commands:
    Router(config)#interface loopback number
    Router(config-if)#ip address ip-address subnet-mask
    2.3.3 OSPF Cost Metric
    Every type of connection has a "cost" the less 1337 the connection, the higher the cost.

    2.3.4 Configuring OSPF Authentication (password)

    The password can be up to eight characters. Use the following command syntax to configure OSPF authentication:
    Router(config-if)#ip ospf authentication-keypassword

    After the password is configured, authentication must be enabled:
    Router(config-router)#areaarea-number authentication

    2.3.5 Configuring OSPF timers +2.3.6 Propogate route

    To configure the hello and dead intervals on an interface, use the following commands: CCNA 3 - Module 2 - SMCROP - Cisco Networking
    Router(config-if)#ip ospf hello-intervalseconds
    Router(config-if)#ip ospf dead-intervalseconds

    The following configuration statement will propagate this route to all the routers in a normal OSPF area:
    Router(config-router)#default-information originate

    2.3.7 Common Issues with OSPF
  • Hellos are not sent from both neighbors.
  • Hello and dead interval timers are not the same.
  • Interfaces are on different network types.
  • Authentication passwords or keys are different.
    •
    Media

    Link state routing protocol



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    Keyword tags: Distance Vector Protocol Link State Protocol open shortest path first OSPF
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