OSPF Routing Fundamentals
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Questions and Answers

What type of routers are F, G, and H?

  • Non-backbone internal routers (correct)
  • Backbone internal routers
  • Autonomous system boundary routers
  • Link-state routers

    • What route does the ABR router advertise to the non-backbone internal router?

  • A static route
  • A routing table
  • A dynamic route
  • A default route (correct)

    • What type of area can be configured in OSPF?

  • Stub area
  • Totally stubby area
  • Not-so-stubby area
  • All of the above (correct)

    • What is an ASBR?

    <p>Autonomous system boundary router</p> Signup and view all the answers

    What type of routing protocol maintains a complex database of the network topology?

    <p>Link-state protocol</p> Signup and view all the answers

    What is the purpose of link-state packets (LSPs)?

    <p>To construct a topological database using all received LSPs</p> Signup and view all the answers

    What triggers the LSP exchange in a network?

    <p>An event in the network</p> Signup and view all the answers

    What is the purpose of an SPF algorithm in link-state routing protocols?

    <p>To compute reachability to networked destinations</p> Signup and view all the answers

    What happens when a link-state router receives an LSA?

    <p>It updates its link-state database and forwards the LSA to all neighboring devices</p> Signup and view all the answers

    What can the process of link-state routing protocols discover?

    <p>Changes in the network topology caused by component failure or network growth</p> Signup and view all the answers

    What is the purpose of the link-state database?

    <p>To calculate the best paths through the network</p> Signup and view all the answers

    What is a link in the context of link-state routing?

    <p>An interface on a router</p> Signup and view all the answers

    Why are link-state protocols preferred in larger networks?

    <p>Because they support classless addressing and can be segmented into area hierarchies</p> Signup and view all the answers

    What algorithm is used by link-state routers to find the best paths to a destination?

    <p>Dijkstra's SPF algorithm</p> Signup and view all the answers

    What happens when a topology changes in a link-state routing protocol?

    <p>Routers always send updates when a topology changes</p> Signup and view all the answers

    What is a result of segmenting networks into area hierarchies?

    <p>Limited scope of route changes</p> Signup and view all the answers

    What is an advantage of link-state routing protocols over distance vector protocols?

    <p>More infrequent periodic refresh updates</p> Signup and view all the answers

    What is the purpose of the SPF tree?

    <p>To select the best paths for the routing table</p> Signup and view all the answers

    What is the advantage of using link-state routing protocol?

    <p>It allows the networked routers to converge faster</p> Signup and view all the answers

    What is the concern in Figure 4 when using link-state routing protocol?

    <p>There is no concern</p> Signup and view all the answers

    What is the purpose of metrics in link-state routing protocol?

    <p>To discriminate between different paths to the same destination</p> Signup and view all the answers

    Which router is the next hop for destination 185.134.0.0 from router A?

    <p>B</p> Signup and view all the answers

    What is the cost of the route from router A to destination 192.168.33.0?

    <p>1</p> Signup and view all the answers

    Which router is the next hop for destination 10.0.0.0 from router B?

    <p>A</p> Signup and view all the answers

    What is the cost of the route from router C to destination 185.134.0.0?

    <p>2</p> Signup and view all the answers

    Which router is the next hop for destination 192.168.157.0 from router C?

    <p>D</p> Signup and view all the answers

    What is the cost of the route from router D to destination 10.0.0.0?

    <p>2</p> Signup and view all the answers

    What is the advantage of using a link-state routing protocol in a network?

    <p>It allows for quicker convergence after a topological change</p> Signup and view all the answers

    What is the main difference between link-state routing protocols and distance vector protocols?

    <p>Link-state routing protocols use events to drive updates</p> Signup and view all the answers

    What is the benefit of using a link-state routing protocol in terms of bandwidth availability?

    <p>It makes more bandwidth available for routing traffic</p> Signup and view all the answers

    What type of networks is link-state routing best suited for?

    <p>Larger and more complex networks</p> Signup and view all the answers

    What is the metric used by the OSPF protocol?

    <p>Cost, which is equal to 100Mbps / BW in Mbps</p> Signup and view all the answers

    How are OSPF update messages sent?

    <p>As multicast messages</p> Signup and view all the answers

    How often does OSPF send LSA refresh update messages?

    <p>Every 30 minutes</p> Signup and view all the answers

    What is the Administrative Distance of the OSPF protocol?

    <p>110</p> Signup and view all the answers

    What feature does OSPF support?

    <p>Manual summarization</p> Signup and view all the answers

    What do link-state protocols use to choose paths through the network?

    <p>Cost metrics</p> Signup and view all the answers

    What happens when a link-state routing protocol detects a change in the network topology?

    <p>It begins forwarding packets through an alternate path</p> Signup and view all the answers

    What is a benefit of link-state protocols over traditional distance vector algorithms?

    <p>They can immediately report changes in the network topology</p> Signup and view all the answers

    Why is it difficult for routing loops to occur in link-state protocols?

    <p>Because each router has a complete and synchronized picture of the network</p> Signup and view all the answers

    What is a benefit of sequencing and aging LSPs?

    <p>Routers can base their routing decisions on the latest set of information</p> Signup and view all the answers

    What is a characteristic of link-state routing protocols during initial topology discovery?

    <p>They flood the network with LSPs</p> Signup and view all the answers

    What is a result of careful network design in link-state protocols?

    <p>Smaller link-state database sizes</p> Signup and view all the answers

    What is the main advantage of using triggered, flooded updates in link-state protocols?

    <p>Immediate reporting of changes in the network topology</p> Signup and view all the answers

    What is the main application of link-state routing protocols?

    <p>Networks of any size</p> Signup and view all the answers

    Study Notes

    • Each link-state router takes a copy of the LSA, updates its link-state database, and forwards the LSA to all neighboring devices.
    • LSAs cause every router within the area to recalculate routes, so it's recommended to limit the number of link-state routers in an area.
    • A link is similar to an interface on a router, and the state of the link is a description of that interface and its relationship to its neighboring routers.
    • Link-state protocols always send updates when a topology changes.
    • Periodic refresh updates are more infrequent than for distance vector protocols.
    • Networks running link-state routing protocols can be segmented into area hierarchies, limiting the scope of route changes.
    • Networks running link-state routing protocols support classless addressing.

    Non-Backbone Internal Routers

    • Non-backbone internal routers are aware of the topology within their respective areas and maintain identical link-state databases about the areas.
    • The ABR router will advertise a default route to the non-backbone internal router.
    • The internal router will use the default route to forward all inter-area or interdomain traffic to the ABR router.
    • Link-state routing algorithms, known as SPF protocols, maintain a complex database of the network topology.
    • Each router that has exchanged LSPs constructs a topological database using all received LSPs.
    • An SPF algorithm is then used to compute reachability to networked destinations.
    • This information is employed to update the routing table.
    • Link-state protocols use cost metrics to choose paths through the network.
    • By using triggered, flooded updates, link-state protocols can immediately report changes in the network topology to all routers in the network.
    • Because each router has a complete and synchronized picture of the network, it is difficult for routing loops to occur.
    • Because LSPs are sequenced and aged, routers always base their routing decisions on the latest set of information.
    • With careful network design, the link-state database sizes can be minimized, leading to smaller SPF calculations and faster convergence.

    Features of OSPF Protocol

    • OSPF is an open standard protocol supported by many vendors.
    • OSPF can run many instances in parallel.
    • The metric used by OSPF is called Cost, which is equal to 100Mbps / BW in Mbps.
    • OSPF update messages are triggered and incremental updates are sent as multicast messages using the addresses 224.0.0.5 & 224.0.0.6.
    • OSPF periodically sends LSA refresh update messages every 30 minutes.
    • OSPF update messages are called as LSU - Link State Update, which may contain many LSAs - Link State Advertisement.
    • There are as many as 11 types of LSUs in OSPF.
    • The Administrative Distance of OSPF protocol is 110.
    • OSPF protocol supports manual summarization and VLSM.
    • Route announcements carry subnet mask.

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    Related Documents

    ch6.pdf

    Description

    Learn about OSPF routing and its router types. Identify the type of routers F, G, and H, and understand how ABR routers advertise routes to non-backbone internal routers.

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