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Chapter (2)

Chapter (2). Single-Area OSPF. OSPF network types. A- Broadcast Multi-Access Network (BMA): - Broadcast multi-access is any LAN, such as Ethernet. B- Point-to-Point Network: - Point-to-Point is used where there is only one other router directly connected to the

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Chapter (2)

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  1. Chapter (2) Single-Area OSPF

  2. OSPF network types A- Broadcast Multi-Access Network (BMA): - Broadcast multi-access is any LAN, such as Ethernet. B- Point-to-Point Network: - Point-to-Point is used where there is only one other router directly connected to the transmitting or receiving router, such as a serial line

  3. OSPF network types C- Point-to-Multipoint Network: - Point-to-Multipoint is a single interface that connects to multiple destinations (configured be an administrator) - The network is treated as a series of point-to- point circuits D- Non-broadcast Multi-access Network (NBMA): - Non-broadcast multi-access network means a data link layer broadcast cannot be sent, such as Frame relay - OSPF sees it as a broadcast network

  4. OSPF Operation The basic process of learning routes for a router running OSPF for the first time: 1. The router discovers its neighbor on each interface. The list of neighbors is kept in a neighbor table 2. The router exchanges routing information with its neighbors using LSAs 3. The router places the received LSAs in its topology database (LSDB) 4. The router runs the SPF algorithm with the local router as the root to calculate the best routes to each subnet in the database 5. The router places the best route to each subnet in the routing table

  5. The Election of the DR - The DR is the router having the highest priority - If priorities were the same, the router having the highest RID is elected as the DR - The benefit of using the DR and BDR is to reduce the number of exchanges of routing information (LSAs)in networks with large number of neighbors - With BMA & NBMA networks, a DR and a BDR is elected - With Point-to-Point & Point-to-multipoint networks, OSPF has no need for a DR and a BDR

  6. The Hello packet The benefit of using hello packets: 1- Neighbor discovery: New OSPF routers send out hello packet with a multicast destination address (224.0.0.5) to all OSPF routers on the segment 2- Maintaining neighbor relationship: OSPF routers send hello packets periodically to ensure that their neighbors are still alive. If an OSPF router fails to hear a hello packet from its neighbor within a period of time, the OSPF router marks this neighbor as a dead router With point-to-point & BMA: hello packets are sent every 10 seconds, the hello dead interval is 40 seconds

  7. The Hello packet 3- Dynamic Election of the DR and BDR The hello packet contents

  8. The OSPF metric - The OSPF defines the metric of cost which is the inverse bandwidth. - Note: The default bandwidth of any serial line is 1544 kbps, if the line is a slower speed, use the bandwidth command to specify the real link speed

  9. OSPF Hierarchical design The benefit of using OSPF hierarchical design: 1- Reduction of routing overhead 2- Isolation of network instability to one area of the network 3- Speed up convergence

  10. Advantages & Disadvantages of Link State Routing protocols

  11. Overview of link state Routing

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