Module 3 - Review of OSPF Operation potx

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BSCI Module 3 Lesson 2 - Review of OSPF Operation

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 OSPF Packet Types

 OSPF Packet Header Format

 Establishing OSPF Neighbor Adjacencies

 Exchanging and Synchronizing LSDBs

 Discovering the Network Routes

 Maintaining Network Routes

 Maintaining Link-State Sequence Numbers

 Verifying Packet Flow

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OSPF Packet Formats

 All OSPF packets begin with a 24-octet header

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OSPF Packet Types

 Version is the OSPF version number.

 Type specifies the packet type following the header.

 Packet length is the length of the OSPF packet, in octets, including the

header.

 Router ID is the ID of the originating router.

 Area ID is the area from which the packet originated.

 AuType is the authentication mode being used.

 Authentication is the information necessary for the packet to be

authenticated by whatever mode is specified in the AuType field.

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OSPF Packet Types

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OSPF Packet Header Format

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The Hello Packet

 The Hello packet establishes and maintains adjacencies The Hello carries

parameters on which neighbors must agree in order to form an adjacency.

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The Database Description Packet

 The Database Description packet is used when an adjacency is being

established (see "Building an Adjacency," earlier in this chapter) The primary purpose of the DD packet is to describe some or all of the LSAs in the originator's database so that the receiver can determine whether it has

a matching LSA in its own database This is done by listing only the headers of the LSAs.

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The Link State Request Packet

 As Database Description packets are received during the database

synchronization process, a router will take note of any listed LSAs that are not in its database or are more recent than its own LSA These LSAs are recorded in the Link State Request list The router will then send one or more Link State Request packets asking the neighbor for its copy of the LSA.

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The Link State Update Packet

 The Link State Update packet, is used in the flooding of LSAs and to send

LSAs in response to Link State Requests.

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The Link State Acknowledgment Packet

 Link State Acknowledgment packets are used to make the flooding of

LSAs reliable Each LSA received by a router from a neighbor must be explicitly acknowledged in a Link State Acknowledgment packet.

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Establishing OSPF Neighbor Adjacencies

Highest IP loopback then physical 10S&40s or 30s&120s RID of neighbor

Area 0 or Area # 0

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Elect DR/BDR

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Link-State Database Synchronization

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Exchanging and Synchronizing LSDBs

On nonbroadcast multiaccess

(NBMA), point-to-multipoint, and virtual links , the hello packets are sent in unicast packets

Note

After a DR and BDR are selected, any router added to the network establishes adjacencies with the

DR and BDR only.

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Discovering the Network Routes

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Maintaining Network Routers

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Maintaining Link-State Sequence Numbers

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Verifying Packet Flow

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 3.2.1 Drag and Drop: OSPF Packet Types

– Upon completion of this activity, the student will be able to identify the different OSPF packet types.

 3.2.2 Drag and Drop: OSPF Packet Header

– Upon completion of this activity, the student will be able to identify the different fields in an OSPF packet header.

 3.2.5 Drag and Drop: OSPF States

– Upon completion of this activity, the student will be able to list

in order the different states of OSPF.

 3.2.5 Drag and Drop: OSPF Neighbor States

– Upon completion of this activity, the student will be able to identify the different OSPF neighbor states.

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Self Check

1 List 5 types of OSPF packets

2 Which router will be Master

3 Meaning of Sequence Number for LSA

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 OSPF Packet Types

 OSPF Packet Header Format

 Establishing OSPF Neighbor Adjacencies

 Exchanging and Synchronizing LSDBs

 Discovering the Network Routes

 Maintaining Network Routes

 Maintaining Link-State Sequence Numbers

 Verifying Packet Flow

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Q and A

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