Module 3 - OSPF Network Types pot

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BSCI Module 3 Lesson 4 - OSPF Network Types

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Objective

 OSPF Network Types

 Adjacency Behavior for a Point-to-Point Link

 Adjacency Behavior for a Broadcast Link

 Selecting the DR and BDR

 Adjacency Behavior for a NBMA Network

 DR Election in NBMA Topology

 OSPF Over Frame Relay

 OSPF over NBMA Topology Modes

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Different Network Types and OSPF

 There are three distinct classifications of physical network media that

OSPF can differentiate between Each of these network types requires a slightly different configuration to optimize the performance of OSPF

 Cisco IOS Software allows five main network types to be configured, as

displayed in Table 5-5

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OSPF Network Types

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Configuring the Network Type

 OSPF is highly adaptable Consider its capability to accommodate either

broadcast or nonbroadcast multiaccess (NBMA) network types OSPF responds accordingly by altering its operation to reflect the configuration that you have given it

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 When this command is applied to an interface, OSPF elects a DR/BDR,

builds an adjacency with the DR, and builds neighbor relationships with all other OSPF routers in the network

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Nonbroadcast Networks

 When configuring an interface as nonbroadcast, OSPF cannot perform

multicasting on that link

 Lack of multicast functionality impacts OSPF’s operation because OSPF

Hellos cannot be properly transmitted

 Physical Frame Relay interfaces and multipoint subinterfaces are

recognized as nonbroadcast by default The following alternatives allow you to make OSPF operate when a nonbroadcast type network is

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Học viện mạng Bách Khoa - www.bkacad.comNonbroadcast Networks

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Point-to-Multipoint Networks

 OSPF point-to-multipoint interfaces are defined as numbered

point-to-point subinterfaces, with the router having one or more OSPF neighbors

 An OSPF point-to-multipoint network has the following benefits compared

to nonbroadcast multiaccess and point-to-point networks:

–Point-to-multipoint is easier to configure because it requires no configuration of neighbor commands Point-to-multipoint

connections consume only one IP subnet and require no designated router election process

– Point-to-multipoint has a fully or partial meshed topology.

– Point-to-multipoint can be more reliable in fully meshed networks because it maintains connectivity in case of virtual circuit failure.

–When you configure the OSPF network type as multipoint , routing between two routers not directly connected goes through the router (hub) that has virtual circuits to both routers (spokes).

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Học viện mạng Bách Khoa - www.bkacad.comPoint-to-Multipoint Networks

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Point-to-Point Networks

 When you configure an interface as an OSPF point-to-point network type,

this command understands that the only other OSPF-speaking router on that interface is directly connected

 As previously mentioned, the following methods can be used to get OSPF

to operate in such a configuration:

–Use point-to-point subinterfaces

–Use a physical interface and an OSPF point-to-point network type

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Adjacency Behavior for a Point-to-Point Link

 Hello time 10s, Dead time 40

 Neighboring routers become adjacent whenever they

can communicate directly

 Usually, the IP source address of an OSPF packet is

set to the address of the outgoing interface on the router

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Adjacency Behavior for a Broadcast Link

 Reduce routing update traffic

 Manage link-state synchronization

 Note:

After a DR and BDR have been selected, any router added to the

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Selecting the DR and BDR

 It is more efficient to have one router represent the

other routers to a new router rather than all the routers pass the same information

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Setting Priority for DR election

 The BDR uses the wait timer to determine whether the

DR is out of service

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Adjacency Behavior for a NBMA Network

 If the NBMA topology is not fully meshed, a broadcast

or multicast sent by one router will not reach all the other routers.

 To implement broadcasting or multicasting router

replicates the packets sends them individually on each permanent virtual circuit (PVC)

Hello Time 30s; Dead Time 120s

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DR Election in NBMA Topology

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OSPF Over Frame Relay

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OSPF over NBMA Topology Modes of

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Activity

 3.4.1 Drag and Drop: OSPF Network Types

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

 3.4.4 Checkbox: DR and BDR Election

– Upon completion of this activity, the student will be able to identify the process of DR and BDR election.

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Q and A

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