CCNA3_M2_Single_Area_OSPF (1130756), страница 2

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A router with thesecond highest priority will be the BDR.• When OSPF priorities are the same, the OSPF electionfor DR is decided on the router ID. The highest router IDis selected.• After the election process, the DR and BDR retain theirroles even if routers are added to the network withhigher OSPF priority values.Router Priority• If the network type of an interface is broadcast, thedefault OSPF priority is 1.• The priorities can be set to any value from 0 to 255.• Modify the OSPF priority by entering interfaceconfiguration:Router(config-if)#ip ospf priority number• To verify OSPF interface priority:Router#show ip ospf interface type numberShow ip ospf interfaceModifying OSPF cost metric• Cost is calculated using the formula 10^8/bandwidth,where bandwidth is expressed in bps.• It is essential for proper OSPF operation that the correctinterface bandwidth is set.Router(config)#interface serial 0/0Router(config-if)#bandwidth 64• The cost number can be between 1 and 65,535.• Use the following interface configuration command toset the link cost:Router(config-if)#ip ospf cost numberCisco IOS Default IOS Path CostConfiguring OSPF authentication• The password can be up to eight characters.Use the following command syntax to configureOSPF authentication:Router(config-if)#ip ospf authentication-key password• After the password is configured, authenticationmust be enabled:Router(config-router)#area area-number authenticationEncrypted authentication• With simple authentication, the password is sent asplain text.

This means that it can be easily decoded if apacket sniffer captures an OSPF packet.• To send encrypted authentication information and toensure greater security, the message-digest keyword isused.• The MD5 keyword specifies the type of message-digesthashing algorithm to use, and the encryption type fieldrefers to the type of encryption, where 0 means noneand 7 means proprietary.Configure encrypted authentication• To send encrypted authentication information and toensure greater security, the message-digest keyword isused.• Use the interface configuration command mode syntax:Router(config-if)#ip ospf message-digest-key key-id md5encryption-type key• The key-id is an identifier and takes the value in therange of 1 through 255. Neighbor routers must use thesame key identifier with the same key value.• The following is configured in router configurationmode:Router(config-router)#area area-id authenticationmessage-digestConfiguring OSPF timers• OSPF routers must have the same hello intervals andthe same dead intervals to exchange information.• By default, the dead interval is four times the value ofthe hello interval.• On broadcast OSPF networks, the default hello intervalis 10 seconds and the default dead interval is 40seconds.• On nonbroadcast networks, the default hello interval is30 seconds and the default dead interval is 120 seconds.Configuring OSPF timers• The default values result in efficient OSPFoperation and seldom need to be modifiedunless to improve performance.• To configure the hello and dead intervals on aninterface, use the following commands:Router(config-if)#ip ospf hello-interval secondsRouter(config-if)#ip ospf dead-interval secondsOSPF, propagating a default route• The following configuration statement willpropagate the default route to all the routers in anormal OSPF area:Router(config-router)#default-information originatePropagating a default routeCommon OSPF configuration issues• Failure to establish a neighbor relationship is caused byany of the following reasons:––––––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 differentRouter neighbors have duplicate IP addressesRouter interfaces have not been upVerifying the OSPF configurationDebug and clear commandsSummary•••••••The features of link-state routingOSPF terminologyOSPF network typesThe OSPF Hello protocolThe basics steps in the operation of OSPFOSPF configurationOSPF verificationLab Topology10 ip30 ip60 ip30 ip10 ipCCNA3 – Module2•••••••60 ip199.6.3.0/24ProcessID: 5DR:Branch1 & Site2Key:newospfHello: 17sDead: 49sInternet:Branch1Loopback.

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