CCNA3_M2_Single_Area_OSPF (1130756)
Текст из файла
CCNA – Semester3Module 2Single Area OSPFObjectives• Link State Routing Protocol• Single Area OSPF Concepts• Single Area OSPF ConfigurationLink State Routing ProtocolLink State and Distance Vector RoutingLink-state routing protocol• Collect routing information from all otherrouters in the network or within a defined areaof the network.• Each router independently calculates its bestpaths to all destinations in the network.• It is less likely to propagate incorrectinformation provided by any of its neighboringroutersLink-state routing protocol functions• Link-state routing protocols perform thefollowing functions:– Respond quickly to network changes– Send triggered updates only when a network change hasoccurred– Send periodic updates known as link-state refreshes– Use a hello mechanism to determine the reachability ofneighborsLink State RoutingLink-state routing concepts• Link-state routing uses thefollowing features:– Link-state advertisements (LSAs)– A topological database– The shortest path first (SPF)algorithm– The resulting SPF tree– A routing table of paths and portsto each network to determine thebest paths for packetsAdvantages of link-state routing••••Fast convergenceUse cost metricNo routing loopThe awareness of the entire network greatly assisttroubleshooting.• Support CIDR and VLSMDisadvantages of link-state routing• Require more memory and processing power thandistance vector routers.• Require strict hierarchical network design.• They require good understanding of link-state routing.• Initial discovery process by flooding LSAs cansignificantly decrease the capability of the network totransport data.Single Area OSPF ConceptsSingle Area OSPF• Open Shortest Path First(OSPF) is a link-staterouting protocol based onopen standards.• OSPF proves to be arobust and scalablerouting protocol.• OSPF can be used andconfigured as a singlearea for small networks.Large OSPF network•••Large OSPF networks use a hierarchical design.Multiple areas connect to a distribution area, area 0, also called thebackbone.Defining areas reduces routing overhead, speeds up convergence,confines network instability to an area and improves performance.OSPF terminologyOSPF terminologyOSPF terminologyOSPF terminologyOSPF terminologyOSPF terminologyOSPF terminologyOSPF terminologyProblem: Link state UpdatesOSPF Features• OSPF addresses the following issues:–––––Speed of convergenceSupport for Variable Length Subnet Mask (VLSM)Network sizePath selectionGrouping of membersShortest path algorithm•••Each node has a complete database of all the links so completeinformation about the physical topology is known.All router link-state databases are identical.The shortest path algorithm then calculates a loop-free topologyNeighbor Relationship• A neighbor relationship is required for OSPF routers toshare routing information.• A router will try to become adjacent, or neighbor, to atleast one other router on each IP network to which it isconnected.• OSPF routers determine which routers to becomeadjacent to based on the type of network they areconnected to.
Once an adjacency is formed betweenneighbors, link-state information is exchanged.OSPF network types••A neighbor relationship,adjacent, is required for OSPFrouters to share routinginformation which depends onnetwork type.OSPF interfaces recognizethree types of networks:– Broadcast multi-access, such asEthernet– Point-to-point networks– Nonbroadcast multi-access(NBMA), such as Frame Relay•A fourth type, point-tomultipoint, can be configuredon an interface by anadministrator.OSPF: Adjacency• Too much overhead if n routers, n*(n-1)/2adjacencies need to be formed.• The solution to this overhead is to hold anelection for a designated router (DR).• All routers in a network form adjacency with DRand BDR (backup designated router).• Link-state information sent to OSDF routers(DROther) at 224.0.0.5.• DROther sent link-state information to DR andBDR at 224.0.0.6OSPF Network Type• On point-to-point networks only two nodes exist and noDR or BDR is elected.
Both routers become fullyadjacent with each other.DR and BDR Receive RSAsOSPF Hello protocol• The hello packets are addressed to the multicastaddress 224.0.0.5.• OSPF routers use hello packets to initiate newadjacencies and to ensure that neighbor routersare still functioning.• Hellos are sent every 10 seconds by default onbroadcast multi-access and point-to-pointnetworks.• On interfaces that connect to NBMA networks,such as Frame Relay, the default time is 30seconds.OPSF Packet Header• On multi-access networks the Hello protocol elects adesignated router (DR) and a backup designated router(BDR).OSPF Hello HeaderExchange ProcessA172.16.5.1/24E0172.16.5.2/24E1BDown StateExchange ProcessA172.16.5.1/24E0172.16.5.2/24E1BDown StateI am router ID 172.16.5.1 and I see no one.Init StateRouter BNeighbors List172.16.5.1/24, int E1Exchange ProcessA172.16.5.1/24E0172.16.5.2/24E1BDown StateI am router ID 172.16.5.1 and I see no one.Init StateRouter BNeighbors List172.16.5.1/24, int E1I am router ID 172.16.5.2, and I see 172.16.5.1.Exchange ProcessA172.16.5.1/24E0172.16.5.2/24E1BDown StateI am router ID 172.16.5.1 and I see no one.Init StateRouter BNeighbors List172.16.5.1/24, int E1I am router ID 172.16.5.2, and I see 172.16.5.1.Router ANeighbors List172.16.5.2/24, int E0Two-Way StateDiscovering RoutesDRE0172.16.5.3E0172.16.5.1Exstart Stateafadjfjorqpoeru39547439070713HelloI will start exchange because I have router ID 172.16.5.1.No, I will start exchange because I have ahigher router ID.afadjfjorqpoeru39547439070713HelloDiscovering RoutesDRE0172.16.5.3E0172.16.5.1afadjfjorqpoeru39547439070713HelloExstart StateI will start exchange because I have router ID 172.16.5.1.No, I will start exchange because I have ahigher router ID.Exchange StateHere is a summary of my link-state database.afadjfjorqpoeru39547439070713Helloafadjfjorqpoeru39547439070713DBDafadjfjorqpoeru39547439070713DBDHere is a summary of my link-state database.Discovering RoutesDRE0172.16.5.1E0172.16.5.3afadjfjorqpoeru39547439070713afadjfjorqpoeru39547439070713LSAckThanks for the information!LSAckDiscovering RoutesDRE0172.16.5.1E0172.16.5.3afadjfjorqpoeru39547439070713afadjfjorqpoeru39547439070713LSAckThanks for the information!LSAckLoading Stateafadjfjorqpoeru39547439070713LSRI need the complete entry for network 172.16.6.0/24.afadjfjorqpoeru39547439070713Here is the entry for network 172.16.6.0/24.afadjfjorqpoeru39547439070713LSAck Thanks for the information!LSUDiscovering RoutesDRE0172.16.5.1E0172.16.5.3afadjfjorqpoeru39547439070713afadjfjorqpoeru39547439070713LSAckThanks for the information!LSAckLoading Stateafadjfjorqpoeru39547439070713LSRI need the complete entry for network 172.16.6.0/24.afadjfjorqpoeru39547439070713Here is the entry for network 172.16.6.0/24.LSUafadjfjorqpoeru39547439070713LSAck Thanks for the information!Full StateMaintaining Routing InformationLink-State ChangeDRx1 LSUAB• Router A tells all OSPF DRs on 224.0.0.6Maintaining Routing Information2Link-State ChangeDRLSUxBA• DR tells others on 224.0.0.5Maintaining Routing InformationLink-State Change2DRxAB3LSUMaintaining Routing InformationLSULSAIs entry inlink-statedatabase?Is seq.
#the same?YesNoNoAdd to databaseSend LSAckto DRYesIs seq. #higher?NoRun SPF to calculatenew routing tableSend LSUwith newerinformation tosourceEndEndFlood LSASingle Area OSPFConfigurationIgnore LSAYesConfiguring OSPF routing process• OSPF routing uses the concept of areas.• Each router contains a complete database of link-statesin a specific area.• An area in the OSPF network may be assigned anynumber from 0 to 65,535.• A single area is assigned the number 0 and is known asarea 0.• In multi-area OSPF networks, all areas are required toconnect to area 0.
Area 0 is also called the backbonearea.Enabling OSPF• Each router contains a complete database oflink-states in a specific area.• An area in the OSPF network may be assignedany number from 0 to 65,535.• A single area is assigned the number 0 and isknown as area 0.• In multi-area OSPF networks, all areas arerequired to connect to area 0. Area 0 is alsocalled the backbone area.• To enable OSPF routing, use the globalconfiguration command syntax:Router(config)#router ospf process-idConfiguring network• IP networks are advertised as follows in OSPF:Router(config-router)#network address wildcard-maskarea area-id• The network address can be a whole network, asubnet, or the address of the interface.• The wildcard mask represents the set of hostaddresses that the segment supports.Basic OSPF ConfigurationOSPF Router ID• When the OSPF process starts, the Cisco IOSuses the highest local active IP address as itsOSPF router ID.• If there is no active interface, the OSPF processwill not start.• To ensure OSPF stability, loopback interface isused, the highest loopback IP address is usedas router ID.
If there is no loopback interface,then other interface types are considered.Configure Loopback Interface• To create and assign an IP address to aloopback interface use the followingcommands:Router(config)#interface loopback numberRouter(config-if)#ip address ip-address subnet-mask• This loopback interface should be configuredwith an address using a 32-bit subnet mask of255.255.255.255.DR Election• The interface reporting the highest priority for a routerwill ensure that it becomes the DR.
Характеристики
Тип файла PDF
PDF-формат наиболее широко используется для просмотра любого типа файлов на любом устройстве. В него можно сохранить документ, таблицы, презентацию, текст, чертежи, вычисления, графики и всё остальное, что можно показать на экране любого устройства. Именно его лучше всего использовать для печати.
Например, если Вам нужно распечатать чертёж из автокада, Вы сохраните чертёж на флешку, но будет ли автокад в пункте печати? А если будет, то нужная версия с нужными библиотеками? Именно для этого и нужен формат PDF - в нём точно будет показано верно вне зависимости от того, в какой программе создали PDF-файл и есть ли нужная программа для его просмотра.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
