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1、Configuring OSPFLink-State AdvertisementsIssues with Maintaining a Large OSPF NetworkThe Solution: OSPF Hierarchical RoutingConsists of areas and autonomous systemsMinimizes routing update traffic（划分区域可以减小路由更新的通信量）（划分区域可以减小路由更新的通信量）Types of OSPF RoutersVirtual links are used to connect a discontiguo
2、us area to area 0.(虚电路可以用于两个不连续的骨干区域虚电路可以用于两个不连续的骨干区域)A logical connection is built between router A and router B.Virtual links are recommended for backup or temporary connections.（虚电路通常用于本份或临时的连接）（虚电路通常用于本份或临时的连接）Defining Virtual Links Configuring Virtual Linksarea area-id virtual-link router-id au
3、thentication message-digest | null hello-interval seconds retransmit-interval seconds transmit-delay seconds dead-interval seconds authentication-key key | message-digest-key key-id md5 keyRouter(config-router)#Creates a virtual linkremoterouter#sh ip ospf Routing Process ospf 1000 with ID 10.2.2.2
4、Supports only single TOS(TOS0) routes Supports opaque LSA Supports Link-local Signaling (LLS) Supports area transit capability It is an area border router OSPF Virtual Link Configuration ExampleRouterA#sh ip ospf virtual-linksVirtual Link OSPF_VL0 to router 10.2.2.2 is up Run as demand circuit DoNot
5、Age LSA allowed. Transit area 1, via interface Serial0/0/1, Cost of using 781 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:07 Adjacency State FULL (Hello suppressed) Index 1/2, retransmission queue length 0, nu
6、mber of retransmission 1 First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0) Last retransmission scan length is 1, maximum is 1 Last retransmission scan time is 0 msec, maximum is 0 msecRouterA#The show ip ospf virtual-links CommandLSA TypeDescription1Router LSAs2Network LSAs3 or 4Summary LSAs5Autonomous systeme
7、xternal LSAs6Multicast OSPF LSA7Defined for not-so-stubby areas8External attributes LSA forBorder Gateway Protocol (BGP)9, 10, 11Opaque LSAsLSA TypesLSA Type 1: Router LSA （路由器（路由器LSA）One router LSA (type 1) for every router in an areaIncludes list of directly attached linksEach link identified by I
8、P prefix assigned to link and link typeIdentified by the router ID of the originating routerFloods within its area only; does not cross ABR路由器路由器LSA被被扩散到区散到区域内的所有路由器中；域内的所有路由器中；描述了与路由器相描述了与路由器相连的的所有所有链路状路状态；该类LSA不会再从不会再从ABR传递到其他区域到其他区域LSA Type 2: Network LSA（网络（网络LSA）One network (type 2) LSA for eac
9、h transit broadcast or NBMA network in an areaIncludes list of attached routers on the transit linkIncludes subnet mask of linkAdvertised by the DR of the broadcast networkFloods within its area only; does not cross ABR由一个多路由一个多路访问网网络的的DR产生；被生；被扩散到散到区域中的所有路由器；区域中的所有路由器；该类LSA包含了包含了该多多网网络所有相所有相连的路由的路由
10、器和网器和网络前前缀和掩和掩码。LSA Type 3: Summary LSA（汇总（汇总LSA）Type 3 LSAs are used to flood network information to areas outside the originating area (interarea)Describes network number and mask of link.Advertised by the ABR of originating area.Regenerated by subsequent ABRs to flood throughout the autonomous sy
11、stem.By default, routes are not summarized, and type 3 LSA is advertised for every subnet.由由ABR产生，生，这个个LSA通告了所在区通告了所在区域中的网域中的网络LSA Type 4: Summary LSA（汇总（汇总LSA）Summary (type 4) LSAs are used to advertise an ASBR to all other areas in the autonomous system.They are generated by the ABR of the origina
12、ting area.They are regenerated by all subsequent ABRs to flood throughout the autonomous system.Type 4 LSAs contain the router ID of the ASBR.由由ABR产生，通告了自治系生，通告了自治系统的的ASBR的的RID，和一条，和一条前往前往ASBR的路由的路由LSA Type 5: External LSA（外部（外部LSA）External (type 5) LSAs are used to advertise networks from other aut
13、onomous systems.Type 5 LSAs are advertised and owned by the originating ASBR.Type 5 LSAs flood throughout the entire autonomous system.The advertising router ID (ASBR) is unchanged throughout the autonomous system.Type 4 LSA is needed to find the ASBR.By default, routes are not summarized.由由ASBR产生，包
14、含了外部自治系生，包含了外部自治系统的路由的路由Interpreting the OSPF DatabaseRouterA#show ip ospf database OSPF Router with ID (10.0.0.11) (Process ID 1) Router Link States (Area 0)Link ID ADV Router Age Seq# Checksum Link count10.0.0.11 10.0.0.11 548 0x80000002 0x00401A 110.0.0.12 10.0.0.12 549 0x80000004 0x003A1B 1100.1
15、00.100.100 100.100.100.100 548 0x800002D7 0x00EEA9 2 Net Link States (Area 0)Link ID ADV Router Age Seq# Checksum172.31.1.3 100.100.100.100 549 0x80000001 0x004EC9 Summary Net Link States (Area 0)Link ID ADV Router Age Seq# Checksum10.1.0.0 10.0.0.11 654 0x80000001 0x00FB1110.1.0.0 10.0.0.12 601 0x8
16、0000001 0x00F516Interpreting the Routing Table: Types of RoutesRouter DesignatorDescriptionOOSPF intra-area (router LSA) andnetwork LSANetworks from within the area of the routerAdvertised by way of router LSAs and network LSAO IAOSPF interarea(summary LSA)Networks from outside the area of the route
17、r, but within the OSPF autonomous systemAdvertised by way of summary LSAsO E1Type 1 external routesNetworks outside of the autonomous system of the routerAdvertised by way of external LSAsO E2Type 2 external routesCalculating Costs for E1 and E2 RoutesThe show ip route CommandRouterBshow ip routeCod
18、es: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS
19、 level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static routeGateway of last resort is not set 172.31.0.0/24 is subnetted, 2 subnetsO IA 172.31.2.0 110/1563 via 10.1.1.1, 00:12:35, FastEthernet0/0O IA 172.31.1.0 110/782 via 10.1.1.1, 0
20、0:12:35, FastEthernet0/0 10.0.0.0/8 is variably subnetted, 6 subnets, 2 masksC 10.200.200.13/32 is directly connected, Loopback0C 10.1.3.0/24 is directly connected, Serial0/0/0O 10.1.2.0/24 110/782 via 10.1.3.4, 00:12:35, Serial0/0/0C 10.1.1.0/24 is directly connected, FastEthernet0/0O 10.1.0.0/24 1
21、10/782 via 10.1.1.1, 00:12:37, FastEthernet0/0O E2 10.254.0.0/24 110/50 via 10.1.1.1, 00:12:37, FastEthernet0/0ip ospf cost interface-cost Overrides the default cost calculation. Values from 1 to 65535 can be defined.Changing the Cost Metricauto-cost reference-bandwidth ref-bwSets the reference band
22、width to values other than 100 Mbps (legal values range from 1 to 4,294,967 in megabits per second).花费没有小数花费没有小数,默认是默认是100M,那那10M就是就是10,100M就是就是1,1000M也是也是1.Dijkstras algorithm determines the best path by adding all link costs along a path.The cost, or metric, is an indication of the overhead to sen
23、d packets over an interface. Default = (100 Mbps) / (bandwidth in Mbps).RouterA(config-if)#RouterA(config-router)#SummaryThere are four OSPF router types: internal routers, backbone routers, ABRs, and ASBRs.A virtual link allows discontiguous area 0 to be connected, or a disconnected area to be conn
24、ected to area 0, via a transit area. Virtual links should be used only for temporary connections or backup after a failure, not as a primary backbone design feature. There are 11 OSPF LSA types. The first five are the most commonly used:Type 1 routerType 2 networkType 3 and 4 summaryType 5 externalS
25、ummary (Cont.)In the IP routing table, OSPF routes are classified as either intra-area, interarea, or external; external routes are subdivided into E1 and E2.OSPF LSDB overload protection limits the processing of non-self-generated LSAs.The OSPF cost defaults to (100 Mbps) / (bandwidth in megabits per second). The cost can be changed on a per-interface basis, and the reference bandwidth (100 Mbps) can also be changed.
