OSPF在NBMA下的五种网络类型

OSPF在NBMA下的五种网络类型与以太网一类的Broadcast网络的区别：所谓NBMA(non-broadcastmultipleaccess)就是一个多路访问链路，但不能发广播。最典型的多路访问链路就是常见的以太网，多个访问节点都可以访问同一个网段。在以太网上是可以发广播的。所以叫BMA。NBMA阻隔广播和组播，在帧中继中，缺省类型就是NBMA。因为它是多路访问链路，但是又由于有带宽的限制不能发广播包。在以太网中，如果你想给同一子网中的多台主机发送广播(组播)包，怎么发？很简单，你发一个包就行了，所有的主机都收得到，这就是广播网的特性。再来看帧中继，我们以全互联为例，虽然所有的主机都处在同一个子网之中，但是你不可能发一个包让所有的主机都收到，因为实际上这个全互联是由多个点对点组成的，要让子网中的所有成员都收到这个广播包，你只能通过所有VC向外发送这个广播包，有几条VC就需要发送几个包。这就是NBMA网络的特性。如果OSPF不知道底层网络的通讯特性，它就不能正常工作。所以，运行于FR网络之上的OSPF，即使你把接口的网络类型改为broadcast，它也不是以太网的broadcast。所以才会有“OSPF在NBMA网络中的五种网络类型”这种说法。如果手工用单播地址指定邻居，则OSPF在向和这些组播地址发送消息的同时，也会以单播的形式向相关主机发送路由信息，在这种情况下，我们还可以选择关闭组播发送路由信息的功能，这样就只有静态配置的邻居可以收到路由信息了，提高了安全性，也减少了对无关路由器的影响RequestForComments(RFC)，是一系列以编号排定的文件。RFC编辑者负责RFC以及RFC的整体结构文档，并维护RFC的索引。ospf把NBMA分为5类分别是RFC的：point-to-multipointnon-broadcastCISCO的：point-to-multipointnonbroadcastbroadcastpoint-to-point在NBMA网络下5种网络类型具体情况如下所示:网络类型邻居自动发现有无DRHello间隔传输方式Non_broadcast否有30s单播Broadcast是有10s组播Point-to-Point是无10s组播Point-to-Multipoint是无30s组播Point-to-Multipoint(nonbroadcast)否无30s单播如果在frame-relaymap语句中使用了broadcast关键字，那网络就是广播类型。你把默认的NBMA改成broadcast就可以发现邻居了。如果不在帧中继映句中使用broadcast,则广播信息不能通过，这时候就只能手工指邻居。帧中继中的广播多路访问模式，是指在接口上打上ipospfnetworkbroadcast后欺骗ospf将hello包以广播形式发送出去，但帧中继是无法传播广播的，ospf通过DLCI中的broadcast来为每个具有DLCI的目的IP发送单播hello包。注意回复hello包也是单播形式艮L单播方式的hello包，形式上是借助端口下配置OSPF的broadcast方式广播出去，但在帧中继网络中，最终还是借助帧中继的broadcast方式来封装广播包为帧中继的单播包并转发。frame-relaymapipa.b.c.d110broadcast实验基本配置:R1/24R1：interfaceSerial0/0ipaddressencapsulationframe-relayframe-relaymapip102ping通R1frame-relaymapip102frame-relaymapip103R2：interfaceSerial0/0ipaddressencapsulationframe-relayserialrestart-delay0 默认frame-relaymapip201frame-relaymapip201ping通R2frame-relaymapip201R3：interfaceSerial0/0ipaddressencapsulationframe-relayserialrestart-delay0frame-relaymapip301frame-relaymapip301frame-relaymapip301此时R1、R2、R3都能相互ping通R1：routerospf100router-idlog-adjacency-changesnetwork55area0network55area0R2：routerospf100router-idlog-adjacency-changesnetwork55area0network55area0R3：routerospf100router-idlog-adjacency-changesnetwork55area0network55area0Type1 Non_Broadcast(默认)Rl#showipospfneighborRl#|在R1上showipospfneighbor,发现没有邻居。说明在这种情况下邻居需要手动配置R1：routerospf100neighborneighborR1(config-router)showipospfneiNeigliiziurIDPriStateDeadTimeAddressInterface2-2.2.21FULL/DROTHER00:01:54Serial0/03-3・3・31FULL/DR□0:01:56192.16S.1.3Serial0/0如果发现DR是,clearipospfproR2ttshoTiTipospfneiNeigliljurIDPriStateDeadTirn已AddressInterface1.1.!■11FULL/DROTHER00:01:44192.16S.!■1SerialO/n

R3#showipospfneiNeighborIDPri State 1 FULL/BDRDeadTime00:01:41R3#showipospfneiNeighborIDPri State 1 FULL/BDRDeadTime00:01:41AddressInterfaceSerial0/0发现邻居已经形成并且有DR与BDR的选举!R3(config)Srouterospf100R3(config-router)#neiR3(config-router)#neighbor192.16S.1.1R3(config-router)#neighborR3(config-router)ZR3#show*Mar100:48:02.147:%SYS-5-CONFIG_I:ConfiguredfromconsolebyconsoleR3#showipospfneiNeighborIDPriStateDeadTimeAddressInterfaceN/A□ATTEMPT/DROTHER□0:01:29Serial0/01FULL/BDR00:01:50Serial0/0R3#*Mar100:49:45；.443:%OSPF-5-ADJCHG：Process100^Mbr0.0.□.0onSerial0/0fromATTEMPTtoDOWN,NeighborDown::DeadtimerexpiredR3#showipospfneiNeighhorIDPriStateDeadTirn已AddressInterfaceN/A0ATTEMPT/DROTHER—Serial0/01FULL/BDR□0:01:53Serial0/0在路由器R2、R3上设置优先级为0,这个配置导致路由器R1变成dr,没有bdr被选择。R1(config-if)#ipospfprfconfig-if)#ipospfpriority?<0-255>PriorityR1(config-if)#ipospfpriority10P(config)#ints0/0(config-if)#ipospfpR2(config-if)#ipospfpriority0R3(config)#ints0/0R3(config-if)#ipospfpR3(config-if)#ipospfpriority□重启R1ospfClearipospfprocessRl#shipospfneiNeigliborIDPriStateDeadTimeAddressInterface0FULL/DROTHER00:01:53Serial0/0B.3二3.30FULL/DROTHER00:01:36Serial0/0R2#shipospfneiNeigliborIDPriStateDeadTimeAddressInterface10FULL/DR□0:00:31Serial0/0R3#shipospfneibleigliborIDPriStateDeadTimeAddressInterface10FULL/DR□0:01:28Serial0/0邻居已经形成并且有DR无BDRRl#showipospfinterfaceSerialO/OisuprlineprotocolisupInternetAddress/24,Area0ProcessID100^RouterID,NetworkTypeNON_EROADCAST,Cost:64TransmitDelayis1sec,StateDR,Priority10DesignatedRouter(ID),InterfaceaddressNobackupdesignatedrouteronthisnetworkTinierintervalsconfigured^Hello30,Dead120^Wait12QfRetransmit5oob-resynctimeout12□Helloduein 14Index1/1ffloodqueuelength0Next0x0(0)/0x0(□)Lastfloodscanlengthis2finaxitnumis2Lastfloodscantinieis□nisec^maximuinis4msec在R1上查看接口R1#showipospfinterfaceNetworkTypeNON_BROADCAST,Cost:64Timerintervalsconfigured,Hello30,Dead120,Wait120,Retransmit5Priority=10,在R1上查看接口R1#showipospfinterfaceNetworkTypeNON_BROADCAST,Cost:64Timerintervalsconfigured,Hello30,Dead120,Wait120,Retransmit5Priority=10,默认为1在这种网络类型中，hello的间隔是30s。打开debug信息，我们可以看到在这种网络类型中，OSPF的数据包是单播传送的。R1#lIpIjugipospfhelloOSPFhelloeventsdeljurgingisonRl#*Mar1UU:14:35.667：OSPF:Send.he1Iotoarea□onSerial0/0frriin1UU:14:3.5.667：OSPF:Sendhe1Into192.16S.1.3area□onSerial0/0trciiuRl#*Mar1UU:14:4U.U75:OSPF:RevhellofiruinareaU:fromSerial0/0192.16S.1.21UU:14:4U.U75:OSPF:EndOfhe11OpEuCESsingRl#*Mar1UU:14:.53.811：OSPF:Rc-vhellofruinareaU:fromSerial0/0*Nar1UU:14:.53.811:OSPF:Endofhe1lopirocpssingRl#*Mar1UU:15:0.5.667:OSPF:Sendhe1lotoareaUonSerial0/0frurri*Nar1UU:15:05.667：OSPF:Sendhe1lotoarea□onSerial0/0frrunRlttclekiuijripuspfhello1UU：15:10.027:OSPF:Revhe：llofruinareaUfroitiSerialu/0192.168.1.?*Nar1UU:15:1U.U27:OSPF:EndofhelloprricpssingType2 Broadcast首先去掉刚才手动配置的邻居关系:R1(config)#routerospf100R1(config-router)#noneighborR1(config-router)#noneighbor将R1、R2和R3接口的网络类型改成broadcastR1(config-router)#ints0/0R1(config-if)#ipospfnetworkbroadcastR2(config-router)#ints0/0R2(config-if)#ipospfnetworkbroadcastR3(config-router)#ints0/0R3(config-if)#ipospfnetworkbroadcast把各路由器的frame-relaymap命令加broadcast如：frame-relaymapip201b一会我们就看到了如下信息R3#*Mar100:15:12.175:%OSPF-5-ADJCHG:Process100,NbronSerial0/0fromLOADINGtoFULL,LoadingDone这说明了在这种网络类型下是不需要手动配置邻居关系的！有DR与BDR的选举R2#showipospfinterfaceSerialO/0isup,lineprotocolisupInternetAddress/24,Area0ProcessID100,RouterIDfNetworkTypeEROAPCASTfCost:€4TransmitDelayis1sec,StateDROTHER,Priority0DesignatedRouter[ID}1.1.1.InterfaceaddressNobackupdesignatedrouteronthisnetworkTimerintervalsconfigured,Hello10,Dead40fWait40fRetransmit5□□b-resynctimeout40Helloduein00:00:01Index1/1ffloodqueuelength0Next0x0(0)/0x0(0)Lastfloodscanlengthis1fmaxinuuniis1Lastfloodscantineis0msecfmaxiiminiis□msecNeighborCountislfAdjacentneighborcountis1Adjacentwithneigtibor[DesignatedRouter)Suppresshellofor0neigirbor(s)ProcessID100,RouterID,NetworkTypeBROADCAST,Cost:64Timerintervalsconfigured,Hello10,Dead40,Wait40,Retransmit5Hello时间间隔为10s。*Mar1*Mar100:15:12.175:OSPF*Mar100:15:12.279:OSPF*Mar100:15:12.279:OSPF*Mar100:15:22.155:OSPF*Mar100:15:22.155:OSPF*Mar100:15:22.175:OSPFR2#debugipospfhelloSendhellotoarea0onSerial0/0fromRcvhellofromarea0fromSerial0/0EndofhelloprocessingRcvhellofromarea0fromSerial0/0EndofhelloprocessingSendhellotoarea0onSerial0/0from使用这个组播地址传送数据包。Type3 Point-to-Point将R2,R3接口的网络类型改成Point-to-PointR2(config-if)#ipospfnetpoint-to-point此时，R1还是BROADCAST没有DR/BDR的选举LOADINGtoFULL,LoadingDone说明这种网络类型也不需要手动指定邻居此时，执行R1(config-if)#ipospfnetpoint-to-point网络将变得不稳定

R1(config-if}#*Mar100:39:03.199:%OSPF-5-ADJCHG:Process100fAdjacencyforcedtoreset*Mar100:39:03,403:%OSPF-5-ADJCHG:Proc已mm100fn:Adjacencyforcedtoresat*Mar100:39:03,495:%OSPF-5-ADJCHG:Process100rwn:Adjacencyforcedtoreset*Mar100:39:03.603:%R1(config-if}#*Mar100:39:03.199:%OSPF-5-ADJCHG:Process100fAdjacencyforcedtoreset*Mar100:39:03,403:%OSPF-5-ADJCHG:Proc已mm100fn:Adjacencyforcedtoresat*Mar100:39:03,495:%OSPF-5-ADJCHG:Process100rwn:Adjacencyforcedtoreset*Mar100:39:03.603:%OSPF-4-NONEIGHBOR:ReceivedR1(config-if}#*Mar100:39:04.227:%OSPF-5-ADJCHG:Proc已mm100fR1(config-if}#*Mar100:39:08.103:%OSPF-5-ADJCHG:Process100fAdjacencyforcedtoreset*Mar100:39:09.023:%OSPF-5-ADJCHG:Process100fR1(config-if}#*Mar100:39:13.199:%OSPF-5-ADJCHG:Proc已mm100fAdjacencyforcedtoreset*Mar100:39:13.295:%OSPF-4-NONEIGHBOR:ReceivedR1(config-if}#*Mar100:39:13,415:%OSPF-5-ADJCHG:Process100fwn:Adjacencyforcedtoreset*Mar100:39:13.619:%OSPF-5-ADJCHG:Proc已mm100fwn:AdjacencyforcedtoresetHl.fugfzL口-： NbronSerial0/0Nbr3■3■3-3onSerial0/0NbronSerial0/0fromFULLtoDOWN,NeighborDown:fromEXSTARTtoDOWNfNeighborDawfromEXCHANGEtoDOWN,NeighborDodatabasedescriptionfromunknownneighborNbr3■3■3-3onSerial0/0fromLOADINGtoFULL,LoadingDaneNbr3■3■3-3NbronSerial0/0fromFULLtoDOWN,NeighborDown:onSerial0/0fromLOADINGtoFTO.LrNbronSerial0/0fromFULLtoDOWNfLoadingDoneNeighborDown:databasedescriptionfromunknownneighborNbr3.3.3・3onSerial0/0fromEXCHANGEtoDOWN,NeighborDoNbronSerial0/0fromEXCHANGEtoDOWN,NeighborDaR2(config-if)#doshowipospfintSerial0/0isupFlineprotocolisupInternetAddress/24rArea0ProcessID100rRouterIDrNetworkTypePOINT_TO_POINTfCost:€4TransmitDelayis1secFStatePOINT_TO_POINTrTimerintervalsconfigured.Hello10rDead40rWait40rRetransmit5oob-r已mynutimeout40Helloduein00:00:04Indexl/lrfloodqueuelength0Next0x0£0)/0x0(0)Lastflood,scanlengthis1fmaxinmniis1Lastfloodscantimeis0msecFmaxinmniis0msecNeigtiborCountislrAdjacentneighborcountis1AdjacentwithneighborSuppi?3mhell。En已：Lghbmc(m)Timerintervalsconfigured,Hello10,Dead40,Wait40,Retransmit5Hello时间间隔为10sR2#debugipospfhello*Aug1415:08:25.311:OSPF:Sendhellotoarea0onSerial0/0fromR2#*Aug1415:08:30.259:OSPF:Rcvhellofromarea0fromSerial0/0*Aug1415:08:30.263:OSPF:Endofhelloprocessing同样也是使用这个组播地址传送数据。重新规划pointtopointR1重启路由器去掉前面的配置。R1:interfaceSerial0/0noipaddressencapsulationframe-relayinterfaceSerial0/0.20point-to-pointipaddressframe-relayinterface-dlci102interfaceSerial0/0.30point-to-pointipaddressframe-relayinterface-dlci103routerospf100network55area0network55area0R2:interfaceSerial0/0ipaddressencapsulationframe-relayipospfnetworkpoint-to-pointframe-relaymapip201routerospf100network55area0R3:interfaceSerial0/0ipaddressencapsulationframe-relayframe-relaymapip301broadcastnoframe-relayinverse-arprouterospf100network55area0R2:frame-relaymapip201broadcastSerial0/OisuprlineprotocolisupInternetAddress/24fArea0ProcessID100fRouterIDfNetworkTypePOINT_TO_POINTfCost:64TransmitCtelayis1secrStatePOIErT_TO_POINTfTimerintervalsconfigured.Hello10fDeadWait40fRetransmit5□□b-resynctimeout40Helloduein00:00:07Index1/1ffloodqueuelength0Next0x0(0)/0x0[0}Lastfloodscanlengthislfmaxiiuuiuis1Lastfloodscantimeis0msecfmaximLiniis0msecNeigtiborCountislfAdjacentneigtiborcountis1AdjacentwithneigtiborSuppi?已mmh巳]口Ecii?口n巳ighbcii?(m)Type4 Point-to-Multipoint将接口改为Point-to-MultipointR1(config-if)#ipospfnetworkpoint-to-multipointR2(config-if)#ipospfnetworkpoint-to-multipointR3(config-if)#ipospfnetworkpoint-to-multipointLOADINGtoFULL,LoadingDone同样也不需要手动指定邻居没有DR和BDR的选举R2#shipospfintSerial0/Oisup,lineprotocolisupInternetAddress/24,Aj?ea0ProcessID100fRouterIDfNetworkTypePOINT_TO_MULTIPOINTfCost:岳啜TransmitDelayis1sec,StatePOINT_TO_MULTIPOINTfTimerintervalsconfigured.Hello30,Dead120,Wait120,Retransmit5oob-resynctimeout120Helloduein00:00:00Index1/1ffloodqueuelength0Next0x0[0)/0x0[0}Lastfloodscanlengthislfmaximiiniis1Lastfloodscantimeis0msec,nkaxinniniis0msecNeighborCountislfAdjacentneighborcountis1AdjacentwithneighborSuppresshellofor0neiglibor(s)NetworkTypePOINT_TO_MULTIPOINTHello30,Dead120,Wait120,Retransmit5Hello时间间隔为30sR2#*Har101:16:15.395:OSPF:Sendhelloto22^.0.0.5area0onSerialO/0fromR2#*Har101:16:40.587:OSPF:Revhellofromarea0fromSerialO/0*Mar101:16:40.587:OSPF:EndofhelloprocessingR2f*Mar101:16:45.395:OSPF:SendhelloCoarea0o