MPLS-自己的经验理解通俗易懂.ppt
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MPLS-自己的经验理解通俗易懂.ppt
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MPLS及MPLSVPN基本概念,2012年3月,MPLSVPN的基本概念,目录,MPLS的基本概念,1,3,MPLS及MPLSVPN举例,传统IP路由网络的缺陷,传统的IP数据转发,使用路由协议传送IP路由信息基于IP包的目标地址进行数据转发IP包每经过一个路由器都需要进行路由表的查询,IP的逐跳转发,在经过的每一跳处,必须进行路由表的最长匹配查找(可能多次),速度缓慢。
在传统的IP转发中的流量工程问题,MosttrafficgoesbetweenlargesitesAandBandusesonlytheprimarylink.Destination-basedroutingdoesnotprovideanymechanismforloadbalancingacrossunequalpaths.Policy-basedroutingcanbeusedtoforwardpacketsbasedonotherparameters,butthisisnotascalablesolution.,PrimaryOC192link,LargeSiteA,LargeSiteB,SmallSiteC,BackupOC48link,ReviewQuestions,列出主要的传统IP路由缺点.IP包的传发是基于那一种信息?
为什么这种转发机制不适用于大型网络?
MPLS架构及相关技术,MPLS数据转发,MPLS的标签转发,通过事先分配好的标签,为报文建立了一条标签转发通道(LSP),在通道经过的每一台设备处,只需要进行快速的标签交换即可(一次查找)。
MPLS:
多协议标签交换,MPLS:
Multi-ProtocolLabelSwitching在IP网络实现2.5层数据交换,MPLS的基本概念,基于标签进行数据转发的机制标签对应于IP目标路由网络标签可对应于其他相关参数QosIP源地址支持多种协议的转发,MPLS/IP网络,MPLS架构,控制层面(Controlplane)运用路由协议进行路由信息的交换运用标签分发协议进行标签交换数据层面(Dataplane)基于标签进行数据转发,MPLSArchitecture,Routerfunctionalityisdividedintotwomajorparts:
controlplaneanddataplane,DataPlane,ControlPlane,OSPF:
10.0.0.0/8,LDP:
10.0.0.0/8Label17,OSPF,LDP,LFIB,LDP:
10.0.0.0/8Label4,OSPF:
10.0.0.0/8,LabeledpacketLabel4,LabeledpacketLabel17,LabelFormat,MPLSusesa32-bitlabelfieldthatcontainsthefollowinginformation:
20-bitlabel3-bitexperimentalfield1-bitbottom-of-stackindicator8-bittime-to-live(TTL)field,LABEL,EXP,S,TTL,0,19,22,23,31,20,24,Frame-ModeMPLS,Routinglookupandlabelassignment,LabelSwitchRouter,Labelswitchrouter(LSR)转发打了标签的IP包EdgeLSR给IP包打标签并转发到MPLS域删除标签并把IP包从MPLS域转发出去,MPLSDomain,EdgeLSR,LSR,10.1.1.1,L=3,L=5,L=43,L=31,20.1.1.1,10.1.1.1,20.1.1.1,LSR的功能架构,LSRs,regardlessofthetype,performthefollowingthreefunctions:
ExchangeroutinginformationExchangelabelsForwardpackets(LSRsandedgeLSRs)Thefirsttwofunctionsarepartofthecontrolplane.Thelastfunctionispartofthedataplane.,ArchitectureofLSRs,LSRsprimarilyforwardlabeledpackets.,LSR,ControlPlane,DataPlane,RoutingProtocol,LabelDistributionProtocol,LabelForwardingTable,IPRoutingTable,Exchangeofroutinginformation,Exchangeoflabels,Incominglabeledpackets,Outgoinglabeledpackets,ArchitectureofEdgeLSRs,EdgeLSR,ControlPlane,DataPlane,RoutingProtocol,LabelDistributionProtocol,LabelForwardingTable,IPRoutingTable,Exchangeofroutinginformation,Exchangeoflabels,Incominglabeledpackets,Outgoinglabeledpackets,IPForwardingTable,IncomingIPpackets,OutgoingIPpackets,MPLS转发,LSR功能:
插入(Insert)标签交换(Swap)标签删除(Pop)标签,MPLS域,MPLSForwarding(Frame-Mode),OningressalabelisassignedandimposedbytheIProutingprocess.LSRsinthecoreswaplabelsbasedonthecontentsofthelabelforwardingtable.Onegressthelabelisremovedandaroutinglookupisusedtoforwardthepacket.,10.1.1.1,MPLS网络IP路由示例,LSR,ControlPlane,DataPlane,OSPF:
RT:
LIB:
FIB:
LFIB:
OSPF:
10.0.0.0/8,10.0.0.0/81.2.3.4,10.0.0.0/81.2.3.4,LSR,ControlPlane,DataPlane,OSPF:
RT:
LIB:
FIB:
LFIB:
OSPF:
10.0.0.0/8,10.0.0.0/81.2.3.4,10.0.0.0/81.2.3.4,LDP:
10.0.0.0/8,L=3,10.0.0.0/8Next-hopL=3,LocalL=5,LDP:
10.0.0.0/8,L=5,MPLS网络IP路由示例,标签的分配和分发过程,IP路由协议构造IP路由表LSR对路由表中每一目标网段独立地分配标签LSR把所分配的标签公告给其他LSR根据所受到的标签,LSR构建LIB,LFIB和FIB,路由表的构建,IProutingprotocolsareusedtobuildIProutingtablesonallLSRs.FIBsarebuiltbasedonIProutingtableswithnolabelinginformation.,A,B,C,D,E,NetworkX,分配标签,EveryLSRallocatesalabelforeverydestinationintheIProutingtable.Labelshavelocalsignificance.Labelallocationsareasynchronous.,A,B,C,D,E,NetworkX,LIB和LFIB的建立,LIBandLFIBstructureshavetobeinitializedontheLSRallocatingthelabel.,A,B,C,D,E,NetworkX,标签分发LabelDistribution,TheallocatedlabelisadvertisedtoallneighborLSRs,regardlessofwhethertheneighborsareupstreamordownstreamLSRsforthedestination.,标签通告的接收(ReceivingLabelAdvertisement),EveryLSRstoresthereceivedlabelinitsLIB.EdgeLSRsthatreceivethelabelfromtheirnext-hopalsostorethelabelinformationintheFIB.,X=25,X=25,A,B,C,D,E,X=25,NetworkX,过渡期的数据传送(InterimPacketPropagation),ForwardedIPpacketsarelabeledonlyonthepathsegmentswherethelabelshavealreadybeenassigned.,IP:
X,Lab:
25,IP:
X,A,B,C,E,进一步的标签分配(FurtherLabelAllocation),EveryLSRwilleventuallyassignalabelforeverydestination.,A,B,C,D,E,NetworkX,标签通告的接收(ReceivingLabelAdvertisement),EveryLSRstoresreceivedinformationinitsLIB.LSRsthatreceivetheirlabelfromtheirnext-hopLSRwillalsopopulatetheIPforwardingtable(FIB).,A,B,C,D,E,NetworkX,增加LFIB条目(PopulatingLFIB),RouterBhasalreadyassignedalabeltoXandcreatedanentryintheLFIB.TheoutgoinglabelisinsertedintheLFIBafterthelabelisreceivedfromthenext-hopLSR.,Label,Action,Nexthop,25,47,C,LFIBonB,A,B,C,D,E,NetworkX,数据包通过MPLS网络的过程,IP:
X,IP:
X,A,B,C,E,Lab:
25,Lab:
47,MPLS网络LSP的建立,MPLS网络的优化,MPLSDomain,Doublelookupisnotanoptimalwayofforwardinglabeledpackets.Alabelcanberemovedonehopearlier
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