BorderGatewayProtocolRouteSummarization?2003,CiscoSystems,Inc.Allrightsreserved.1ObjectivesUponcompletingthislesson,youwillbeableto:ExplainhowBorderGatewayProtocolversion4isrelatedtoclasslessinterdomainrouting(BGP4對無類域間路由的支持.)ExplainhowBorderGatewayProtocolimplementsroutesummarizationwiththenetworkcommand(用NETWORK命令實施路由匯總)DescribehowBorderGatewayProtocolimplementsroutesummarizationwiththeaggregate-addresscommand(用地址聚合命令實施路由匯總.)CIDRandAggregateAddresses

WithBGP4,routescan

beaggregatedbyany

ASonanyBGProuter.BGP4isclassless,

supportsVLSMand

longestmatchrouting,

andcarriesanetwork

maskforeachnetwork

intheupdate.BGP更新消息中包括地址前綴和前綴長度.NetworkBoundarySummarizationnoauto-summaryRouter(config-router)#

BGP,RIPv1andRIPv2,IGRP,andEIGRPperform

networkboundarysummarizationbydefault.(自動匯總)BGP,RIPv2,andEIGRPcandisable(關閉)network

boundarysummarization.CIDRhasforcedtheIANAtobeginusingclass

Aaddresses,like,inaclasslessmanner.IfyouareassignedaportionofaclassA,B,orC

address,theno-autosummarycommandneeds

tobeimplementedundertheBGPprocessoryou

riskclaimingownershipofthewholeclassA,B,

orCaddress.

networknetwork-number[masknetwork-mask]

Router(config-router)#Thiscommandwasnotdesignedtoperformsummarizationbyitself.Theaggregate-addresscommandwasdesignedforsummarization.(將外部路由宣告到BGP中去.)BGPnetworkCommandiprouteprefix

masknull0(人工創建匯總靜態路由到空端口.)Router(config)#Tousethenetworkstatementforsummarization,thenetworknumberandmaskusedmustalreadyexistintheroutingtable.IftheroutewasalreadysummarizedbyEIGRPorOSPF,thatsummarizationcanbeannouncedintoBGPwiththenetworkandmaskcommands.Iftheroutewasnotalreadysummarized,anullroutemustbecreatedforBGPtoannouncethissummarization.空端口:如果BGP路由表沒有這條匯總路由時,BGPNETWORK命令無法發布.匯總路由不能確定從哪個物理端口走,所以用空端口來決定來告訴路由器如何走CautionsaboutNetworkStatementIfanetworkstatementis

usedforsummarization,

donotusethemore

specificentriesandthe

summarizedrouteas

shownhere.Ifbothareused,the

summarizedrouteandthe

morespecificrouteswill

beannounced./22doesnot

existintheIProutingtable

withoutthenullroute.BGP

willnotannouncethenetwork

unlessthesummarizedroute

isalreadypresentinthe

routingtable.NETWORK也有間接匯總功能.要求網絡必須先存在,可以使用空端口.BGPSummarizationUsingthenetworkCommandandStaticRoutetoNull0ConfiguringBGPforAggregateAddressingaggregate-addressip-address

mask[summary-only][as-set]Router(config-router)#Createsanaggregate(summary)entryinthe

BGPtable(無須先有路由.)Usesthesummary-onlyoptiontoadvertiseonly

thesummaryandnotthespecificroutes（通告匯總路由）Addstheas-setoptiontoincludealistofallthe

autonomoussystemnumbersthatthemore

specificrouteshavepassedthrough(要求在AS屬性中列出包含具體路由的AS號，以避免環路.)mendedmethodofsummarizationforBGPNullstaticroutenotneeded;BGPnullroute

automaticallygenerated(會自動產生一條匯總路由,并且指向空端口.)BGPSummarizationUsingtheaggregate-addressCommandBGPAggregationshowipbgpNetwork/22

*>

s>s>s>s>

NextHopLocPrfWeight3276832768327683276832768

PathiiiiiMetric00000routerC#showipbgpBGPtableversionis28,localrouterIDisStatuscodes:s=s