Cisco 数据中心之 HSRP, vPC 以及 vPC Peer-Gateway 介绍

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1、HowHSRPWorksHotStandbyRoutingProtocolisawell-knownfeatureofCiscoIOS. ThegoalofHSRPistoprovidearesilientdefault-gatewaytohostsonaLAN. ThisisaccomplishedbyconfiguringtwoormorerouterstosharethesameIPaddressandMACaddress. HostsontheLANareconfiguredwithasingledefault-gateway(eitherstaticallyorviaDHCP).

2、Uponsendingitsfirstpackettoanothersubnet,thehostARPsfortheMACaddressofthedefaultgateway. ItreceivesanARPreplywiththevirtualMACoftheHSRPgroup. TheIPpacketisencapsulatedinanEthernetframewithadestinationMACaddressofthedefaultgateway. Iftheprimaryrouterfails,HSRPkeepalivesarelost,andthestandbyHSRProut

3、ertakesoverthevirtualIPaddressandMACaddress. Thehostdoesnotneedtoknowthatanythinghaschanged.Inthediagramabove,theuser(10.1.1.100)isconfiguredwithadefault-gatewayof10.1.1.1. Whentheusersendsitsfirstpacketto10.5.5.5,itARPsfor10.1.1.1. Inmyexample,RouterAistheHSRPprimaryrouter,soitsendsanARPreplywith

4、thevirtualMACaddressof0000.0c07.AC05. TheUserPCthenencapsulatestheIPpacket(destinationIP=10.5.5.5)inanEthernetframewithadestinationMACaddressof0000.0c07.AC05. RouterAacceptstheframeandroutesthepacket.TheaboveparagraphstellthestoryofpacketscomingfromtheHSRP-enabledLAN. Butwhathappenstoreplypacketsc

5、omingfrom10.5.5.5to10.1.1.100? Theanswerissimple,andintuitiveifyoufollowstep-by-step. First,theServercreatesanIPpacketwithadestinationof10.1.1.100. ItencapsulatesitinanEthernetframeandforwardsittoitsdefaultgateway(forthisexample,let’ssayitisRouterA). RouterAstripstheEthernetframinganddeterminesthe

6、nexthopisonthelocalsubnet10.1.1.0/24. ItencapsulatesthepacketinanEthernetframewithaMACaddressof0021.6a98.1952. ThesourceMACaddressisthephysicalMACaddressofRouterA(0024.F71E.3343). RouterAdoesnotusethevirtualMACaddressforpacketsitroutesontothelocalsubnet.SoWhatisvPC?Nowthatwe’vecoveredHSRP,let’stal

7、kaboutVirtualPortChanneling(vPC). vPCallowstwoNX-OSdevicestoshareaport-channel. Attacheddevicesbelievethattheyareconnectedtoasingledeviceviaanetherchannelbundle. Thisisgreatbecauseiteliminatesspanning-treeblockin