cisco路由器的trunk与子接口的讨论

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1、Cisco路由器的Trunk与子接口的讨论First,lookatthesubinterfacenumbers.Thesubinterfacenumberbeginswiththeperiod,like.10and.20inthiscase.Thesenumberscanbeanynumberfrom1upthroughaverylargenumber(over4billion).Thenumberjustneedstobeuniqueamongallsubinterfacesassociatedwiththi

2、sonephysicalinterface.Infact,thesubinterfacenumberdoesnotevenhavetomatchtheassociatedVLANID.(Theencapsulationcommand,andnotthesubinterfacenumber,definestheVLANIDassociatedwiththesubinterface.)（案：也就是说路由器子接口的number与encapsulationdot1Q后面的number可以不一致，接收特定VLAN的帧时，

3、起作用的是encapsulationdot1Q后面的number如：encapsulationdot1Q：启用路由器的802.1Q封装，此e0/0.111只接收vlan10的数据帧。）Each802.1QtrunkhasonenativeVLAN，andwhenused,theconfigurationtousethatnativeVLANdiffers,withtwooptionsfortheroutersideofconfiguration:Routerside:1、Configuretheipaddres

4、scommandonthephysicalinterface,butwithoutanencapsulationcommand;therouterconsidersthisphysicalinterfacetobeusingthenativeVLAN.（案：交换机一端是nativeVLAN是1，路由器一端为：也可以是：）2、Configuretheipaddresscommandonasubinterface,andusetheencapsulation...nativesubcommand.（如果不指定dot

5、1Q的封装，那么子接口IP无法配到子接口下面。）最后需要注意：NOTEAlthoughnotrequired,mostsitesdochoosetomakethesubinterfacenumbermatchtheVLANID!Eachsubinterfaceconfigurationliststwosubcommands.Onecommand(encapsulation)enablestrunkinganddefinestheVLANwhoseframesareconsideredtobecominginan

6、doutofthesubinterface.Theipaddresscommandworksthesamewayitdoesonanyotherinterface.NotethatifthephysicalEthernetinterfacereachesanup/upstate,thesubinterfaceshouldaswell,Eachsubinterfaceconfigurationliststwosubcommands.Onecommand(encapsulation)enablestrunkinga

7、nddefinestheVLANwhoseframesareconsideredtobecominginandoutofthesubinterface.Theipaddresscommandworksthesamewayitdoesonanyotherinterface.NotethatifthephysicalEthernetinterfacereachesanup/upstate,thesubinterfaceshouldaswell,提问：Router端的nativeVLAN与Switch端的native

8、VLAN不一致，Trunk是否起的来？通过gns3的实验，Trunk链路可以启用，正常使用！也就是说：Router：Switch：Router与Swtich可以ping通！在Router上可以用showvlans查看相关：结论：theshowvlanscommandonarouterspellsoutwhichroutertrunkinterfacesusewhichVLANs,whi