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CCNP SWITCH Portable Command Guide: Implementing Inter-VLAN Routing

Inter-VLAN Communication Tips

  • Although most routers support both Inter-Switch Link (ISL) and Dot1Q encapsulation, some switch models support only Dot1Q, such as the 2950 and 2960 series.
  • If you need to use ISL as your trunking protocol, use the command encapsulation isl x, where x is the number of the VLAN to be assigned to that subinterface.
  • Recommended best practice is to use the same number of the VLAN number for the subinterface number. It is easier to troubleshoot VLAN 10 on subinterface fastethernet0/0.10 than on fastethernet0/0.2.
  • The native VLAN (usually VLAN 1) cannot be configured on a subinterface for Cisco IOS releases that are earlier than 12.1(3)T. Native VLAN IP addresses will, therefore, need to be configured on the physical interface. Other VLAN traffic will be configured on subinterfaces:
    Router(config)#interface fastethernet 0/0
    Router(config-if)#encapsulation dot1q 1 native
    Router(config-if)#ip address
    Router(config-if)#interface fastethernet 0/0.10
    Router(config-subif)#encapsulation dot1q 10
    Router(config-subif)#ip address
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