Router-on-a-Stick Tips

• The 1900 series switch has ISL capability only. If connecting a router to a 1900 series switch, replace the router command encapsulation dot1q x with encapsulation isl x.

• The native VLAN (usually VLAN 1) cannot be configured on a logical subinterface in Cisco IOS Software releases earlier than 12.1(3)T. Native IP addresses therefore have to be configured on the physical interface:

  Router(config)#int fa 0/0 Router(config-if)#encapsulation dot1q 1 native Router(config-if)#ip address 192.168.1.1 255.255.255.0 Router(config-if)#int fa 0/0.10 Router(config-subif)#encapsulation dot1q 10 Router(config-subif)#ip address 192.168.10.1 255.255.255.0 

  
  

• The 1721 and the 1760 series routers have Dot1Q capability only. They cannot perform ISL encapsulation.

• The 2620 and 2621 series routers have both Dot1Q and ISL encapsulation methods.

• The number of the subinterface can be any number from 04294967295.

• Use the same number of the VLAN number for the subinterface number. Troubleshooting VLAN 10 on subinterface fa 0/0.10 is more intuitive than troubleshooting it on fa 0/0.2.

• On a 1721 or 1760 series router, the name of the Fast Ethernet interface is fa 0.x.

• On a 2620 or 2621 series router, the name of the Fast Ethernet interface is fa 0/0.x or 0/1.x.