I follow a tutorial, there shows the method of create sub-interface:

but in my actual situation, I can not do this:

Router(config)#interface gigabitEthernet 2/1.100
% Invalid input detected at '^' marker.

my router is CGR 1240 in Cisco Packet Tracer.

  • 1
    You cant expect packet tracer to give all the real world functionalities. – user36472 Nov 7 '18 at 6:34
  • are all the routers can not create sub interfaces? – 244boy Nov 7 '18 at 6:45
  • i dont remember, but i dont think they can. – user36472 Nov 7 '18 at 6:59
  • Did the answer help you? If so you should accept the answer so that it does not keep popping up. Alternatively you can add your own answer and accept that. – user36472 Nov 15 '18 at 10:15

The GCR routers do not support the sub-interface in Packet tracer, you can change your router to a high-level router, such as ISR4321, then you can create easily for experiment:

RT1(config)#interface gigabitEthernet 0/0/0.100 
%LINK-5-CHANGED: Interface GigabitEthernet0/0/0.100, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0/0.100, changed state to up

Current router on packet tracer is not working because its IOS might be corrupted .

Try another router in packet tracer and try to configure sub-interfaces it will work .

Example as below

Router(config)# int ethernet 0/1

Router(config)#no ip address

Router(config)#no shutdown

Router(config)#int ethernet 0/1.20

Router(config)ip address X.X.X.X 255.X.X.X

Router(config)# encapsulation dot1q 20

Router(config)#no shutdown

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