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I have Router 1 with the following interfaces:

  • FA0/1:
  • S0/0/0:
  • S0/0/1:

This is for my assignment at university, there should be a computer connected to the FA0/1 interface of this router, the computer should have these details:

  • IP:
  • Subnet:
  • Default Gateway:

As I don't have a computer available to connect to the router I was told to use a loopback interface to virtualise this.

Please help me on setting up this loopback.

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A loopback interface and an attached computer aren't the same kind of thing. What is the actual goal? –  Bill Weiss Mar 4 '12 at 23:36
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2 Answers

Just do as you would do with a regular interface:

conf t 
int loopback 1
ip address 
no shut

Now enable routing for that subnet on your router and you are all set.

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THE Ip used for FA0/1 is says the loopback overlaps it.... –  Jack Brown Mar 4 '12 at 18:46
Updated, sorry it's getting late, is it working ? –  Lucas Kauffman Mar 4 '12 at 18:47
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Another solution would be to disable the keepalive on the FastEthernet to artificially bring it up :

Router(config)# interface FastEthernet0/1
Router(config)# no keepalive

The interface will now show up/up even if there is no cable plugged on the interface. Therefore your router will be reachable from the wan on his Fa0/1 ( IP address.

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