How to configure GRE Tunnel on Cisco IOS Router

Lessons Discussion
40

Dear Rene,

  1. Can you please tell why did you used:

tunnel source fastEthernet 0/0

and not:

tunnel source 192.168.12.1

instead? What would be the difference ?

  1. Now, this might sound silly but anyway … Given the below config:
HQ(config)#interface tunnel 1
HQ(config-if)#tunnel source fastEthernet 0/0
HQ(config-if)#tunnel destination 192.168.23.3
HQ(config-if)#ip address 192.168.13.1 255.255.255.0

what I still cannot understand (I have read a couple of articles on GRE) and seems very strange to me is how the ip address of the tunnel is 192.168.13.1 and the source is the ip of another (??) interface (which is fa 0/0 - 192.168.12.1).
To my common sense the source should be 192.168.13.1.

  1. Why do some tunnels are mentioning loopback interfaces as source interfaces, instead of serial0 or its ip?

I know I am wrong but I still cannot understand it … :((

Thank you!

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