How to create Ethernet interface at a specific IP address that I can ping and force to sometimes reply and sometimes not?

I'd like to do some experiments to test the ping and fping commands (see: https://unix.stackexchange.com/questions/678045/equivalent-of-ping-o-on-linux) , but I need a local virtual Ethernet interface to test this. I'd like to have a scenario where I can run ping 10.0.0.1 (or any other IP) and have it fail. Then, while ping is still running, I run some commands that bring up the interface and have it pass. In other words, the output of ping will change _while it is running_, as the virtual device comes "alive". I don't want to have to use physical hardware. How can I do this? I've already tried following my own instructions here (https://unix.stackexchange.com/questions/152331/how-can-i-create-a-virtual-ethernet-interface-on-a-machine-without-a-physical-ad/593142#593142) , but unfortunately even after running sudo ip link set eth10 down, pinging eth10 via ping 10.0.0.1 still succeeds. After running sudo ip link delete eth10 type dummy to delete the dummy virtual device, ping 10.0.0.1 also still succeeds. --- ## Summary of functional answers so far: (as of 22 Nov. 2021) 3 answers received (my own included), and **all 3 answers work**!: 1. [by Stephen Harris](https://unix.stackexchange.com/a/678208/114401) - use loopback sub-interfaces (probably the best answer so far) 1. [by Hauke Laging](https://unix.stackexchange.com/a/678181/114401) - use iptables 1. [my own answer](https://unix.stackexchange.com/a/678180/114401) - use virtual interfaces