I am trying to route traffic from a small dedicated appliance to a raspberry Pi internally on my network. I have an EdgeRouter X v1.8.5. I can't modify the appliance but I can intercept its packets and its DNS lookups. It sends an http request to a web server (non https) over the internet, lets say its address is 5.5.5.5 for this example. On my network I have a small raspberry device that I want to process the data from this appliance. Both of these devices are on the same subnet (switch0) and even port (eth2). My best case scenario would be to use the tee option with iptables to make a copy of the packets and send them on to my RPi as I don't want to totally stop them from getting to the host, but the tee option is not available. I can get the data on my RPi and process it and forward it on again to the correct host. I tried useing a desitnation NAT but the address gets translated to the host on my local network but the sending host is not expecting a response from it.
Is there some way to do this through either NAT or though a DNS entry on the router that will only work for the single appliance so the RPi can still lookup the address correctly?
Thanks for the help.
