TCP Port remote testing "Appliance"

[LJP1]

I am looking for ideas to have a relatively inexpensive and simple hardware device that can be sent to the field to test an Ethernet port for proper TCP port connection rights.

Application is to pre-test and verify router, switch and firewall rules have been properly setup for a device, with static IP, which is allow to send/rcv specific port traffic, such as DNP-IP(20000), Modbus-TCP (502), Configuration Software (7700), etc. If I can preconfigure and send out one or more of these simple "hardware appliances" to a IT tech to plug into an ethernet port, I could test remotely and avoid wasted trips and/or on-site troubleshooting time for basic network configuration items.

A basic remote test would be something like a serial server with a serial loopback plug, configured with static IP and TCP port(of my choosing). I could then test remote connection with Putty to see echoed characters as I type.

A more advance solution could still remotely monitor and configure, but would also talk peer-to-peer to another same device on the local LAN thru specific TCP ports.

Let me know any thoughts or suggestions.