A simple tool to measure behavior of your friendly neighborhood NAT device

natstat records how NAT behaves in a network. This is done by sending packets from a client with source port between 1-65535 through a NAT device, then recording the observed reflexive source port as seen by a public server.

This is done multiple times per source port in order to surface any patterns that may emerge.

Make sure to run the server without any NAT so that source ports are directly observed.

docker compose build server
docker compose up server

Run the client to send NAT probes to the server. The client should be behind one or more NATs to observe the reflexive port allocated.

Ensure you run the client with the same magic integer as you provided the server.

docker compose build server
docker compose up client

natstat client -s 10.0.0.72 -d 100.0.0.92:10080 -m 1234

natstat server -l 100.0.0.92:10080 -m 1234