I have a server hosted on OVH that I use for development and to learn Linux, Apache, and Nginx. Long story short, I'm trying to call an API hosted on this server (let's call it server B) from another server (server A) using a Python script. Here's the problem: when server A sends a POST request with a JSON payload to server B, the request does reach server B (I can see it using tcpdump), but server B does not send any ACK response or take any action. The strange part is that if I make the same POST request to server B from my local PC, it works perfectly fine, and the server responds as expected. What could be causing this issue? Could it be related to firewalls, networking, or server configurations? Any help would be appreciated. Expected Behavior: I expect the server (Server B) to respond to the POST request regardless of the source. Steps Tried: I tested the same request from another server (Server C), and in this case, Server B responds as expected. Below is an example of the network traffic captured during the tests: Server A → Server B (failing case): 09:47:56.534445 IP serverA > serverB: Flags , seq <sequence>, win 65320, options [mss 1420,sackOK,TS val <value> ecr 0,nop,wscale 7], length 0 Server C → Server B (working case): 09:47:57.534445 IP serverB > serverC: Flags [.], ack <ack_value>, win 503, options [nop,nop,TS val <value> ecr <value>], length 0 Both tests used the same API endpoint on Server B with identical payloads. Continue reading...
