Not Connecting

[althakar]

I am not able to connect with another user

[VaradGupta23]

Okay, let's solve this "Not Connecting" issue for your P2P application. The problem is almost always related to how your network (and the other user's network) handles incoming connections.

Here’s a step-by-step guide to help you establish a connection:

The Goal: Allow two P2P applications to "see" and communicate with each other across the internet.
Step 1: Verify the Peer's Information (Most Common Issue!)
The error message "Trying to connect to 172.19.70.136:64805" shows the IP and port your application is trying to reach. This must be the correct public IP address and listening port of the other user's P2P application.

Contact the Other User: The most critical step is to get the correct "My Wan IP" and the listening port from the other user.

They should open their P2P app and tell you their "My Wan IP" (e.g., 117.215.27.111 in your screenshot) and the port their app is actively listening on (e.g., 52855 in your screenshot).

Enter Peer IP Correctly: In your P2P application, in the "Peer IP:" field, enter the other user's public IP address followed by a colon and their listening port.

Example: If their "My Wan IP" is 203.0.113.45 and their listening port is 52855, you would enter 203.0.113.45:52855.

Crucially, do NOT enter your own WAN IP here if you're trying to connect to someone else.

Step 2: Check and Configure Firewalls (Your Computer & Their Computer)
Firewalls are designed to block unwanted incoming connections. This is a very common reason for P2P connection failures.

Windows Firewall (Your PC):

Search for "Windows Defender Firewall" in your Windows search bar and open it.

Click on "Allow an app or feature through Windows Defender Firewall" on the left.

Click "Change settings" (you might need administrator privileges).

Scroll through the list and find your P2P application (e.g., P2P or the executable name like p2p.exe).

Ensure both "Private" and "Public" checkboxes are ticked for your P2P application.

If your app isn't listed, click "Allow another app...", browse to your P2P application's executable file, add it, and then tick both "Private" and "Public" checkboxes.

Alternatively (for testing only): You can temporarily turn off the firewall (Windows Defender Firewall -> Turn Windows Defender Firewall on or off) to see if it resolves the issue. Remember to turn it back on immediately after testing!

Third-Party Antivirus/Firewall Software: If you have any other security software (e.g., Norton, McAfee, Avast, Kaspersky), it might have its own firewall. You'll need to open its settings and add an exception for your P2P application and its listening port.

Instruct the Other User: The other user must perform these same firewall checks and configurations on their computer.

Step 3: Utilize STUN/TURN (If Your App Supports It)
Your application has a "Stun" tab, which is a good sign. STUN (Session Traversal Utilities for NAT) and TURN (Traversal Using Relays around NAT) are technologies designed to help P2P applications bypass NAT and firewalls automatically.

Explore the "Stun" Tab:

Click on the "Stun" tab in your application.

Look for options to enable STUN or enter STUN server addresses. Many apps will have default STUN servers pre-configured.

Ensure STUN is enabled or configured correctly. The application uses STUN to discover its own public IP and the type of NAT it's behind.

Relay (TURN) Servers: If STUN fails to establish a direct connection (often due to restrictive NATs on one or both sides), a TURN server acts as a relay, forwarding traffic between the two peers. Your application might automatically fall back to TURN if STUN fails, or it might have a separate configuration for it.

Step 4: Router Configuration (Port Forwarding - Advanced / Last Resort)
This step is more complex and should only be attempted if the above steps fail. It involves configuring your home router.

Find Your Router's IP Address: Open Command Prompt and type ipconfig. Look for "Default Gateway" under your active network adapter. This is your router's IP (e.g., 192.168.1.1).

Access Router Settings: Open a web browser and type your router's IP address into the URL bar. You'll need to log in (check your router's manual or a sticker on the router for default credentials).

Locate Port Forwarding: Look for sections like "Port Forwarding," "NAT," "Virtual Servers," or "Applications and Gaming."

Create a New Rule:

Service Port / External Port: Enter the port your P2P application is listening on (e.g., 52855).

Internal Port: Usually the same as the external port.

Internal IP Address: Enter your computer's private IP address (the "My Lan IP" from your P2P app, e.g., 192.168.5.7). It's best to set a static IP for your computer or use DHCP reservation on your router to prevent this IP from changing.

Protocol: Select "Both" (TCP/UDP) or "TCP" if the app primarily uses TCP.

Enable/Apply: Save or enable the rule.

Instruct the Other User: If the other user is also behind a restrictive NAT, they might need to perform port forwarding on their router as well.

Step 5: Network Stability and Application Version
Internet Connection: Ensure both users have stable internet connections.

Application Version: Make sure both users are running the exact same version of the P2P application. Incompatibilities between versions can prevent connections.

Start with Step 1 and work your way down. The most common issues are incorrect peer information and firewall blocks. Good luck!

[althakar]

HI,

I tried as you mentioned above, STUN aslo matchign version too matching, enable firewall and deactivated firewall on both system still not able to connect.

Both system has good internet connection of 100 Mbps.

I tried both system in same network and even tried virtual system in same pc but still not conencting.

[VaradGupta23]

1. Confirm Local Listening on Port
   On the system where the app is running in "listener" mode:

Open Command Prompt and run:

netstat -an | find "52855"
(Replace 52855 with the actual listening port)

If it shows LISTENING, the app is bound correctly.

If nothing is listening — the app may not be binding to the port properly.

2. Test Local TCP Loopback
   Run this test directly on the same system:

Open two terminals:

One runs a listener:

nc -l -p 52855
One sends a test message:

nc 127.0.0.1 52855
If this fails, the port cannot be bound locally, possibly due to antivirus, permissions, or Windows service restrictions.

3. Run App as Administrator
   Sometimes the app fails to bind ports due to lack of privileges.

Right-click → Run as Administrator on both systems.

4. Check for Loopback Restrictions on Windows
   Some apps can't receive from 127.0.0.1 or localhost due to Windows security restrictions.

Run this PowerShell command:

CheckNetIsolation LoopbackExempt -s
If your app is not listed, add it:

CheckNetIsolation LoopbackExempt -a -n="YourAppPackageName"
(For UWP/Store apps only — skip if not relevant)

5. Review Logs or Console Output
   If the app has logs or outputs in console:

Check if it prints errors like:

"Bind failed"

"Permission denied"

"Failed to resolve STUN"

6. Try Manual Port Forwarding (for real WAN tests)
   You can skip this if testing only on local or virtual environments, but for real internet use, make sure:

Port forwarding is active

STUN resolves correct public IP and NAT type

No carrier-grade NAT

Suggestion (if you built the app or have code access)
Print connection state: show if socket.bind() or listen() failed.

Check if app supports logs or debug mode.

Let me know what happens when:

You run netstat to confirm port binding

You try local TCP test via nc or similar tool

You run the app as administrator

Once we confirm it's actually binding and accepting on the expected port, we can go further.

[althakar]

Hi Varad,

Port was not pinging internally, now I have open all the ports in firewall and its working internally. but I am worried when all ports are open , any app can excess my system.

Is there any way where we can set the port for this app?

Below are the tests I have done.

1.Confirm Local Listening on Port

2.Test Local TCP Loopback
One runs a listener:

One sends a test message:

3.Run App as Administrator
Tried but no luck

4. Check for Loopback Restrictions on Windows
   CheckNetIsolation LoopbackExempt -s

5. Review Logs or Console Output
   I cant find any logs to view

[VaradGupta23]

Issue Recap
You managed to get internal connections working only after opening all ports in the firewall. Now you're worried (rightly) about security.

Solution: Open Only a Specific Port
Yes — you absolutely should not leave all ports open. It’s risky and unnecessary. Instead, follow these secure steps to allow only the specific port your app needs:

Step-by-Step: Allow Specific Port in Windows Firewall

1. Choose a Fixed Port
   Let’s say your app will always use port 52855 (or choose any available port).

2. Close All Ports Again
   Go to Windows Defender Firewall settings.

Make sure “Block all incoming connections” is selected (except those you explicitly allow).

Remove any rule that was allowing “All Ports” or “All Apps”.

3. Create a New Rule to Open Only Your App's Port
   Open Windows Defender Firewall with Advanced Security.

On the left pane, click on Inbound Rules → then New Rule…

Choose Port, click Next.

Select TCP (or UDP if your app uses it — usually TCP).

Enter Specific local ports: 52855 → click Next.

Select Allow the connection.

Apply it to Private and/or Public, depending on your network.

Give it a name like "MyP2PApp-Inbound-TCP-52855".
Repeat the same for Outbound Rule if needed (usually not needed unless the app sends on a specific port).

Optional (But Ideal): Bind Your App to a Specific Port
If your app doesn’t allow configuring the port from the UI, but you have access to the code, update it to bind to a constant port like so:

Node.js example:

server.listen(52855, () => {
console.log("Listening on port 52855");
});
C++ example:

bind(sock, (struct sockaddr*)&addr, sizeof(addr)); // where addr.sin_port = htons(52855);
Let me know what language or framework you’re using — I can give exact code for setting the port.

Verify It's Secure
Use netstat -an | find "52855" to verify it’s listening on only that port.

Use online port scanner (like yougetsignal) to check only 52855 is exposed — nothing else.

Run nmap from another machine to double-check.

Bonus: If Using STUN/TURN
Make sure your app:

Uses the STUN result to determine its public IP.

Advertises port 52855 in its peer connection handshake.

Doesn't randomize ports each time it starts.