The default TCP connect timeout in Windows isn't explicitly defined as a single fixed value - it's determined by the operating system's retransmission algorithm. Windows uses an adaptive timeout mechanism based on the TCP/IP implementation in the networking stack.

Windows calculates the initial timeout using this formula:

InitialTimeout = min(2 seconds, max(1 second, (RTT + 4 * RTTVAR) * 2))

Where RTT is the round-trip time and RTTVAR is the round-trip time variation. The maximum timeout is typically 21 seconds (after several retransmissions).

While the timeout is dynamic, you can modify some TCP parameters via registry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
    - TcpMaxConnectRetransmissions (DWORD)
    - TcpInitialRTT (DWORD)
    - TcpMaxDataRetransmissions (DWORD)

Here's how to set a custom timeout in your application code:

using System;
using System.Net.Sockets;

public class TcpClientWithTimeout
{
    public static void Connect(string host, int port, int timeout)
    {
        TcpClient client = new TcpClient();
        IAsyncResult result = client.BeginConnect(host, port, null, null);
        bool success = result.AsyncWaitHandle.WaitOne(timeout, true);
        
        if (!success || !client.Connected)
        {
            client.Close();
            throw new SocketException(10060); // Connection timed out
        }
        
        client.EndConnect(result);
        // Continue with your operations
    }
}

To modify TCP parameters programmatically:

$tcpParamsPath = "HKLM:\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters"
New-ItemProperty -Path $tcpParamsPath -Name "TcpMaxConnectRetransmissions" -Value 5 -PropertyType DWORD -Force
New-ItemProperty -Path $tcpParamsPath -Name "TcpInitialRTT" -Value 3000 -PropertyType DWORD -Force

1. Modifying these values affects all TCP connections system-wide
2. Incorrect values may degrade network performance
3. Always back up the registry before making changes
4. Consider application-level timeouts before modifying system settings

The default TCP connect timeout in Windows is determined by the system's TCP/IP stack implementation. In most modern Windows versions (Windows 7 and later), the default timeout follows this pattern:

Initial SYN retransmission: 3 seconds
Subsequent retransmissions with exponential backoff:
- Second attempt: 6 seconds
- Third attempt: 12 seconds
- Fourth attempt: 24 seconds
Total timeout before failure: ~21 seconds (sum of all retransmission intervals)

Windows provides registry settings to modify this behavior. The key parameters are located under:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

Important values include:

TcpMaxConnectRetransmissions (DWORD)
Default: 2 (Windows 10/11), meaning 3 total attempts (initial + 2 retransmissions)

TcpInitialRtt (DWORD)
Default: 3000 (3 seconds for initial SYN retransmission)

The actual timeout can vary due to:

• Network conditions (packet loss, congestion)
• Application-level timeout settings
• Windows version and updates

C# socket connection with custom timeout:

using System;
using System.Net.Sockets;

public class TcpClientWithTimeout
{
    public static void Connect(string host, int port, int timeout)
    {
        TcpClient client = new TcpClient();
        IAsyncResult result = client.BeginConnect(host, port, null, null);
        bool success = result.AsyncWaitHandle.WaitOne(timeout * 1000);
        
        if (!success || !client.Connected)
        {
            client.Close();
            throw new SocketException(10060); // Connection timed out
        }
        
        client.EndConnect(result);
        // Connection successful
    }
}

PowerShell script to modify registry settings:

# Set TCP connection timeout parameters
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters" 
    -Name "TcpMaxConnectRetransmissions" -Value 4

Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters" 
    -Name "TcpInitialRtt" -Value 1000  # 1 second initial timeout

• Prefer application-level timeouts over system-wide registry changes
• Test changes in non-production environments first
• Document any system modifications for maintenance purposes
• Consider using Windows Group Policy for enterprise deployments