Windows Server 2008 inherits the TCP/IP stack limitations from Windows networking architecture. The 65,536 (2^16) theoretical maximum comes from:

• 16-bit port addressing (0-65535)
• Default dynamic port range (49152-65535)
• System-reserved ports below 1024

However, the actual usable connection count depends on several factors:

netsh int ipv4 show dynamicport tcp
// Typical output: Start Port: 49152, Number of Ports: 16384

For Comet applications requiring massive concurrent connections, consider these optimizations:

1. Expanding Ephemeral Port Range

netsh int ipv4 set dynamicport tcp start=1025 num=64511
// This makes ports 1025-65535 available for outbound connections

2. Leveraging Multiple IP Addresses

Each additional IP address provides another 65K potential connections:

// C# example binding to specific local endpoint
var listener = new TcpListener(new IPEndPoint(IPAddress.Parse("192.168.1.100"), 0));

3. Tuning TCP Stack Parameters

// Registry tweaks for high-concurrency scenarios
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"MaxUserPort"=dword:0000fffe
"TcpTimedWaitDelay"=dword:0000001e
"MaxFreeTcbs"=dword:00002000

When implementing C# Comet servers:

• Use async I/O patterns (BeginAccept/EndAccept)
• Implement connection pooling
• Consider IOCP (I/O Completion Ports) for scalability

// Async TCP server skeleton in C#
public class AsyncTcpServer {
    private TcpListener _listener;
    
    public void Start() {
        _listener = new TcpListener(IPAddress.Any, 8080);
        _listener.Start();
        _listener.BeginAcceptTcpClient(AcceptCallback, null);
    }
    
    private void AcceptCallback(IAsyncResult ar) {
        var client = _listener.EndAcceptTcpClient(ar);
        // Handle client connection
        _listener.BeginAcceptTcpClient(AcceptCallback, null);
    }
}

For extreme scenarios (>100K connections):

• Consider Windows Server 2008 R2 (improved TCP stack)
• Evaluate third-party TCP stacks like Winsock Direct
• Implement port multiplexing at application layer

The fundamental constraint in Windows Server 2008 stems from TCP port exhaustion. Each TCP connection requires a unique (source IP, source port, destination IP, destination port) tuple. With a single IP address, you're theoretically limited to ~65K outgoing connections due to the 16-bit port range (0-65535), minus the reserved ports below 1024.

To surpass this limit, we need multiple IP addresses on the server NIC. Windows Server 2008 can handle this through:

• Multiple physical NICs (less practical)
• Virtual IP addresses on a single NIC (recommended)
• IPv6 implementation (though client compatibility may vary)

// C# example for binding to specific local endpoints
var listener = new TcpListener(IPAddress.Any, 8080);
// Alternative for multiple IPs:
var endpoints = new[]
{
    new IPEndPoint(IPAddress.Parse("192.168.1.100"), 8080),
    new IPEndPoint(IPAddress.Parse("192.168.1.101"), 8080)
};

Modify these registry settings (reboot required):

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"MaxUserPort"=dword:0000fffe
"TcpTimedWaitDelay"=dword:0000001e
"TcpNumConnections"=dword:00fffffe

With 10 virtual IPs (10.x.x.1 through 10.x.x.10):

// Pseudo-code for connection handling
async Task HandleCometConnections()
{
    var tasks = new List();
    foreach (var ip in virtualIPs)
    {
        tasks.Add(RunListenerOnIP(ip));
    }
    await Task.WhenAll(tasks);
}

Essential counters to watch:

• TCPv4/Connections Established
• TCPv4/Connection Failures
• Memory/Available Bytes
• System/Context Switches/sec

For extreme scenarios (>500K connections):

1. Implement connection pooling
2. Use UDP with application-layer reliability
3. Consider WebSockets for more efficient protocols