C++
C++
Socket Connect Failure Cases
See more Socket/SSL/TLS Examples
Demonstrates a few common situations that would cause a TCP connect to a remote host:port to fail, an examines the LastErrorText for each case.This example discusses the following cases:
- The remote host is not listening on the desired port.
- No remote host exists at the IP address (such as on a LAN).
- The local Windows Firewall blocks the outbound connection.
- Your ISP blocks the outbound connection.
- The remote Windows Firewall blocks the inbound connection.
- The domain cannot be resolved to an IP address.
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#include <CkSocket.h>
void ChilkatSample(void)
{
bool success = false;
// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.
CkSocket socket;
bool tls = false;
int maxWaitMillisec = 5000;
// First test the case where the remote host is not listening on the desired port.
// In this case, my LAN has a computer at 192.168.1.137, but nothing on that computer
// is listening for inbound connection to port 6660.
success = socket.Connect("192.168.1.137",6660,tls,maxWaitMillisec);
std::cout << socket.lastErrorText() << "\r\n";
// The call to Connect should fail quickly, and the LastErrorText will contain
// a message about the connection being rejected:
//
// socket2Connect:
// connect2:
// ConnectFailReason: Connection rejected
// --connect2
// --socket2Connect
// Now test the case where there is no computer on the network at the desired IP address.
// For example, on my LAN, there is no computer at 192.168.1.188. If ping is used to test,
// the error message would be "Destination host unreachable".
success = socket.Connect("192.168.1.188",80,tls,maxWaitMillisec);
std::cout << socket.lastErrorText() << "\r\n";
// In this case, the connection is "rejected" as before, but the connect hangs for the entire
// maximum waiting period (maxWaitMillisec), which is 5 seconds in this case.
// (If the maxWaitMillisec is a large enough amount of time, the operating system
// may fail the connect with a "connection rejected" after a long wait.
// The difference is that when the remote host exists and is reachable, the failure is quick.)
// The portion of the LastErrorText for this failure is shown here:
// connectInner:
// hostname: 192.168.1.188
// port: 80
// tls: 0
// maxWaitMs: 5000
// socket2Connect:
// connect2:
// connectSocket:
// connect_ipv6_or_ipv4:
// timeout waiting for connect to complete
// numSec: 5
// numMicroSec: 0
// failedWaitToConnect: Socket operation timeout.
// --connect_ipv6_or_ipv4
// --connectSocket
// ConnectFailReason: Timeout
// --connect2
// --socket2Connect
// Failed.
// --connectInner
// Imagine that a new rule is added to Windows Firewall to block all connections
// for this example app. The characteristics of the failure are the same as for
// the case where nothing on the remote computer is listening at the given port.
// The connection attempt fails immediately, and the error message (from the OS) is
// "connection rejected". Also notice that SSL/TLS never enters the equation because
// the SSL/TLS handshake begins *after* the TCP connection is completed. When the
// TCP connection fails, it never reaches the point of even beginning the SSL/TLS negotiation.
tls = true;
success = socket.Connect("192.168.1.188",80,tls,maxWaitMillisec);
std::cout << socket.lastErrorText() << "\r\n";
// connectInner:
// hostname: smtp.gmail.com
// port: 465
// tls: 1
// maxWaitMs: 5000
// socket2Connect:
// connect2:
// ConnectFailReason: Connection rejected
// --connect2
// --socket2Connect
// Failed.
// --connectInner
// What about the case where the ISP blocks an outbound connection? My home ISP is
// Comcast cable, and they block outbound SMTP port 25.
tls = false;
success = socket.Connect("pop3.btconnect.com",25,tls,maxWaitMillisec);
std::cout << socket.lastErrorText() << "\r\n";
// The result is a timeout:
// connectInner:
// hostname: pop3.btconnect.com
// port: 25
// tls: 0
// maxWaitMs: 5000
// socket2Connect:
// connect2:
// connectSocket:
// connect_ipv6_or_ipv4:
// timeout waiting for connect to complete
// numSec: 5
// numMicroSec: 0
// failedWaitToConnect: Socket operation timeout.
// --connect_ipv6_or_ipv4
// --connectSocket
// ConnectFailReason: Timeout
// --connect2
// --socket2Connect
// Failed.
// --connectInner
// What about the case where the Windows Firewall at the remote host is blocking the
// inbound connection. On Chilkat's internal LAN, there is a computer at 192.168.1.127
// running an SSH server. After adding an inbound rule to block port 22, external connections
// fail with a timeout, as shown below:
success = socket.Connect("192.168.1.127",22,tls,maxWaitMillisec);
std::cout << socket.lastErrorText() << "\r\n";
// connectInner:
// hostname: 192.168.1.127
// port: 22
// tls: 0
// maxWaitMs: 5000
// socket2Connect:
// connect2:
// connectSocket:
// connect_ipv6_or_ipv4:
// timeout waiting for connect to complete
// numSec: 5
// numMicroSec: 0
// failedWaitToConnect: Socket operation timeout.
// --connect_ipv6_or_ipv4
// --connectSocket
// ConnectFailReason: Timeout
// --connect2
// --socket2Connect
// Failed.
// --connectInner
// Finally, what if we try to connect to a hostname that does not resolve to an IP address?
success = socket.Connect("www.thisdoesnotresolvetoanyipaddressxyz.com",22,tls,maxWaitMillisec);
std::cout << socket.lastErrorText() << "\r\n";
// In this case there is an immediate failure:
// connectInner:
// hostname: www.thisdoesnotresolvetoanyipaddressxyz.com
// port: 22
// tls: 0
// maxWaitMs: 5000
// socket2Connect:
// connect2:
// connectSocket:
// connect_ipv6_or_ipv4:
// resolveHostname6:
// getAddressInfo:
// Failed to get host address info. (3)
// SocketError: WSAHOST_NOT_FOUND No such host is known.
// hostOrIpAddr: www.thisdoesnotresolvetoanyipaddressxyz.com
// port: 22
// Versions of Windows earlier than Windows XP are limited to handling IPv4 only
// On Windows Server 2003 and Windows XP, IPv6 addresses are returned only if IPv6 is installed on the local computer.
// --getAddressInfo
// --resolveHostname6
// Domain to IP address resolution failed.
// --connect_ipv6_or_ipv4
// --connectSocket
// ConnectFailReason: DNS lookup failed
// --connect2
// --socket2Connect
// Failed.
// --connectInne
}