Detecting an internet connection.

**jase jennings** · July 30th, 2003, 06:26 PM

Hi

My application connects to the internet to check for updates.

It does so using functions in ras32.dll (RasGetConnectStatus)
If ras32.dll does not exist, I use win inet functions (CInternetSession::OpenURL)

Two problems :

1. If not connected, the wininet functions take a while to time out. I always call it in a thread which i timeout after 5 seconds, but still it's not perfect.

2. RAS functions only work when an internet dialup is present. If you have cable modem / router / lan, RAS will always return "not connected", even if you are.

I read a newsgroup posting from a microsoft guy who suggested also using IsNetworkAlive() and IsDestinationReachable(), but both of those fail for me, regardless of connection state.

I have writtten a class which works well for dialup connection. But in the case of "always on" connections, I have yet to find a good method for detection of internet availability.

Any suggestions guys ?

Jase

**kuphryn** · July 31st, 2003, 12:53 AM

Winsock WSAConnect() sometimes takes five or more seconds to before returning. One solution is to manually close the socket. Thus, as for your question there is no solution.

Kuphryn

**jase jennings** · July 31st, 2003, 02:49 AM

There must be a way. How do internet browsers know whether or not you are connected to the net ? There absolutley has to be a fool proof way, and it's probably undocumented ...

Jase

**kochhar** · July 31st, 2003, 10:14 AM

I've been using the following function with success. It returns
TRUE if a connection is available, and takes less than
a sec in either case:

Code:

BOOL Online()
{
    DWORD dwState = 0; 
    DWORD dwSize = sizeof(DWORD);
	 return InternetQueryOption(NULL,
		 INTERNET_OPTION_CONNECTED_STATE, &dwState, &dwSize)
		 && (dwState & INTERNET_STATE_CONNECTED);
}

Credit: I got this from Paul Dilascia's column in MSDN mag a while
back.

**kmashif** · September 10th, 2004, 12:24 AM

The online function always return true though i am working in offline. Please tell me what is problem. I aam connected to Internet by LAN.

Originally Posted by kochhar

I've been using the following function with success. It returns
TRUE if a connection is available, and takes less than
a sec in either case:

Code:

BOOL Online()
{
    DWORD dwState = 0; 
    DWORD dwSize = sizeof(DWORD);
	 return InternetQueryOption(NULL,
		 INTERNET_OPTION_CONNECTED_STATE, &dwState, &dwSize)
		 && (dwState & INTERNET_STATE_CONNECTED);
}

Credit: I got this from Paul Dilascia's column in MSDN mag a while
back.

**DennisOlly** · March 2nd, 2005, 07:44 AM

Hi,

ran into this problem of having to detect the presence of an internet connection, found this thread and decided to post my VERY unsatisfying, but working, 'solution'. Especially the part where it needs a batch file is extremely annoying.
Moreover, as discussed in this thread, this 'solution' obviously doesn't work from behind routers that disabled pinging.

cheers,
Dennis

Code:

#include <stdio.h>
#include <string.h>
#include <process.h>

int main(int argc, char* argv[])
{
    FILE *f1;
    int check;
    char fbuf[150];

    // try to ping 66.102.11.104 (www.google.nl), just ONCE, waiting for MAX 500 msec
    // batch file needed because ping doesn't take "> testIC.bat" for an argument
    check = spawnl( P_WAIT, "c:\\windows\\testIC.bat", "testIC.bat", "500", "1", 
    "66.102.11.104", "c:\\windows\\testIC.tmp", NULL );
    if( check == -1 )
        // error from spawnl
        return -1; 

    f1 = fopen( "c:\\windows\\testIC.tmp", "rb" );
    if( !f1 )
        // error opening file
        return -1; 

    // read the first 149 bytes from testIC.tmp
    fread( fbuf, 149, 1, f1 ); 
    fbuf[149] = NULL;
    fclose( f1 );
    if( strstr( fbuf, "Reply from" ) != NULL )
        // reply received, internet connection viable
        return 1;   

    // no reply received, assume internet connection lost
    return 0;    
}

testIC.bat just reads:

Code:

ping -w %1 -n %2 %3 > %4

_

**Peter Cseke** · March 2nd, 2005, 08:35 AM

You should try the DNS name resolution instead of ping (gethostbyname). That will probably not be disabled by such routers.

**jase jennings** · August 1st, 2003, 12:08 PM

Nope

It returns connected even when i'm not ...

Next !

**jase jennings** · August 4th, 2003, 10:53 AM

Bump!

Anybody ?

**kochhar** · August 4th, 2003, 07:47 PM

Originally posted by jase jennings
Nope

It returns connected even when i'm not ...

What platform are you testing this on? I tried my function
both at work (Win/XP, VS v6, ethernet (twiested pair))
and at home (Win/XP, VS v6, modem) and every time it
returned the correct answer within a second or less.

My ethernet card (actually it's built into the motherboard)
is an "Intel(R) PRO/100 VE". Maybe that makes a difference..

**jase jennings** · August 6th, 2003, 01:30 AM

> What platform are you testing this on?

XP Pro, VS.NET, Cable modem (always on)

I've no doubt your function works fine with a dial up modem, but not when you are using a router / lan

Jase

**Mick** · August 6th, 2003, 01:38 AM

Originally posted by jase jennings
> What platform are you testing this on?

XP Pro, VS.NET, Cable modem (always on)

I've no doubt your function works fine with a dial up modem, but not when you are using a router / lan

Jase

I assume you just want to check connectivity, so if you want a fast time out. Ping the destination first.

**jase jennings** · August 6th, 2003, 02:43 AM

Do you have an example of a ping() function ?
I don't want to execute ping through the shell if i can help it.

**Mick** · August 6th, 2003, 02:58 AM

Originally posted by jase jennings
Do you have an example of a ping() function ?
I don't want to execute ping through the shell if i can help it.

hmm should be something like this, for a shorter condensed version.., I'll pull it outta one of my classes and see if I can shorten it into a small console app in a couple of minutes...

Code:

   HANDLE icmphandle = ::IcmpCreateFile();

	    char reply[sizeof(icmp_echo_reply)+8];

	    
	    DWORD dw = IcmpSendEcho(icmphandle,
        *((u_long*)hostinfo->h_addr_list[0]),
		    0,0,NULL,
		    reply,sizeof(icmp_echo_reply)+8,1000);
	    

	    IcmpCloseHandle(icmphandle);

        if (dw == 0)

You'll need the SDK, the ICMP files are not in the standared include/lib dirs, it's in SDK\misc\icmp\xxx

But here is a link that looks ok, for all the long winded code...

http://www.sockets.com/ms_icmp.htm

You just want to look for the Icmp calls above, on google, probably some samples on codeguru 2.

**kochhar** · August 6th, 2003, 03:01 AM

Originally posted by jase jennings
I've no doubt your function works fine with a dial up modem, but not when you are using a router / lan

I tested as follows:
(1) Ethernet cable connected: returned TRUE
(2) Disconnect cable: returnd FALSE
(3) Reconnected cable: returned TRUE

I suppose there must be cases where it fails, but I don't
know what they are or why.

I am attaching a small program that shows how to ping
from your program. Most of the code was posted by
Steve Bryndin at Codeguru. I just modified in small ways.
Note that it does a lot more than just ping a number, e.g.
you can ask it to ping by name, etc. But it works well.

Good luck.

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