false tcp connection

johnbach · 03-07-2010, 10:44 PM

Why this happens?
How to solve this?

Code:

$netstat -na |grep 9325
tcp        0      0 127.0.0.1:9325              127.0.0.1:9325              ESTABLISHED

When a client socket repeatedly tries to connect to an inactive(no server socket is listening on this port) local port,connect succeeds.
Both the endpoints(port and ip) are same

System Information

Code:

$uname -a
Linux pztest.locadomain 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux

paulsm4 · 03-07-2010, 11:50 PM

Clearly a "Ghost in the Machine"

Use "lsof" to see if you can figure out which process(es) are using the port.

If you were on Windows, and if it were udp/9325, then I might be worried. But you aren't, and it isn't - so I doubt there's any problem...

johnbach · 03-08-2010, 12:42 AM

This happens for all port(server in localhost)
I noticed this with stunnel and here is a sample c++ program to simulate it

Code:

int main(int argc, char *argv[])
{
        int sockfd, portno, n;
        struct sockaddr_in serv_addr;
        struct hostent *server;
        int stat,ctr=50000;

        char buffer[256];
        portno = 28888;
        sockfd = socket(AF_INET, SOCK_STREAM, 0);
        if (sockfd < 0)
                throw string(strerror(errno));
        server = gethostbyname(argv[1]);
        if (server == NULL)
                throw string(strerror(errno));

        bzero((char *) &serv_addr, sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr, server->h_length);
        serv_addr.sin_port = htons(portno);
        system("netstat -nap |grep 28888");

        while(ctr--)
                if ( (stat=connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr))) < 0)
                        ;//retry
                else
                {
                        cout<<"Connected ,stat="<<stat<<",ctr="<<ctr<<", Error:"<<strerror(errno)<<";";
                        system("netstat -nap |grep 28888");
                        break;
                }
}

and the output

Code:

$./a.out localhost
tcp        0      0 127.0.0.1:28888             127.0.0.1:28888             ESTABLISHED 11099/a.out
Connected ,stat=0,ctr=36047, Error:Connection refused;