I’m using a USB->Ethernet adapter, so this shouldn’t have to do with the wifi ARP issues discussed earlier.
I have a piece of software that runs on the dragonboard and listens for incoming TCP connections. Client software running on another machine connects to the IP:port and can pull off data. This software works fine on other machines, clients can connect and get data, etc. On the dragonboard the server starts up fine, but as soon as the first client tries to connect, I get the following output in /var/log/messages, kern.log, and syslog, and the connection times out:
Jun 3 17:45:44 hostname kernel: [ 39.183685] TCP: request_sock_TCP: Possible SYN flooding on port 3490. Dropping request. Check SNMP counters.
Where 3490 is the listening port of the code. It doesn’t seem to matter what port I choose, I always get that message with the applicable port number, and the client connection times out. Is there some default sysctl setting that could be causing this? Even trying to connect to the port with telnet triggers the error and subsequent timeout.
An example C++ server code that shows the problem is below:
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
int fd = -1;
int sock = socket(AF_INET, SOCK_STREAM, 0);
if(sock<0){
printf("could not open server socket");
return -1;
}
struct sockaddr_in addr;
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(3490);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sock, (struct sockaddr *) &addr, sizeof(addr))<0){
printf("could not bind server socket");
return -1;
}
if(listen(sock, 0)<0){
printf("could not listen on server socket");
return -1;
}
fd = ::accept(sock, NULL, NULL);
printf("accepted a connection: %d\n",fd);
return 0;
}
