~$ sudo netcat -l -v 7

inet addr:172.17.9.71
Bcast:172.17.11.255
Mask:255.255.252.0

inet addr:172.17.9.165
Bcast:172.17.11.255
Mask:255.255.252.0

LWIP_HAVE_LOOPIF = 0
LWIP_HAVE_LOOPIF = 0
tcp_bind: bind to port 55555
tcp_connect to port 7
netif_default =  -780756800
netif_is_up(netif_default) =  0
ip_route: No route to 172.17.9.71
connect err =  -4
netif_default =  -780756800
netif_is_up(netif_default) =  0
ip_route: No route to 172.17.9.71
ip_output: No route to 172.17.9.71
Assertion "mem_free: mem->used" failed at line 339 in ../../../../../lwip/src/core/mem.c

const char *helloworld = "hello world\n";



void hello_end(struct tcp_pcb *pcb, u8_t *state)
{
tcp_err(pcb, NULL);
tcp_recv(pcb, NULL);
tcp_sent(pcb, NULL);
tcp_poll(pcb, NULL, 0);
mem_free(state);
}
err_t hello_recv(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
{
u8_t *state = (u8_t *)arg;
u16_t len;

if (p == NULL)
if (*state == 255) /* close send */
hello_end(pcb, state);
else /* close not yet send */
*state |= 2;
else
{
len = p->tot_len;
pbuf_free(p);
tcp_recved(pcb, len);
}

return ERR_OK;
}

void hello_err(void *arg, err_t err)
{
mem_free(arg);
}

err_t hello_poll_close(void *arg, struct tcp_pcb *pcb)
{
u8_t *state = (u8_t *)arg;

if (tcp_close(pcb) == ERR_OK)
{
if ((*state & 2) == 2) /* close received */
hello_end(pcb, state);
else /* close not yet received */
*state = 255;
}

return ERR_OK;
}

err_t hello_connected(void *arg, struct tcp_pcb *pcb, err_t err)
{
tcp_write(pcb, helloworld, 12, 0);
return ERR_OK;
}

err_t hello_connect() {

        lwip_init();
        u8_t *state;
        err_t err;
        struct tcp_pcb *pcb;
        ip_addr_t ipaddr;

          IP4_ADDR(&ipaddr, 172,17,9,71);
          if ((state = mem_malloc(1)) == NULL)  {
             return ERR_MEM;
          }
        
           *state = 1;
           if ((pcb = tcp_new()) == NULL)  {
           mem_free(state);
           return ERR_MEM;
          }

          tcp_arg(pcb, state);
          tcp_err(pcb, hello_err);
          tcp_recv(pcb, hello_recv);
          tcp_sent(pcb, NULL);
          tcp_poll(pcb, hello_poll_close, 10);





          tcp_bind(pcb,IPADDR_ANY, 55555); //Bind ourselvs to the port 55555 and my own adress


          err = tcp_connect(pcb, &ipaddr, 7, hello_connected);
          if (err != ERR_OK)  {
             std::cout << "connect err =  " << (int)err << std::endl;
            mem_free(state);
             tcp_abort(pcb);
        }

          getchar();
          return ERR_OK;
}

int main(int argc, char** argv) {

         err_t err =  hello_connect();
           if (err != ERR_OK)  {
           std::cout << "2err =  " << err << std::endl;
           }
            std::cout << "End of Main" << std::endl;
            return 0;


        return 0;
}

tap0      Link encap:Ethernet  HWaddr 86:97:2c:64:b7:78  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::8497:2cff:fe64:b778/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:33 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:0 (0.0 B)  TX bytes:6555 (6.4 KiB)

char *eth = "eht1";
  netif_set_default(netif_find(eth));

LWIP_HAVE_LOOPIF = 0
LWIP_HAVE_LOOPIF = 0
tcpip_thread: PACKET 0x7f72acaa1988
ip_input: packet not for us.
tcp_bind: bind to port 55555
tcp_connect to port 7
netif_default =  0

err = tcp_connect(pcb, &ipaddr, 7, hello_connected);