&gt; I actually played a bit with the code and found out that exactly half of the<br />&gt; times the write() call in the function<br />&gt; gsmtap_fd_cb() (gsmtap_util.c) fails because of EAGAIN or EWOULDBLOCK.<br /><br />That&#39;s because of what Alex said.<br />If you do what he described, the port unreachable will not happen and all write will succeed.<br /><br />Cheers,<br /><br />     Sylvain