title: How do I block packets coming on port 23 on my computer?
body: <p>I am using libpcap library. I have made one packet sniffer C program using pcap.h. Now I want to block packets coming on port 23 on my computer via <code>eth0</code> device. I tried pcap_filter function but it is not useful for blocking.
  Please explain to me how to code this functionality using c program.</p>