DNS query tracing

dig @dns.server target.dns +tracing

watch it under wireshark, It is very useful to understand how DNS query works especially for a non-cached look up.

• As a DNS client, dig will send a standard DNS query to the target DNS server via UDP port 53. 
• For a non-cached look up, dig will ask the answer from root server, TLD (Top Level Domain) server, specific domain server in that order.

Packet crafting and sniffing with Python extensions

• libpcap: sudo apt-get install libpcap-dev

• download and install pypcap, dpkt, dnet
• pypcap 's installation is tricky: download the pyrex and recompile the pcap.pyx file will work. Furthermore, use Makefile instead of setup.py seems fixed issues.