My Technical Blog

Many of us used BitTorrent(or uTorrent) to download files on internet in a short time. Their download speed is high due to Peer-to-peer technology. That means, rather than downloading file from server, we are getting the file from another computer. But how two computers that have a local IP and are behind NAT, how they can connect each other? For that, NAT Traversal methodologies come for help. Note that there are mainly 2 types of NAT: Symmetrical(complex NATs:carrier-grade NAT) and Full (home network or small enterprises). let us consider Full NATs first. Methodologies of NAT traversal are: UPnP - old and hardware oriented method NAT-PMP (later succeeded by PCP)- introduced by Apple, also hardware oriented(i.e: not all routers have it, and even if it had, it is turned off by default) UDP Punching  - this is done by STUN which uses public server to discover NAT public IP & port TCP Punching -  similar to UDP punching but more complicated Symmetrical NATs are...

Recently, I have been interested in sniffing Http requests/responses which are passing through 80/8080 port. This is helpful when you want to trace if there are some data outgoing from your PC without your knowledge. Sniffing(or monitoring) is a popular way to observe http requests. Anyways, I decided to choose Python for programming, because it is easier, portable, and extensible. There are tons of libraries for Python. The next library that i want to introduce is called "scapy" You install it like this: >pip install scapy Then, here is the simple HTTP sniffer: #!/usr/bin/python from scapy.all import * def http_header(packet):         http_packet=str(packet)         if http_packet.find('GET'):                 return GET_print(packet) def GET_print(packet1):     ret = "***************************************GET PACKET****************************************************\n" ...