You didn't really expect to learn how to hack without knowing the past, did you? A military commander studies past military engagements and evaluates them. So we must study internet history and learn from it.

 Do we really need to know the past? In a word, yes. The internet isn't that old. Its still in its infacy so think yourself luck you only gotta go through a few years and pity the fool who starts hacking 100 years into internet evolution! Why do we need to learn internet history? Because it gives us a greater understanding of the systems and evolution of those systems and where the vulnerabilities might lie.

 So do dive in a great place to start is with RFC 760.  The full document can be found here:

http://tools.ietf.org/rfc/rfc760.txt

RFC 760 is an overview of the early internet and if your not familiar with it, get reading. It'll give you a basic understanding of what the more technical side of the internet entails -  rather than the graphically designed front end that we all use. If you want to get serious about hacking and security, its all in the engine of the interent. That means using command line interfaces and getting dirty with code. 

RFC 760 deals very much with the Internet Protocol and its functions. Its an essential part of serious hacking (as opposed to script kiddies) that you understand how the internet protocol works - its packaging and sending of datagrams, fragmentation of datagrams and identification and assmebly of fragmented datagrams.

If you wish to follow whats going on below, its advisable that you read RFC 760 at the link above.

Headers are the central part in organising the data flow both within the internet and at the source and destination addresses. A typical Header has the following fields (some have sub-fields)

• version
• IHL
• Type of Service
• Total Length
• Identification
• Flags
• Fragment Offset
• Source Address
• Destination Address
• Options
• Padding

All the options above are explained in RFC760.

Dealing with Fragments is one particular section you should read and get a handle on. Packets (eg. pictures, files, emails) sent over the internet are fragmented if they exceed the MTU setting (Maximum Transfer Unit). Sniffing on networks can result in fragments being intercepted and its important to know the sequence and background of assembling the completed package.

To quote directly from RFC760, sending and receiving headers is carried out in the following format:

The following two calls satisfy the requirements for the
  user to internet protocol module communication ("=>" means returns):

    SEND (dest, TOS, TTL, BufPTR, len, Id, DF, options => result)

      where:

        dest = destination address
        TOS = type of service
        TTL = time to live
        BufPTR = buffer pointer
        len = length of buffer
        Id  = Identifier
        DF = Don't Fragment
        options = option data
        result = response
          OK = datagram sent ok
          Error = error in arguments or local network error

    RECV (BufPTR => result, source, dest, prot, TOS, len)

      where:

        BufPTR = buffer pointer
        result = response
          OK = datagram received ok
          Error = error in arguments
        source = source address
        dest = destination address
        prot = protocol
        TOS = type of service
        len = length of buffer

  When the user sends a datagram, it executes the SEND call supplying
  all the arguments.  The internet protocol module, on receiving this
  call, checks the arguments and prepares and sends the message.  If the
  arguments are good and the datagram is accepted by the local network,
  the call returns successfully.  If either the arguments are bad, or
  the datagram is not accepted by the local network, the call returns
  unsuccessfully.  On unsuccessful returns, a reasonable report should
  be made as to the cause of the problem, but the details of such
  reports are up to individual implementations.

 

 It might look like gobbledygook at the moment but as you progress in hacking the importance of the above and your understanding of it will become clear.