IPv6 is the successor to the wildly successful IPv4 Internet Protocol. This section provides a quick reference to some header formats and other important features of IPv6 that are useful as reference material while perusing the main body of this book.
Figure A.1 shows an IPv6 header in graphical form. The form has been chosen to emphasize the new focus of IPv6 on 64-bit wide data structures.
The most relevant documentation for Internet standards is in the form of RFCs, a 40-yearold series of documents traditionally exchanged as ASCII line printer format pages. The column width of these documents is limited to 72 characters, making it hard to represent 64-bit wide data structures in ASCII art. The traditional way to represent packet structures in RFCs therefore limits itself to rows of 32 bits, yielding ASCII art that looks like Figure A.2.
Each tick mark represents one bit position. The numbers at the top count the bits from bit 0, the most significant bit in the first byte (generally the most significant byte as most Internet protocols use network byte order) to bit 31, the least significant bit in the fourth byte. (Note that the 0/1/2/3 above the numbers line are the digits for the tens, they don’t indicate byte boundaries!)
This notation, sometimes affectionately called ...