59.2. Network Byte Order

IP addresses and port numbers are integer values. One problem we encounter when passing these values across a network is that different hardware architectures store the bytes of a multibyte integer in different orders. As shown in Figure 59-1, architectures that store integers with the most significant byte first (i.e., at the lowest memory address) are termed big endian; those that store the least significant byte first are termed little endian. (The terms derive from Jonathan Swift’s 1726 satirical novel Gulliver’s Travels, in which the terms refer to opposing political factions who open their boiled eggs at opposite ends.) The most notable example of a little-endian architecture is x86. (Digital’s VAX architecture was another historically important example, since BSD was widely used on that machine.) Most other architectures are big endian. A few hardware architectures are switchable between the two formats. The byte ordering used on a particular machine is called the host byte order.