Networked Games - Game Programming Algorithms and Techniques - page 301

IP
IP, or Internet Protocol , is the base protocol that must be followed to send any
data over the Internet. Every protocol mentioned in this chapter, whether ICMP,
TCP, or UDP, must additionally follow Internet Protocol in order to transmit data.
This is even if the data is going to be transmitted over a local network. This is
due to the fact that in a modern network, all machines on a local network will be
assigned a specific local address that can be used to identify a particular local ma-
chine via IP.
The Internet Protocol header has a large number of fields, as shown in Figure 12.1 .
I won't cover what most of the elements in the header mean, but countless re-
sources online go over what each and every part of this header (and all the other
headers in this chapter) refers to.
Figure 12.1 IPv4 header.
Two versions of Internet Protocol are in wide use: v4 and v6. An IPv4 address is a
set of four 8-bit numbers (called octets ) separated by a period. So, for example, an
address on a local network might be 192.168.1.1. Because IPv4 addresses are 32
bit, there are roughly four billion possible combinations. This might have seemed
like a huge number of addresses when IPv4 was first created in 1977, but in the
modern day when even kitchen appliances connect to the Internet, four billion just
was not enough.
To combat this problem, IPv6 was developed. It uses 128-bit addresses, so it
can support an astounding 2 128 addresses. Because the addresses take up four
times the number of bytes, the IPv6 header must be different by necessity. One
downside of IPv6 addresses is they are much more difficult to memorize because
the full form is several hexadecimal numbers separated by semicolons, as in
2001:0db8:85a3:0042:1000:8a2e:0370:7334. IPv6 was officially “launched” on