You can get a good overview of the differences between IPv4 and IPv6
policies regarding IP address assignments and the registration process of
obtaining IP addresses at www.arin.net/knowledge/v4-v6.html and
http://www.arin.net/resources/request.html.
Ubuntu, like all other modern Linux distributions, supports the use of IPv6
and includes a number of networking tools that conform to IPv6
addressing.
Migration to IPv6 is slow in coming, however, because many computer
operating systems, software, hardware, firmware, and users are still in the
IPv4 mindset. Supporting IPv6 requires rewriting many networking
utilities, portions of operating systems currently in use, and firmware in
routing and firewall hardware.
See the “IPv6 Basics” section, later in this chapter, for more on IPv6.Using IP Masquerading in Ubuntu
Three blocks of IP addresses are reserved for use on internal networks and
hosts not directly connected to the Internet. The address ranges are from
10.0.0.0 to 10.255.255.255, or 1 Class A network; from 172.16.0.0 to
172.31.255.255, or 16 Class B networks; and from 192.168.0.0 to
192.168.255.255, or 256 Class C networks. Use these IP addresses when
building a LAN for your business or home. Which class you choose can
depend on the number of hosts on your network.
Internet access for your internal network can be provided by another PC or a
router. The host or device is connected to the Internet and is used as an
Internet gateway to forward information to and from your LAN. The host
should also be used as a firewall to protect your network from malicious data
and users while functioning as an Internet gateway.
A PC used in this fashion typically has at least two network interfaces. One is
connected to the Internet and the other is connected to the computers on the
LAN (via a hub or switch). Some broadband devices also incorporate four or
more switching network interfaces. Data is then passed between the LAN and
the Internet via NAT, sometimes known in networking circles as IP
masquerading.
NOTE
Do not rely on a single point of protection for your LAN, especially if you
use wireless networking, provide dial-in services, or allow mobile (laptop
or PDA) users internal or external access to your network. Companies,