Watchguard Firebox X20E Reference Manual page 67

Internet address class
To efficiently administer the 32-bit IP address class space, IP addresses are
separated into three classes that describe networks of varying sizes:
Class AIIf the first octet of an IP address is less than 128, it is a Class A
address. A network with a Class A address can have up to about 16 million
hosts.
Class B If the first octet of an IP address is from 128 to 191, it is a Class B
address. A network with a Class B address can have up to 64,000 hosts.
Class C If the first octet of an IP address is from 192 to 223, it is a Class C
address. A network with a Class C address can have up to 254 hosts.
intranet
A self-contained network that uses the same communications protocols and
file formats as the Internet.
IP (Internet Protocol)
A protocol used by the Internet that enables computers to communicate over
various physical media.
IP address host
The 32-bit address that identifies a host. Technically, a host is a network
device connected to the Internet. In common usage, a host is a computer or
some other device that has a unique IP address. Computers with more than
one IP address are known as multihomed hosts.
IP fragment
An IP datagram that is actually part of a larger IP packet. IP fragments are
typically used when an IP packet is too large for the physical media that the
data must cross. For example, the IP standard for Ethernet limits IP packets to
about 1,500 bytes, but the maximum IP packet size is 65,536 bytes. To send
packets larger than 1,500 bytes over an Ethernet, IP fragments must be used.
IP masquerading
See dynamic NAT.
IP options
Extensions to the Internet Protocol used mainly for debugging and special
applications on local networks. In general, there are no legitimate uses of IP
options over an Internet connection.
IPSec (Internet Protocol Security)
An open-standard methodology of creating a secure tunnel through the
Internet, connecting two remote hosts or networks. IPSec provides several
encryption and authentication options to maximize the security of the
transmission over a public medium such as the Internet.
ISP (Internet service provider)
Typically, a business that sells access to the Internet. A government
organization or an educational institution may be the ISP for some
organizations.
Reference Guide 63