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Glossary

FortiGate-60M Administration Guide

01-28007-0144-20041217

367

MTU

Maximum Transmission Unit

: The largest

physical packet size, measured in bytes, that a network
can transmit. Any packets larger than the MTU are
divided into smaller packets before they are sent.

NAT, Network Address Translation

: A way of routing

IPv4 packets transparently. Using NAT, a router or
FortiGate unit between a private and public network
translates private IP addresses to public addresses
and the other way around.

netmask, network mask

: Also sometimes called

subnet mask. A 32-bit quantity that indicates which bits
of an IP address refer to the network portion.

NTP

Network Time Protocol

: Used to synchronize

the time of a computer to an NTP server. NTP provides
accuracies to within tens of milliseconds across the
Internet relative to coordinated universal time.

OSI, Open Systems Interconnection

: A standard that

defines network communication protocols using a
seven-layer model.

packet

: A piece of data transmitted over a packet-

switched network. A packet contains a payload, the
source and destination addresses, and a checksum. In
IP networks, packets are often called datagrams.
Packets are passed between the OSI data-link and
network layers.

PAP, Password Authentication Protocol

: An

authentication protocol supported by PPP. See also

PPP

ping, packet Internet grouper

: A utility for

determining whether the device at a specific IP address
is accessible. The utility sends a packet to the specified
address and waits for a reply.

POP3, Post Office Protocol

: A protocol used to

transfer email from a mail server to a mail client across
the Internet. Most email clients use POP.

port

: The part of an interface on which application

traffic is carried. By convention, the port number
identifies the type of traffic. For example, port 80 is
used for HTTP traffic.

PPP, Point-to-Point Protocol

: A protocol for

transmitting IP packets over serial point-to-point links
(that is, across any DTE/DCE interface).

PPPoE, PPP over Ethernet

: A protocol that specifies

how to encapsulate PPP packets over Ethernet.

PPTP, Point-to-Point Tunneling Protocol

: A security

protocol that creates a VPN by encapsulating PPP
packets.

protocol

: A standard format for transmitting data. The

protocol determines the type of error checking to be
used, the data compression method (if any), how the
sending device indicates that it has finished sending a
message, and how the receiving device indicates that it
has received a message.

RADIUS

Remote Authentication Dial-In User

Service

: A user authentication and network-usage

accounting system. When users dial into an ISP they
enter a user name and password. This information is
passed to a RADIUS server, which authenticates the
user and authorizes access to the network.

remote

: The far end point (an IP address or port

number) of a connection.

replay detection

: A way to determine whether a replay

attack is underway in an IPSec tunnel. A replay attack
occurs when an unauthorized party intercepts a series
of IPSec packets and changes them in an attempt to
flood a tunnel or access a VPN.

RFC, Request for Comments

: Internet Standards

Committee documentation.

RIP, Routing Information Protocol

: An Internet

protocol for sharing routing information within an
autonomous system.

router

: A hardware device that connects computers on

the Internet together and routes traffic between them. A
router may connect a LAN and/or DMZ to the Internet.

routing

: The process of determining which path to use

for sending packets to a destination.

routing table

: A list of possible paths that a packet can

take to reach a destination.

SA, Security Association

: SAs protect tunneled

packets. They contain the information needed to create
an IPSec VPN tunnel. An SA is uniquely identified by a
security parameter index, an IP destination address,
and a security protocol identifier. The Internet Security
Association and Key Management Protocol (ISAKMP)
is used to manage SAs.

server

: An application that answers requests from

clients. Used as a generic term for any device that
provides services to the rest of the network such as
printing, storage, and network access.