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Netmask : Also called subnet mask. A set of rules for omitting parts of a complete IP address to reach a target
destination without using a broadcast message. It can indicate a subnetwork portion of a larger network in
TCP/IP. Sometimes referred to as an Address Mask.
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 (UTC).
Packet : A piece of a message transmitted over a packet-switching network. One of the key features of a
packet is that it contains the destination address in addition to the data. In IP networks, packets are often
called datagrams.
Ping, Packet Internet Grouper : A utility used to determine whether a specific IP address is accessible. It
works by sending a packet to the specified address and waiting for a reply.
POP3, Post Office Protocol : A protocol used to transfer e-mail from a mail server to a mail client across the
Internet. Most e-mail clients use POP.
PPP, Point-to-Point Protocol : A TCP/IP protocol that provides host-to-network and router-to-router
connections.
PPTP, Point-to-Point Tunneling Protocol : A Windows-based technology for creating VPNs. PPTP is
supported by Windows 98, 2000, and XP. To create a PPTP VPN, your ISP's routers must support PPTP.
Port : In TCP/IP and UDP networks, a port is an endpoint to a logical connection. The port number identifies
what type of port it is. For example, port 80 is used for HTTP traffic.
Protocol : An agreed-upon format for transmitting data between two devices. 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 : An authentication and accounting system used by
many Internet Service Providers (ISPs). When users dial into an ISP they enter a user name and password.
This information is passed to a RADIUS server, which checks that the information is correct, and then
authorizes access to the ISP system.
Router : A device that connects LANs into an internal network and routes traffic between them.
Routing : The process of determining a path to use to send data to its destination.
Routing table : A list of valid paths through which data can be transmitted.
Server : An application that answers requests from other devices (clients). Used as a generic term for any
device that provides services to the rest of the network such as printing, high capacity storage, and network
access.
SMTP, Simple Mail Transfer Protocol : In TCP/IP networks, this is an application for providing mail delivery
services.
SNMP , Simple Network Management Protocol : A set of protocols for managing networks. SNMP works by
sending messages to different parts of a network. SNMP-compliant devices, called agents, store data about
themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters.
SSH , Secure shell : A secure Telnet replacement that you can use to log into another computer over a
network and run commands. SSH provides strong secure authentication and secure communications over
insecure channels.
Subnet : A portion of a network that shares a common address component. On TCP/IP networks, subnets are
defined as all devices whose IP addresses have the same prefix. For example, all devices with IP addresses
that start with 100.100.100. would be part of the same subnet. Dividing a network into subnets is useful for
both security and performance reasons. IP networks are divided using a subnet mask.
Subnet Address : The part of the IP address that identifies the subnetwork.
TCP, Transmission Control Protocol : One of the main protocols in TCP/IP networks. TCP guarantees
delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.
UDP, User Datagram Protocol : A connectionless protocol that, like TCP, runs on top of IP networks. Unlike
TCP, UDP provides very few error recovery services, offering instead a direct way to send and receive
datagrams over an IP network. It is used primarily for broadcasting messages over a network.
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