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## 10. Glossary of Terms

This is a list of the meanings of some of the words and acronyms used in this document.

CGI Script

  A Common Gateway Interface Script. This is a program which is run on demand to generate the content of a web page. If a web page has to do more than simply feed an unchanging text and graphics display to the viewer, you will probably need some sort of dynamic content generation program such as a CGI Script. Examples include discussion boards, feedback forms, e-commerce shopping carts, and more.

DHCP

  Dynamic Host Configuration Protocol. A standard, defined in RFC 1531, for computers on a TCP/IP network to request from a central server information such as the IP number they should be using, the netmask, the gateway, etc. Rather than an administrator entering this information into the machine configuration, the machine simply requests it from the server as it is preparing to attach to the network.

DNS

  Domain Name Service. A standard for translating domain names into IP Numbers, or vice versa, by looking up data in centralized databases.

DSL

  Digital Subscriber Line. A relatively high speed network connection, usually delivered through specialized telephone wiring.

Dynamic IP Number

  An IP Number which is assigned periodically or on a per-session basis. No guarantee is made that the number will remain constant. A dynamic IP number might change only when your network connection hangs up and reconnects, or it might change periodically under DHCP negotiation. Certain session-based services such as telnet and ssh will stop working if the IP number of either end of the connection is changed during the session.

Forward DNS Query

  A DNS query which converts a domain name into an IP Number.

FTP

  The File Transfer Protocol. A standard system for sending files between machines over the Internet.

ftpd

  The daemon responsible for providing FTP services on a host. It responds to queries initiated by a remote client.

Internet Service Provider

  See ISP.

IP

  See IP Number.

IP Number

  The ``address'' of a certain network interface. Under the current addressing standard, called ipv4, this number consists of four 8-bit values, generally written as base-10 numbers separated by dots. Communication between computers on the Internet is based on packets of information sent between IP numbers.

ISP

  Internet Service Provider. The company which provides your network connectivity, including connection hardware, service hosting, and leasing out the IP numbers under their control.

Masquerading

  A form of filtering in which packets from one machine to the outside world have their headers rewritten so that they appear to come from an intermediate machine. That intermediate machine then passes responses back to the originating machine. The net effect is that an entire network of machines can appear to use a single IP number, that of the masquerading host, for the purpose of outgoing connections.

named

  The name server daemon. This is the daemon which answers DNS queries, and is distributed as part of the BIND package.

Network Time Protocol

  See NTP.

NTP

  Network Time Protocol. A standard for synchronizing your system clock with the ``true time'', defined as the average of many high-accuracy clocks around the world.

OS

  Operating system. Linux, Windows, FreeBSD, BeOS, HP-UX, etc.

PHB

  Pointy-Haired Boss. A creation of Scott Adams, of Dilbert fame.

Provider

  See ISP.

Reverse DNS Query

  A DNS query which converts a IP Number into a domain name.

Router

  A specialized hardware device which implements rules for where to send packets based on their IP Numbers, and which bridges between your Ethernet hardware and whatever communications medium connects you to your ISP.

ssh

  The secure shell. A cryptographically strong replacement for rlogin, telnet, ftp, and other programs. Protects against ``spoofing'', man in the middle attacks, and packet sniffing.

Static IP Number

  An IP Number which has been assigned or leased to you permanently. Barring revocation of the agreement which granted you this number, that IP number will always be available for your use, and no other machine on the Internet is allowed to use that number. Contrast this with Dynamic IP Numbers.

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