Appendix 16. Glossary Internet Security Router User’s Manual144element of URLs, which identify a specific file at a web site, e.g., http://www.asus.com.See also DNS.download To transfer data in the downstream direction, i.e., from the Internet to the user.DSL Digital Subscriber LineA technology that allows both digital data and analog voice signals to travel overexisting copper telephone lines.Ethernet The most commonly installed computer network technology, usually using twisted pairwiring. Ethernet data rates are 10 Mbps and 100 Mbps. See also 10BASE-T,100BASE-T, twisted pair.filtering To screen out selected types of data, based on filtering rules. Filtering can be applied inone direction (upstream or downstream), or in both directions.filtering rule A rule that specifies what kinds of data the a routing device will accept and/or reject.Filtering rules are defined to operate on an interface (or multiple interfaces) and in aparticular direction (upstream, downstream, or both).firewall Any method of protecting a computer or LAN connected to the Internet from intrusion orattack from the outside. Some firewall protection can be provided by packet filteringand Network Address Translation services.FTP File Transfer ProtocolA program used to transfer files between computers connected to the Internet.Common uses include uploading new or updated files to a web server, anddownloading files from a web server.hop When you send data through the Internet, it is sent first from your computer to a router,and then from one router to another until it finally reaches a router that is directlyconnected to the recipient. Each individual “leg” of the data’s journey is called a hop.hop count The number of hops that data has taken on its route to its destination. Alternatively, themaximum number of hops that a packet is allowed to take before being discarded (seealso TTL).host A device (usually a computer) connected to a network.HTTP Hyper-Text Transfer ProtocolHTTP is the main protocol used to transfer data from web sites so that it can bedisplayed by web browsers. See also web browser, web site.ICMP Internet Control Message ProtocolAn Internet protocol used to report errors and other network-related information. Theping command makes use of ICMP.IGMP Internet Group Management ProtocolAn Internet protocol that enables a computer to share information about its membership inmulticast groups with adjacent routers. A multicast group of computers is one whosemembers have designated as interested in receiving specific content from the others.Multicasting to an IGMP group can be used to simultaneously update the address booksof a group of mobile computer users or to send company newsletters to a distribution list.Internet The global collection of interconnected networks used for both private and businesscommunications.intranet A private, company-internal network that looks like part of the Internet (users accessinformation using web browsers), but is accessible only by employees.IP See TCP/IP.IP address Internet Protocol addressThe address of a host (computer) on the Internet, consisting of four numbers, each