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Internet Glossary

Copyright © 1999, 2000, 2003, 2005, 2007-2015, 2018, 2020-2021 by David E. Ross

In my other Web pages, I use terms such as server and domain, which I need to define. Here are simplified definitions that might not be as complete or technically precise as an experienced computer professional might desire.

To simplify browsing, this page might appear in a window or tab separate from the pages where the terms are used. You can leave this page open and return to the page that sent you here without having to reload either. However, after this page has opened on one definition, the user who then selects another term will have to select this page to bring it in front.

The worldwide network of Internet systems that connect one ISP to another. Different companies or government agencies — the backbone providers — operate different portions of the network.
Sometime called a "favorite", this is an entry in a browser's database that facilitates requesting a Web page that the user visits frequently. Instead of having to enter the URI in a browser's input area to reach the page, the user merely selects the bookmark from a list of bookmarks.
See crawler
A group of computers under the control of hostile software that causes them to act in concert. The software effectively makes the computers act as robots (the bot in botnet) under the control of someone who is not authorized to have such control. The result is a network (the net in botnet) of computers. Botnets are often used to send spam that cannot be traced back to the actual originator, but botnets are also responsible for activities that are far more sinister and hostile.

Usually, a botnet results from infections by computer viruses or similar malware. The best way to avoid being infected by a botnet is to use effective anti-virus software that is updated regularly.

Software that provides a user with the interfaces — input, menus, displays — to use a server. E-mail and Web-browsing software on a PC are clients.
A data center containing servers that can be used for storing data and supporting communications accessible by authorized users in dispersed locations, including while traveling. Such a data center might include access to software or act as a backup to a local in-house data center. Often, the term is used to refer to a commercial service. See Cloud computing at Wikipedia for details.
An automated application (also known as a bot, a shortened form of robot) that seeks and visits Web pages, not to view them but to collect information from them. Some crawlers analyze text content to index Web pages for search engines (e.g., Google, Yahoo). Some crawlers seek E-mail addresses embedded in Web pages in order to build mailing lists for spammers. The Internet Archive uses a crawler to collect complete Web pages for its archive.
The symbolic name of a server or other entity accessible through the Internet. Examples of domains are,, and
Domain name server, a server that translates domain names into IP addresses and vice versa. A DNS looks in a database table — the DNS table (of course) — to perform this task. There are many DNSs scattered across the Internet. While they do not all have identical tables, DNSs are constantly updating their tables as domains move from one host to another.

When a client requests a domain by name, the client's Internet connection accesses the nearest DNS to search its DNS table. If the domain name does not appear in that table, the DNS in turn accesses a farther DNS. This continues until either the name is found or the chain of DNSs is exhausted. Obviously, most DNSs contain in their tables. Less well-known domains are carried in only a few tables. All domains are carried in the tables at the root DNSs at the ends of the chains.

See bookmark.
A line at the beginning of an Internet message that describes the message, its origin, or its routing through the Internet. Among headers are the Subject, From, and To that appear when viewing an E-mail message. However, all Internet messages contain headers that direct the routing of the messages to their destinations. A message requesting a Web page generally consists only of headers, one of which might be a cookie previously set on your computer by a prior visit to that page; the returned file for that page has headers to direct the file back to your browser and might include a new or updated cookie. Thus, both servers and clients create and use headers.

Headers are generated when a message is sent. Then more headers are added as the message travels through the Internet. A mail server will generally add even more headers when an E-mail message is received. Often, headers in spam messages are faked to prevent tracing their origins.

Technically, a header as described above is a header field. A group of header fields is the header section of a message. Samples of E-mail, newsgroup, and Web headers are presented in a text page to preserve their actual layout.

The computer on which a client or server operates (is hosted). This is sometimes called the server's platform.
Internet Message Access Protocol, an interface for your E-mail client to access incoming E-mail messages held at a mail server. This protocol defines the way your E-mail client communicates with the server to display messages without downloading them (except temporarily). Thus, with IMAP, E-mail messages generally remain on their mail server until you take explicit action to delete them. This makes it possible for you to access your accumulated messages from several different computers. IMAP is often used to access E-mail via a Web browser. (See also POP.)
IP address
The numeric address of a domain on a host. The address is used to route requests and data over the Internet.

The classic IP address (IPv4) is in the form of four groups of 3-digit decimal numbers in the range 0-255 separated by periods; leading zeros in each group are omitted. The IPv4 scheme can result in 4,294,967,296 unique addresses. Many domains have multiple IP addresses to allow multiple connections at the same time. The IPv4 addresses for range from to

Six-part IP addresses (IPv6) are gradually being introduced because of concerns that not enough distinct four-part IPv4 addresses can exist. With every smart cell-phone, WiFi hot spot, GPS device, router, and Internet-of-things (IoT) device having its own IP address and with many servers having multiple IP addresses, that concern is very real.

An IPv6 address is in the form of eight groups of 4-digit hexadecimal digits in the range 0-FFFF (0-65535) separated by colons. Leading zeros in each group are omitted. One set of consecutive groups that are all zeros may be replaced by a double colon (::). The number of unique IPv6 addresses is greater than 34 followed by 37 zeros. The IPv6 address for is represented as 2a01:4f8:120:9382::145, which is actually 2a01:04f8:0120:9382:0000:0000:0000:0145.

When I used a dial-up modem for connecting to the Internet, I got a new IP address each time I connected. This is a dynamic IP address. Before I retired, I had a dedicated ethernet connection at work, which gave me a static, unchanging IP address. Often, DSL and cable modem connections are static; but some ISPs assign a new IP address each time a computer with such a connection reboots or when the modem reboots. If I am absent from my house for several days, I unplug my modem; when I return and plug in my modem, I sometimes get a new IP address.

If a domain moves from one host to another, a new IP address is assigned to the domain because IP addresses are associated with a particular host's connection to the Internet. Thus, the old IP address becomes available for reassignment to another domain on the old host.

In addition to domains, other connections to the Internet have IP addresses, including your own computer, which has the IP address

Note: If you connect to the Internet through a local router and then through a modem, that might be the IP address of either of those devices.

Internet Service Provider, the company through which you connect to the Internet.
"Modem" is actually an abbreviation of "modulator-demodulator". In the Internet, this is the device that connects something (e.g., a computer) to the Internet.
open relay
An E-mail server configured to accept and send messages from individuals who have not logged in (i.e., from users who are not on the server's user list). Since open relays appear to be the original sources of relayed messages (not merely an intermediary), they are often used by spammers to hide the real source. The configuration that permits an E-mail server to be an open relay generally indicates an error by an ISP's (or other server operator) system administrators. To block spam, many ISPs configure their mail servers to reject messages appearing to originate from open relays.
See host.
A router connects various devices — computers, printers, modems, etc — together to form a network. See Our Local Area Network (LAN) for my own network as an example.
  1. Point of presence (also termed PoP), the place where your phone line, T1 line, TV cable, et cetera connects to the Internet or where different ISPs connect to the backbone. When using a dial-up modem, the phone number you dial is at the POP.

    There are also dial-up pseudo-POPs, which are very similar to call-forwarding (and might even use that capability). If you dial a pseudo-POP, you actually connect to a different phone number. Thus, when I worked in Los Angeles County, I could call my ISP on a local phone number. I would then connect to a POP in Ventura County more than 40 miles away. If I were to dial the actual POP, it would not be a local call.

  2. Post Office Protocol (also termed POP3), an interface for your E-mail client to access and retrieve incoming E-mail messages held at a mail server. This protocol defines the way your E-mail client communicates with the server to download the messages and store them on your local computer, optionally deleting them from the server. Some ISPs do not use POP3, requiring subscribers to use only the ISP's own proprietary E-mail clients. (See also IMAP and SMTP.)
Software that performs a task as requested by a client. In general, a server performs tasks such as searching a database or retrieving E-mail — tasks that require major computer power — while a client performs data-processing activities such as collecting inputs to send to a server and generating displays from data retrieved by a server. Users are very aware of clients but not necessarily aware of their supporting servers.

Servers generally operate in one of two modes:

Because many hosts only host one server, the term server is often used for the hardware; this can only cause confusion when the same platform is a host to multiple copies of a server or several different servers and might even host some clients. (Good system design, however, generally avoids having clients and servers hosted on the same platform.) Also, a given server might be launched on several different hosts when requested; this improves the responsiveness of the server.

site certificate
A file used to establish a secure, authenticated connection between a user's computer and a Web site. A site certificate is used by a bank or other business to assure its customers that their Web site is indeed authentic. It also provides the means to encrypt and decrypt data going back and forth between the user's computer and the Web server.

A site certificate is digitally signed by a certificate authority (CA). A CA has a root certificate that is used to encrypt part of a site certificate, thereby signing the latter. Actually, there is usually an intermediate certificate that was signed by a root certificate; the intermediate certificate then signed the site certificate.

For all this to work, the site certificate is installed on the Web server along with any intermediate certificates; and the root certificate is installed in a database contained within the user's Web browser. (A frequent problem arises when those who maintain the Web server fail to install the necessary intermediate certificates.) Most browsers come with a large repertoire of root certificates. Also, for this to work, the Web pages are addressed beginning with https instead of http, the s indicating secure. The URI beginning with https must have the domain that agrees with the domain in the site certificate.

Simple Mail Transfer Protocol, the interface used by an E-mail client to send outgoing E-mail messages. Actually, SMTP applies to both outgoing and incoming messages. However, many clients use POP (second definition) or IMAP for incoming messages. In some cases, there are separate servers for SMTP and either POP or IMAP.
See the discussion of this term:
Use a fake UA string to make a Web server act as if a browser being used is different from the actual browser (e.g., as if Opera were being used when actually Firefox is being used). Spoofing may be necessary when trying to access a Web site that is incorrectly sniffing UA strings.
User agent. The client used on the Internet, usually a browser or E-mail application. The brand and version of a user agent is usually indicated by the UA string, an identifier sent by the user agent to a server when requesting a response (e.g., a Web page, an E-mail message).

At the time this page was last updated, my browser was SeaMonkey 2.49.5, which had the UA string

Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:52.0) Gecko/20100101 SeaMonkey/2.49.5

This means:

(Note that the default UA string for this version of SeaMonkey is
  Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.5
where the insertion of Firefox/52.0 is a built-in spoof of Firefox. I have disabled that spoof.)

Your UA string is

CCBot/2.0 (

NOTE: Accessing a Web page from a server while using a UA that leaves a blank or null UA string is contrary to RFC 1945 and might be considered abusive.

Uniform resource identifier, uniform resource locator

The symbolic address of a Web page or other Internet entity. The URI for this page is

While the term URI (uniform resource identifier) has replaced URL, URL remains in common usage. Although the definition of URI is more generalized than URL, the difference is mostly in technical details.

There is a convention that URIs in text should be bracketed, with a preference for using < and >. If a URI will appear split between two or more lines, this can be especially useful in determining the full extent of the URI. Thus, this page is at <>; and my home page is at <>. However, when entering a URI in a form on a Web page or within an HTML-formatted E-mail message, [ and ] might be a better choice for brackets since < and > have special meanings in HTML.

WhoIs is an Internet service that provides the ownership data for a domain or IP address. This ownership data often includes contact information. For a domain, a WhoIs query generally provides the name of the owner and the identity of the domain registry. For an IP address, a WhoIs query will generally give the range of addresses bracketing the specific address that are all under the same ownership. There are a number of Web-based WhoIs services and also freeware WhoIs applications that can be installed on a computer.

The WhoIs data for the domain is

Registry Domain ID: D51687756-LROR
Registrar WHOIS Server:
Registrar URL:
Updated Date: 2015-12-12T10:16:19Z
Creation Date: 2001-01-13T00:12:14Z
Registry Expiry Date: 2023-01-13T00:12:14Z
Registrar Registration Expiration Date:
Registrar: MarkMonitor Inc.
Registrar IANA ID: 292
Registrar Abuse Contact Email:
Registrar Abuse Contact Phone: +1.2083895740
Domain Status: clientDeleteProhibited
Domain Status: clientTransferProhibited
Domain Status: clientUpdateProhibited
Registrant Organization: Wikimedia Foundation, Inc.
Registrant State/Province: CA
Registrant Country: US
DNSSEC: unsigned

The WhoIs data for the IPv4 address is

NetRange: -
NetName:        AMAZON-2011L
NetHandle:      NET-54-224-0-0-1
Parent:         NET54 (NET-54-0-0-0-0)
NetType:        Direct Allocation
OriginAS:       AS16509
Organization:   Amazon Technologies Inc. (AT-88-Z)
RegDate:        2012-03-01
Updated:        2012-04-02

OrgName:        Amazon Technologies Inc.
OrgId:          AT-88-Z
Address:        410 Terry Ave N.
City:           Seattle
StateProv:      WA
PostalCode:     98109
Country:        US
RegDate:        2011-12-08
Updated:        2017-01-28
Comment:        All abuse reports MUST include:
Comment:        * src IP
Comment:        * dest IP (your IP)
Comment:        * dest port
Comment:        * Accurate date/timestamp and timezone of activity
Comment:        * Intensity/frequency (short log extracts)
Comment:        * Your contact details (phone and email) Without these we will be unable to identify the correct owner of the IP address at that point in time.

OrgTechHandle: ANO24-ARIN
OrgTechName:   Amazon EC2 Network Operations
OrgTechPhone:  +1-206-266-4064 

OrgAbuseHandle: AEA8-ARIN
OrgAbuseName:   Amazon EC2 Abuse
OrgAbusePhone:  +1-206-266-4064 

OrgNOCName:   Amazon AWS Network Operations
OrgNOCPhone:  +1-206-266-4064 

No, do not ask me to explain each line in these WhoIs results.

Note: Because of privacy legislation in the European Union, the amount of information in a WhoIs entry for a European domain or IP address may be severely limited. To some extent, this impairs the usefulness of WhoIs for identifying the source of spam and malware.

Last updated 29 December 2021

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