Technologies
|
DNS RR
Each domain, whether it is a single host or a top-level domain, can have a set of resource records associated with it. For a single host, the most common record is just its IP address, but many other kinds of resource records also exist. When a resolver gives a domain name to DNS, what it gets back are resource records associated with that name. So the real function of DNS is to map domain names onto the resource records.
The different types of Resource Records and their brief description is as follows: Number / Code / Description Function
- A Network Address: Stores the host name and IP address of individual hosts in the domain. This is the record used to translate host names to IP addresses.
- NS Authoritative Name Server: Stores information used to identify the name servers in the domain that store information for that domain.
- MD Mail Destination; now replaced by MX
- MF Mail forwarder; now replaced by MX
- CNAME Canonical Name: Stores additional host names, or aliases, for hosts in the domain.
- SOA Start Of Authority: Required for every domain. Stores information about DNS itself for the domain
- MB Mailbox domain name
- MG Mailbox member
- MR Mail Rename Domain
- NULL Null Resource Record
- WKS Well-known service: Stores information about the various network services available from hosts in the domain.
- PTR Pointer to a domain name: Stores the IP address and host name of individual hosts in the domain. Used to translate IP addresses into host names.
- HINFO Host Information: Stores information about the hardware for specific hosts.
- MINFO Mailbox Information
- MX Mail Exchange - Stores information about where mail for the domain should be delivered.
- TXT Text string: Stores up to 256 characters of text per line.
- RP Responsible person: Stores information about the person responsible for the domain.
- AFSDB AFS-type services
- X.25 X.25 Address
- ISDN ISDN Address
- RT Route through.
TTL
Time to live (sometimes abbreviated TTL) is a limit on the period of time or number of iterations or transmissions in computer and computer network technology that a unit of data (e.g. a record) can experience before it should be discarded.TTLs occur in the Domain Name System (DNS), where they are set by an authoritative nameserver for a particular Resource Record. When a Caching (recursive) nameserver queries the authoritative nameserver for a Resource Record, it will cache that record for the time (in seconds) specified by the TTL. If a stub resolver queries the caching nameserver for the same record before the TTL has expired, the caching server will simply reply with the already cached resource record rather than retrieve it from the authoritative nameserver again. Nameservers also have TTLs for negative replies (NXDOMAIN); they are generally short in duration (3 hours at most).
Shorter TTLs can cause heavier loads on an authoritative nameserver, but can be useful when changing the address of critical services like web servers or MX records, and therefore are often lowered by the DNS administrator prior to a service being moved, in order to minimize disruptions.
Round robin
Round robin is a load balancing technique in which balance power is placed in the DNS server instead of a strictly dedicated machine as other load techniques do.
Round robin works on a rotating basis in that one server IP address is handed out, then moves to the back of the list; the next server IP address is handed out, and then it moves to the end of the list; and so on, depending on the number of servers being used. This works in a looping fashion.
Round robin DNS is usually used for balancing the load of geographically distributed Web servers. For example, a company has one domain name and three identical home pages residing on three servers with three different IP addresses. When one user accesses the home page it will be sent to the first IP address. The second user who accesses the home page will be sent to the next IP address, and the third user will be sent to the third IP address. In each case, once the IP address is given out, it goes to the end of the list. The fourth user, therefore, will be sent to the first IP address, and so forth.
Whitelisting & Blacklisting
Blacklists, of course are lists of known or suspected spammers that include their IP addresses and perhaps their domain name. Whitelists, on the other hand, are lists of trusted, opt-in e-mailers.
POP3
Local e-mail clients use the Post Office Protocol version 3 (POP3), an application-layer Internet standard protocol, to retrieve e-mail from a remote server over a TCP/IP connection. Nearly all subscribers to individual Internet service provider e-mail accounts access their e-mail with client software that uses POP3.
The design of POP3 and its procedures supports end-users with intermittent connections (such as dial-up connections), allowing these users to retrieve e-mail when connected and then to view and manipulate the retrieved messages without needing to stay connected. Although most clients have an option to leave mail on server, e-mail clients using POP3 generally connect, retrieve all messages, store them on the user's PC as new messages, delete them from the server, and then disconnect. In contrast, the newer, more capable Internet Message Access Protocol (IMAP) supports both connected and disconnected modes of operation. E-mail clients using IMAP generally leave messages on the server until the user explicitly deletes them. This and other facets of IMAP operation allow multiple clients to access the same mailbox. Most e-mail clients support either POP3 or IMAP to retrieve messages; however, fewer Internet Service Providers (ISPs) support IMAP. The fundamental difference between POP3 and IMAP4 is that POP3 offers access to a mail drop; the mail exists on the server until it is collected by the client. Even if the client leaves some or all messages on the server, the client's message store is considered authoritative. In contrast, IMAP4 offers access to the mail store; the client may store local copies of the messages, but these are considered to be a temporary cache; the server's store is authoritative.
IMAP4
The Internet Message Access Protocol (commonly known as IMAP or IMAP4, and previously called Internet Mail Access Protocol, Interactive Mail Access Protocol, and Interim Mail Access Protocol) is an application layer Internet protocol that allows a local client to access e-mail on a remote server. IMAP4 and POP3 (Post Office Protocol version 3) are the two most prevalent Internet standard protocols for e-mail retrieval. Virtually all modern e-mail clients and servers support both.
E-mail messages are generally sent to an e-mail server that stores received messages in the recipient's e-mail mailbox. The user later retrieves these messages with either a web browser or an e-mail client that uses one of a number of e-mail retrieval protocols. While some clients and servers preferentially use vendor specific, typically proprietary protocols, most support the Internet standard protocols SMTP for sending e-mail and POP3 and IMAP4 for retrieving e-mail, allowing interoperability with other servers and clients. For example, Microsoft's Outlook client typically uses a proprietary protocol to communicate with an Exchange server as does IBM's Notes client when communicating with a Domino server, but all of these products also support SMTP, POP3, and IMAP4. Support for the Internet standard protocols allows many other e-mail clients such as Qualcomm's Eudora or Mozilla Thunderbird to access these servers and similarly allows the clients to be used with other servers.
IMAP is often used in large networks; for example, a college campus mail system. IMAP allows users to access new messages instantly on their computers, since the mail is stored on the network. With POP3, users either download the e-mail to their computer or access it via the web. Both methods take longer than IMAP, and the user must either download any new mail or "refresh" the page to see the new messages.
SMTP
Simple Mail Transfer Protocol (SMTP) is the de facto standard for e-mail transmissions across the Internet.
SMTP is a relatively simple, text-based protocol, where one or more recipients of a message are specified (and in most cases verified to exist) and then the message text is transferred.
SMTP is a "push" protocol that does not allow one to "pull" messages from a remote server on demand. To do this a mail client must use POP3 or IMAP. Another SMTP server can trigger a delivery in SMTP using ETRN.
MySQL databases
MySQL (pronounced /mɑɪ ɛs kjuː ɛl/) is a multithreaded, multi-user SQL database management system (DBMS) which has, according to MySQL AB, more than 10 million installations.
MySQL is owned and sponsored by a single for-profit firm, the Swedish company MySQL AB, which holds the copyright to most of the codebase. This is similar to the JBoss model and how the Free Software Foundation handles copyright in its projects, and dissimilar to how the Apache project does it, where the software is developed by a public community and the copyright to the codebase is owned by its individual authors.
FTP
FTP or File Transfer Protocol is used to transfer data from one computer to another over the Internet, or through a network.
Specifically, FTP is a commonly used protocol for exchanging files over any network that supports the TCP/IP protocol (such as the Internet or an intranet). There are two computers involved in an FTP transfer: a server and a client. The FTP server, running FTP server software, listens on the network for connection requests from other computers. The client computer, running FTP client software, initiates a connection to the server. Once connected, the client can do a number of file manipulation operations such as uploading files to the server, download files from the server, rename or delete files on the server and so on. Any software company or individual programmer is able to create FTP server or client software because the protocol is an open standard. Virtually every computer platform supports the FTP protocol. This allows any computer connected to a TCP/IP based network to manipulate files on another computer on that network regardless of which operating systems are involved (if the computers permit FTP access). There are many existing FTP client and server programs. FTP servers can be setup anywhere between game servers, voice servers, internet hosts, and other physical servers.
PHP
PHP (PHP:Hypertext Preprocessor) is a reflective programming language originally designed for producing dynamic web pages. PHP is used mainly in server-side scripting, but can be used from a command line interface or in standalone graphical applications. Textual User Interfaces can also be created using ncurses.
CGI
Abbreviation of Common Gateway Interface, a specification for transferring information between a World Wide Web server and a CGI program. A CGI program is any program designed to accept and return data that conforms to the CGI specification. The program could be written in any programming language, including C, Perl, Java, or Visual Basic.
CGI programs are the most common way for Web servers to interact dynamically with users. Many HTML pages that contain forms, for example, use a CGI program to process the form's data once it's submitted. Another increasingly common way to provide dynamic feedback for Web users is to include scripts or programs that run on the user's machine rather than the Web server. These programs can be Java applets, Java scripts, or ActiveX controls. These technologies are known collectively as client-side solutions, while the use of CGI is a server-side solution because the processing occurs on the Web server.
SSI
Server Side Includes is an easy server-side scripting language used almost exclusively for the web. As its name implies, its primary use is including the contents of a file into another, via a Web Server.
Abbreviated SSI. A type of HTML comment that directs the Web server to dynamically generate data for the Web page whenever it is requested. The basic format for SSIs are:
UNIQ5458b53d51a59b3b-pre-00000001-QINUWhere #command can be any of various commands supported by the Web server. The simplest command is #include, which inserts the contents of another file. This is especially useful for ensuring that boilerplate components, such as headers and footers, are the same on all pages throughout a Web site. To change a boilerplate element, you need only modify the include file, instead of updating every individual Web page.
SSIs can also be used to execute programs and insert the results. They therefore represent a powerful tool for Web developers.
There is no official standard for SSIs, so every Web server is free to support different SSIs in different manners. However, many SSI commands, such as #include and #exec, have become de facto standards.
Web pages that contain SSIs often end with a .shtml extension, though this is not a requirement. The filename extension enables the Web server to differentiate those pages that need to be processed before they are sent to the browser.
PHP MyAdmin
phpMyAdmin is a tool written in PHP intended to handle the administration of MySQL over the Internet. Currently it can create and drop databases, create/drop/alter tables, delete/edit/add fields, execute any SQL statement, and manage keys on fields.
CMS
A Content Management System (CMS) is a software system used for content management. This includes computer files, image media, audio files, electronic documents and web content. The idea behind a CMS is to make these files available inter-office, as well as over the web. A Content Management System would most often be used as archival as well. Many companies use a CMS to store files in a non-proprietary form. Companies using a CMS file share with ease, as most systems use server based software, even further broadening file availability. As shown below, many Content Management Systems include a feature for Web Content, and some have a feature for a "workflow process."
"Workflow" is the idea of moving an electronic document along for either approval, or for adding content. Some Content Management Systems will easily facilitate this process with email notification, and automated routing. This is ideally a collaborative creation of documents. A CMS facilitates the organization, control, and publication of a large body of documents and other content, such as images and multimedia resources.
A web content management system is a content management system with additional features to ease the tasks required to publish web content to web sites.
Web content management systems are often used for storing, controlling, versioning, and publishing industry-specific documentation such as news articles, operators' manuals, technical manuals, sales guides, and marketing brochures. A content management system may support the following features:
- Import and creation of documents and multimedia material
- Identification of all key users and their content management roles
- The ability to assign roles and responsibilities to different content categories or types.
- Definition of the content workflow tasks, often coupled with event messaging so that content managers are alerted to changes in content.
- The ability to track and manage multiple versions of a single instance of content.
- The ability to publish the content to a repository to support access to the content. Increasingly, the repository is an inherent part of the system, and incorporates enterprise search and retrieval.
- Some content management systems allow the textual aspect of content to be separated to some extent from formatting. For example the CMS may automatically set default color, fonts, or layout.
Whois
WHOIS is a TCP-based query/response protocol which is widely used for querying a database in order to determine the owner of a domain name, an IP address, or an autonomous system number on the Internet. WHOIS lookups were traditionally made using a command line interface, but a number of simplified web-based tools now exist for looking up domain ownership details from different databases. Web-based WHOIS clients still rely on the WHOIS protocol to connect to a WHOIS server and do lookups, and command-line WHOIS clients are still quite widely used by system administrators.