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Time To Live
Time to live (TTL) or hop limit is a mechanism which limits the lifespan or lifetime of data in a computer or network. TTL may be implemented as a counter (digital), counter or timestamp attached to or embedded in the data. Once the prescribed event count or timespan has elapsed, data is discarded or revalidated. In computer networking, TTL prevents a data packet from circulating indefinitely. In computing applications, TTL is commonly used to improve the performance and manage the cache (computing), caching of data. Description The original DARPA Internet Protocol's Request for Comment, RFC describes TTL as: IP packets Under the Internet Protocol, TTL is an 8-bit field. In the IPv4 header, TTL is the 9th octet (computing), octet of 20. In the IPv6 header, it is the 8th octet of 40. The maximum TTL value is 255, the maximum value of a single octet. A recommended initial value is 64. The time-to-live value can be thought of as an upper bound on the time that an IP datagram c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Counter (digital)
In digital electronics, a counter is a sequential logic circuit that counts and stores the number of positive or negative transitions of a clock signal. A counter typically consists of flip-flop (electronics), flip-flops, which store a value representing the current count, and in many cases, additional logic to effect particular counting sequences, qualify clocks and perform other functions. Each relevant clock transition causes the value stored in the counter to increment or decrement (increase or decrease by one). A digital counter is a finite state machine, with a ''clock'' input signal and multiple output signals that collectively represent the state. The state indicates the current count, encoded directly as a binary number, binary or binary-coded decimal (BCD) number or using encodings such as one-hot or Gray code. Most counters have a ''reset'' input which is used to initialize the count. Depending on the design, a counter may have additional inputs to control functions suc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IPv6
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion, and was intended to replace IPv4. In December 1998, IPv6 became a Draft Standard for the IETF, which subsequently ratified it as an Internet Standard on 14 July 2017. Devices on the Internet are assigned a unique IP address for identification and location definition. With the rapid growth of the Internet after commercialization in the 1990s, it became evident that far more addresses would be needed to connect devices than the 4,294,967,296 (232) IPv4 address space had available. By 1998, the IETF had formalized the successor protocol, IPv6 which uses 128-bit addresses, theoretically all ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Traceroute
In computing, traceroute and tracert are diagnostic command-line interface commands for displaying possible routes (paths) and transit delays of packets across an Internet Protocol (IP) network. The command reports the round-trip times of the packets received from each successive host (remote node) along the route to a destination. The sum of the mean times in each hop is a measure of the total time spent to establish the connection. The command aborts if all (usually three) sent packets are lost more than twice. Ping, however, only computes the final round-trip times from the destination point. For Internet Protocol Version 6 (IPv6), the tool sometimes has the name traceroute6 and tracert6. Implementations A command is available in many modern operating systems, generally named traceroute in Unix-like systems such as FreeBSD, macOS, and Linux and named tracert in Windows and ReactOS. The functionality was available graphically in macOS, but has been deprecated sinc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ping (networking Utility)
ping is a computer network administration software utility used to test the reachability of a host (network), host on an Internet Protocol (IP) network. It is available in a wide range of operating systems including most embedded network administration software. Ping measures the round-trip time for messages sent from the originating host to a destination computer that are echoed back to the source. The name comes from active sonar terminology that sends a Pulse (signal processing), pulse of sound and listens for the echo to detect objects under water. Ping operates by means of Internet Control Message Protocol (ICMP) Network packet, packets. ''Pinging'' involves sending an ICMP echo request to the target host and waiting for an ICMP echo reply. The program reports errors, packet loss, and a statistical summary of the results, typically including the minimum, maximum, the mean (average), mean round-trip times, and standard deviation of the mean. Command-line options and Comp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hop (telecommunications)
In telecommunications, a hop is a portion of a signal's journey from source to receiver. Examples include: #The excursion of a radio wave from the Earth to the ionosphere and back to the Earth. The number of hops indicates the number of reflections from the ionosphere.Federal Standard 1037C #A similar excursion from an earth station to a communications satellite to another station, counted similarly except that if the return trip is not by satellite, then it is only a half hop. In computer network A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...s, a hop is the step from one network segment to the next. References Telecommunications engineering Radio frequency propagation {{Telecomm-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HTTP Cookie
HTTP cookie (also called web cookie, Internet cookie, browser cookie, or simply cookie) is a small block of data (computing), data created by a web server while a user (computing), user is browsing a website and placed on the user's computer or other device by the user's web browser. Cookies are placed on the device used to access a website, and more than one cookie may be placed on a user's device during a session. Cookies serve useful and sometimes essential functions on the World Wide Web, web. They enable web servers to store program state, stateful information (such as items added in the shopping cart in an Online shopping, online store) on the user's device or to track the user's browsing activity (including clicking particular buttons, access control, logging in, or recording which Web browsing history, pages were visited in the past). They can also be used to save information that the user previously entered into Form (HTML), form fields, such as names, addresses, passw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IT Disaster Recovery
IT disaster recovery (also, simply disaster recovery (DR)) is the process of maintaining or reestablishing vital infrastructure and systems following a natural or human-induced disaster, such as a storm or battle. DR employs policies, tools, and procedures with a focus on IT systems supporting critical business functions. This involves keeping all essential aspects of a business functioning despite significant disruptive events; it can therefore be considered a subset of business continuity (BC). DR assumes that the primary site is not immediately recoverable and restores data and services to a secondary site. IT service continuity IT service continuity (ITSC) is a subset of BCP, which relies on the metrics (frequently used as key risk indicators) of recovery point/time objectives. It encompasses IT disaster recovery planning and the wider IT resilience planning. It also incorporates IT infrastructure and services related to communications, such as telephony and data communi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MX Record
A mail exchanger record (MX record) specifies the mail server responsible for accepting email messages on behalf of a domain name. It is a resource record in the Domain Name System (DNS). It is possible to configure several MX records, typically pointing to an array of mail servers for load balancing and redundancy. Overview Resource records are the basic information element of the Domain Name System (DNS). An MX record is one of these, and a domain may have one or more of these set up, as below: The characteristic payload information of an MX record is a preference value (above labelled "Priority"), and the domain name of a mailserver ("Host" above). The priority field identifies which mailserver should be preferred - in this case the values are both 10, so mail would be expected to flow evenly to both ''onemail.example.com'' and ''twomail.example.com'' - a common configuration. The host name must map directly to one or more address records (A, or AAAA) in the DNS, and mu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Web Servers
A web server is computer software and underlying hardware that accepts requests via HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, commonly a web browser or web crawler, initiates communication by making a request for a web page or other resource using HTTP, and the server responds with the content of that resource or an error message. A web server can also accept and store resources sent from the user agent if configured to do so. The hardware used to run a web server can vary according to the volume of requests that it needs to handle. At the low end of the range are embedded systems, such as a router that runs a small web server as its configuration interface. A high-traffic Internet website might handle requests with hundreds of servers that run on racks of high-speed computers. A resource sent from a web server can be a pre-existing file ( static content) available to the web server, or it can be generated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of DNS Record Types
This list of DNS record types is an overview of resource records (RRs) permissible in zone files of the Domain Name System The Domain Name System (DNS) is a hierarchical and distributed name service that provides a naming system for computers, services, and other resources on the Internet or other Internet Protocol (IP) networks. It associates various information ... (DNS). It also contains pseudo-RRs. Resource records Other types and pseudo-RRs Other types of records simply provide some types of information (for example, an HINFO record gives a description of the type of computer/OS a host uses), or others return data used in experimental features. The "type" field is also used in the protocol for various operations. Obsolete record types Progress has rendered some of the originally defined record-types obsolete. Of the records listed at IANA, some have limited use, for various reasons. Some are marked obsolete in the list, some are for very obscure services, some ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stub Resolver
The Domain Name System Security Extensions (DNSSEC) is a suite of extension specifications by the Internet Engineering Task Force (IETF) for securing data exchanged in the Domain Name System ( DNS) in Internet Protocol ( IP) networks. The protocol provides cryptographic authentication of data, authenticated denial of existence, and data integrity, but not availability or confidentiality. Overview The original design of the Domain Name System did not include any security features. It was conceived only as a scalable distributed system. The Domain Name System Security Extensions (DNSSEC) attempt to add security, while maintaining backward compatibility. of 2004 documents some of the known threats to the DNS, and their solutions in DNSSEC. DNSSEC was designed to protect applications using DNS from accepting forged or manipulated DNS data, such as that created by DNS cache poisoning. All answers from DNSSEC protected zones are digitally signed. By checking the digital signatur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
