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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. A BlueGene supercomputer cabinet. ...
Computer networks redirects here. ...
Time to live of IP datagrams In IPv4, time to live (TTL) is an 8-bit field in the Internet Protocol (IP) header. It is the 9th octet of 20. The time to live value can be thought of as an upper bound on the time that an IP datagram can exist in an internet system. The TTL field is set by the sender of the datagram, and reduced by every host on the route to its destination. If the TTL field reaches zero before the datagram arrives at its destination, then the datagram is discarded and an ICMP error datagram (11 - Time Exceeded) is sent back to the sender. The purpose of the TTL field is to avoid a situation in which an undeliverable datagram keeps circulating on an internet system, and such a system eventually becoming swamped by such immortal datagrams. Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. ...
The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ...
In computer technology and networking, an octet is a group of 8 bits. ...
The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. ...
The Time Exceeded Message is an ICMP message which is generated by a gateway to inform the source of a datagram that the datagram has been discarded due to the time to live field reaching zero. ...
In theory, time to live is measured in seconds, although every host that passes the datagram must reduce the TTL by at least one unit. In practice, the TTL field is reduced by one on every hop. To reflect this practice, the field is named hop limit in IPv6. Internet Protocol version 6 (IPv6) is a network layer protocol for packet-switched internetworks. ...
The Unix traceroute command (tracert on Windows) depends on the functionality of the TTL field. tracert in action on Windows XP. traceroute, or tracepath on modern Linux systems, tracert on Windows operating system, is a TCP/IP utility which allows the user to determine the route packets take to reach a particular host. ...
Time to live of DNS records TTLs also 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). On the Internet, the Domain Name System (DNS) stores and associates many types of information with domain names; most importantly, it serves as the phone book for the internet, translating human-friendly domain names and computer hostnames, e. ...
A name server is a computer server that implements a name service protocol. ...
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. An MX record or Mail exchange record is a type of resource record in the Domain Name System (DNS) specifying how Internet e-mail should be routed. ...
See also For other uses, see Ping (disambiguation). ...
tracert in action on Windows XP. traceroute, or tracepath on modern Linux systems, tracert on Windows operating system, is a TCP/IP utility which allows the user to determine the route packets take to reach a particular host. ...
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