Time to Live

The Time to live (TTL, German lifetime) is the term of validity, the data is given in computer networks.

Internet Protocol

In the Internet Protocol ( IP) specifies the TTL, how many intermediate stations (hops ) must pass a data packet on the Internet. The data field for the TTL field is one octet (8 -bit field ), so the maximum number of hops is 255. With each hop, the TTL is decremented by 1. When a data packet after its TTL has not yet reached its destination, it is discarded. The last station sends the ICMP reply type 11: Time exceeded with code 0: Time to live exceeded in transit to the sender. Deliberately applied this method for example, the program traceroute.

The TTL of the Internet Protocol has been rarely implemented according to the Internet standard that it was in IPv6 replaced by a simple equal -sized hop limit and the lifetime is up to the higher layer protocols.

Domain Name System

In the Domain Name System (DNS) is the TTL of each resource records how long a name resolution just was expected to remain at least valid. During this period can be made to the DNS caching. After the TTL, the client should discard the particular name resolution and repeat if necessary.

During a short TTL can lead to significant load of servers, delayed a long TTL necessary changes accordingly. A not unusual TTL of 86,400 seconds for example, means that any change is complete only after 24 hours. In contrast, use dynamic DNS services TTL values ​​of typically 60 seconds for timely each new data will be used according to ( frequent ) changes of address.

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