TTL - MDN Web Docs Glossary: Definitions of Web-related terms 编辑

TTL can refer either to :

the lifetime of a packet in a network can do before being released
the expiry time of cached data

Networking

In networking, the TTL, embedded in the packet, is a usually defined as a number of hops or as an expiration timestamp after which the packet is dropped. It provides a way to avoids network congestion, but releasing packets after they roamed the network too long.

Caching

In the context of caching, TTL (as an unsigned 32-bit integer) being a part of the HTTP response header or the DNS query, indicates the amount of time in seconds during which the ressource can be cached by the requester.