TTL（生存时间）
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TTL 是[[dns|DNS]]记录中指定[[dns-cache|缓存]]响应有效时长（秒）的值。TTL 越低，DNS 变更的传播越快，但会增加对[[authoritative-dns|权威服务器]]的查询负载。
示例
A TTL of 300 (5 minutes) means DNS changes propagate quickly; a TTL of 86400 (24 hours) reduces server load but delays updates.