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(also Time to Live)

DNS TTL definition

DNS TTL is a setting that specifies how long a query should be stored in the DNS resolver's cache before it must be resubmitted. The TTL recursive or local resolver will save the information it has acquired in its cache before making another round of requests for fresh information. The favorable effect of the rapid resolution of DNS lookups on the speed of web browsing is obvious. By having a local resolver cache, a person can compare that to the local copy much more quickly than they could by looking up the DNS record.

TTL values

  • SOA TTL. The time between when the SOA (start of authority) record is refreshed.
  • Refresh TTL. The interval during which secondary servers are configured to refresh the primary zone file from the primary server.
  • Retry TLL. Repeated attempts by a secondary server to refresh the primary zone file after an unsuccessful initial attempt.
  • Expiry TLL. After refresh and retry fail constantly, the primary should be deemed gone and no longer authoritative.
  • NX TLL. This is the maximum amount of time the recursor will wait before returning an NXDOMAIN response after the domain name query fails.