What is TTL value?

The full name of the TTL value is "Live Time", which simply means that the DNS record is cached on the DNS server.

To understand the TTL value, consider one of the following examples: Suppose there is such a domain name myhost.abc.com, the corresponding IP address is 1.1 1.1, the TTL is set to 3,600 seconds, this domain name or this record is stored in a DNS server named dns.abc.com.

Now a user type the following address (also known as a URL) in the browser: http://myhost.abc.com what happens then?

The visitor specifies that the DNS server (or his ISP, Internet service provider, dynamically assigned to him) 8.8.8.8 will attempt to parse myhost.abc.com for him, of course 8.8.8.8 This DNS server does not contain Myhost.abc.com this information so that it cannot be resolved immediately, but after a recursive query through global DNS, it eventually navigates to the dns.abc.com DNS server, dns.abc.com This DNS server will myhost.abc.com the corresponding IP address 1.1.1.1 tell 8.8.8.8 the DNS server, and then 8.8.8.8 tell the user the result. 8.8.8.8 in order to speed up the analysis of myhost.abc.com this record, will just 1.1.1.1 the result of a period of time, this time is TTL value, in this period of time if the user has to myhost.abc.com this record resolution request, it directly told the user IP address is 1.1 .1.1, the above procedure is repeated when the TTL expires.