When we use the Ping command, we usually pay attention to the value of time = MS, but ignore the value of TTL. When TTL is different from Ping, the value of TTL is different. What is the reason? What is the use of TTL?
What is TTL?
TTL is the abbreviation of Time To Live in English, meaning "survival time value". In short, it means the time of DNS record cache on DNS server.
Suppose that there is such a domain name myhost.Symbolics.com (in fact, this is a DNS record, usually indicates that there is a host named myhost in the Symbolics.com domain) corresponding to the IP address is 184.108.40.206, and its TTL is 10 minutes. This domain name or record is stored on a DNS server named dns.Symbolics.com.
Now there is a user typing the address in the browser (also called URL): myhost.Symbolics.com, what happens?
The DNS server specified by the visitor (or his ISP, Internet service provider, dynamically assigned to him) 220.127.116.11 will try to explain myhost.Symbolics.com for him. Of course, 18.104.22.168 DNS server can not resolve immediately because it does not contain myhost.Symbolics.com information, but after recursive query of global DNS, it finally locates dns.Symbolics.com to the DNS server. The dns.Symbolics.com server will tell the server by the corresponding address of the corresponding server, and then let the user tell the user. 22.214.171.124 in order to speed up the analysis of the myhost.Symbolics.com record, the 126.96.36.199 result is retained for a period of time. This is TTL time. During this period, if the user has an analytical request for myhost.Symbolics.com, it will tell the user 188.8.131.52 directly, and when the TTL expires, it will repeat the above process.
TTL the smaller the better?
The smaller the value of "TTL", the better. Obviously, it is wrong. On the contrary, it should be said that the greater the value of "TTL" is, the better it is, because the greater the value of "TTL", the less the number of packets sent through the router. The less router, the faster the destination will be.
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