Basic knowledge of DNS

1, DNS is the domain name server, his task is to determine the domain name of the resolution, such as a record MX records and so on.

2, any domain name has at least one DNS, is generally 2. Why do you need more than 2? Because DNS can be used for recycling, the first parsing failure can be found in a second. So as long as there is a normal DNS resolution, it will not affect the normal use of the domain name.

3, how to determine the DNS domain name?
Very simple to http://www.internic.net/whois.html input you want to query the domain name can be seen. This is the International Domain name Management Center. The only authority. As long as you can find a domain name, it means that the domain name is in effect. It says when you expire and when it expires.

4. Valid DNS indicates who the DNS server is currently working on, such as the query result is NS.XINNETDNS.COM, NS. Xinnet. CN (new network letter sea) means that the current domain name is by NS.XINNETDNS.COM, NS. Xinnet. CN (new network letter Sea) is responsible for parsing. The settings for other DNS are not valid.

5, DNS can be modified. The change will take 24-72 hours before the whole world can refresh. InterNIC information is generally available after 24 hours. In addition, the modification of the process does not mean that the domain name will stop parsing, as long as you are on the 2 side of the parsing. If this is the case, the new DNS is in effect. If it's not in effect. Is that the old DNS is at work. Either in effect or not in effect. There is no 2 time that does not work. So domain name resolution, will not be interrupted. The premise is that both sides have done parsing.

6, DNS is cached.
1, the visitor's computer; 2, your ISP access provider.
Simple example: For example, if you visit www.tydncn.com, your computer first inquires whether there are any cached www.tydncn.com records on this machine. If there is a direct call no longer to search. That is, if you have just visited www.tydncn.com, this time even telecommunications DNS and NS.XINNETDNS.COM, NS. Xinnet. CN (new network letter sea) can not be resolved. is also able to parse out the domain name normally.
It is simple to clear the native DNS cache method. Turn off IE and then clear the history, or reboot the computer.
Then there is the DNS cache for the ISP's access provider.
ISPs are local Internet access providers. For example, we are here in Fujian Telecom, Fuzhou Netcom, Nanping railcom and so on. Every place is not the same. DNS and NS.XINNETDNS.COM, NS for ISPs. Xinnet. CN (new network letter sea) Such DNS is different. Ns. Xinnetdns.com, NS. Xinnet. CN (new network letter Sea) only responsible for the specific resolution, not responsible for caching. The ISP's DNS is responsible for querying and caching only and is not responsible for parsing.
Briefly describe the situation where you have just visited www.tydncn.com. If the www.tydncn.com record does not exist on this computer. Your computer will query the DNS of your local ISP. The ISP's DNS is cached only. That means he'll check for www.tydncn.com cache. If so, he sends the www.tydncn.com record directly to the user. Users will also be able to access the. If there is no www.tydncn.com record in the ISP's cache, then he further queries tydncn.com DNS. Then go to the corresponding DNS to get the data directly and return to the user. When the first user accesses the www.tydncn.com, the www.tydncn.com record is also cached on the ISP's DNS. He won't have to go to NS again. Xinnetdns.com, NS. Xinnet. CN (new network letter Sea) to look for. He will not look up unless there is a new domain name. For example, when visiting the bbs.tydncn.com, he will have to check again.

7, the ISP's DNS cache has a time limit. It's usually 1 hours. Before and after 2 intervals of 1 hours, he went to the domain name of DNS to regain data. Here is the first and current comparison. That is to say, if the time gap is large, go back to the DNS server for domain names. So the refresh is very necessary, otherwise cached once. After the domain name record has changed. The ISP will never find a new record. Knowing this principle, you will understand why records that were not previously registered and effective will be very quick. The changes will be slow to come into effect. is because of the caching reason. But without caching, access can be inefficient because any input www.tydncn.com must run to the NS.XINNETDNS.COM, NS. Xinnet. CN (new network letter Sea) to query records.

Note: Many domain name business Domain name resolution system is not refreshed in real time. Usually set the next time, such as 10 minutes. That is, after you set up a new a record, the domain name server will be added to you in 10 minutes. The goal is to conserve server resources. Be afraid of the client's DNS constant refresh record. Refreshing a record definitely requires a certain amount of resources to be consumed. And the refresh process is not resolvable. In addition, the refresh process is about 5 seconds. This means that the DNS of the domain name quotient within 5 seconds is not available.