Lead: If yesterday afternoon (January 21) that you want to go online to brush microblogging look at the video, it is a bit cumbersome. Almost all of China's large sites falters. In fact, this is not your home network because there is anything wrong. Look at the news will know, is the Internet's root name server problems, resulting in domain names have been pointing to the wrong IP address, thereby affecting access to these domains. This is how it specifically? Why root domain name server problems have such a great impact on the server is the story behind this?
If yesterday afternoon (January 21) that you want to go online to brush microblogging look at the video, it is a bit cumbersome. Almost all of China's large sites or falters on the on the on the "Page Fault" the. In fact, this is not your home network because there is anything wrong. Look at the news will know, is the Internet's root name server problems, resulting in domain names have been pointing to the wrong IP address, thereby affecting access to these domains. And so on, why the problem of root name servers have such a great impact on the server is the story behind this?
To clarify this issue, we must first know how Domain Name Service (DNS) works. In the beginning, the domain name of this simple and quick way to access does not exist on the Internet. A site wants to access thousands of miles away, or a server, all using IP address, which is similar to a string of numbers such as 65.49.2.178. IP address is like a phone number in life, can be precisely targeted to a particular machine or service. However, with the use, people will think it is too inconvenient. Like the phone number is difficult to remember, like, want to rely on a large number of head to remember the IP site is ridiculous. Therefore, DNS will assume the "telephone directory assistance" work, is responsible for helping us remember domain name will simply be converted to the correct IP address, eliminating the need for memory "telephone number" of trouble. As long as we know the IP address of the DNS server's IP address can be found in all the other sites. So we enter the domain name in the browser when visiting the fact, or IP address, browser just to help us find the correct IP address from the DNS, and we usually do not know the process.
But all go to the same DNS server queries above, there will be problems. Imagine thousands of people while a phone call to directory assistance inquiries, what will happen? Few people get through the phone, and the majority has been busy, finding the desired phone number. Meanwhile, the telephone number of the world where there is a telephone directory assistance, check the telephone process will be very slow. In order to solve these two problems, DNS to do so two things: First, set up a number of DNS servers so that they constitute a tree structure. At the time of the query from the root name servers start, layer by layer investigation continues. Secondly, the allocation for each region a local domain name server, the server is responsible for this query to the root name servers, because the local domain name server can cache, which can greatly reduce the burden on the root servers.
Therefore, we only need to know the IP address of the local domain name server, and give the local domain name server "call" query. At the time of normal access to a domain, if the local domain name server just is not cached, the procedure is as follows:
Wang to the local domain name server "phone": Hello, I am asking about http://www.baidu.com corresponding to "phone number."
Local domain name server Operator: Please wait.
Operator queries the record at hand, we found no http://www.baidu.com IP address, so to root name servers "Call."
Local domain name server operators: root name server Hello, I want to check http://www.baidu.com corresponding to "phone number."
Root name server operator to view the record at hand: I do not have specific "telephone number", but I know that you can find on the .com domain name server. I can give you a .com domain name server "phone numbers."
Local domain name server operator to get the .com domain name server "phone numbers" to continue to call it.
Local domain name server operators: .com domain name server Hello, I want to check http://www.baidu.com corresponding to "phone number."
Operator .com domain name server on the record at hand is still not find a specific "phone number", then told a local domain name server operators, this phone can be found on baidu.com domain name server.
Local domain name server operator third phone call: baidu.com domain name server Hello, I want to check http://www.baidu.com corresponding to "phone number."
baidu.com domain name server operators have found that the hands of the domain name corresponding to the record, it will http://www.baidu.com correct "phone number" and told the local domain name server operator.
Finally, the local name server operator to correct this "phone number" charged to your book, then told Wang, considered completed the inquiry.
Li next time another user to the local domain name server "called" Query http://www.baidu.com "phone numbers", the local name server operator will find that already have their hands on the last little book Wang left record query. This time he does not need to be scaled up to the root name servers "Call", and only need to record your own book on the "phone number" told Alan, you can complete the query. Of course, if the query interval of Mary and Tom for a long time, in order to prevent http://www.baidu.com "telephone number" is changed on this record book will be treated as invalid records, operator or will re-query the whereabouts of root name servers.
In the understanding of how DNS works after the root name servers Why is there such a big impact is obvious. Even with the presence of the local domain name server, in the final analysis, correspondence between domain names and IP addresses or from the root name servers provided by the local domain name server cache only play a role. Therefore, once the root name server errors, all the user wants to resolve domain names, you will eventually get a wrong IP address. Since the directory assistance tells us is that a wrong call, we naturally get through.
Yesterday the accident is still unknown reasons. There could be an internal DNS server failure, there may be caused by a hacker attack. But for whatever reason, DNS server for the entire Internet has obvious importance, how to protect the root name servers from attack, security experts will also become a topic in need of special attention in the future.
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