DNS domain name resolution in a detailed Web request

When we open the browser, enter a URL to request the resources we need, but the URL is to resolve to the corresponding IP address to establish a connection with the remote host, how to resolve the URL to IP is the scope of DNS work, even as a developer, the process we do not feel, but it is true existence, If any DNS server goes bad, it can cause a very serious internet disaster.

The parsing process for the DNS server is as follows:

This DNS resolution is about 10 steps:

The first step: the browser will check if there is no resolved IP address in the cache, if the cache has, this parsing process will end. So a lot of times because of the browser's DNS cache problem, causing access to a resource problem, because the DNS parsing problems.

The second step: if the user's browser is not in the cache, the browser will look for the operating system cache for this domain name corresponding DNS resolution results.

The third step: how, how to know the name server? Our network configuration will have "DNS server address" This option, if the previous two processes can not be resolved, then the domain name will be sent to the Ldns set here, that is, the domain name server in the region. As shown in the following:

In general, this specialized domain name resolver performance will be very good, they will generally cache domain name resolution results, about 80% of the domain name resolution work has been completed here, so Ldns mainly undertook the domain name of the resolution work.

Fourth step: If Ldns is still missing, go directly to the root server domain name server to request resolution.

Fifth step: According to the domain name server returned to the local name server a queried primary domain name server (GLTD server) address. Gltd is an international top-level domain name server, such as. com,. cn,. org, etc., only about 13 units worldwide.

Sixth step: The local DNS server sends a request to the GLTD server, which is returned in one step.

Seventh step: The GLTD server that accepts the request finds and returns the address of the name server that corresponds to the name server, which is usually the name server you are registering with, such as the domain name you are applying for in a domain Name service provider. Then this domain name resolution task is done by the server of the domain name provider.

Eighth step: The name Server name server will query the stored domain name and IP mapping relationship table, under normal circumstances to obtain the destination IP records, along with a TTL value returned to the DNS server domain name server.

Nineth Step: Return the IP and TTL value corresponding to the domain name, Local DNS server caches the domain name and IP correspondence, and the cached time is controlled by the TTL value.

Tenth step: The result of the resolution is returned to the user, the user is cached in the local system cache based on the TTL value, and the domain name parsing process ends.

Clear the cached domain name:

Commands in the general Windows environment are as follows:

DNS domain name resolution in a detailed Web request