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Domain name space

The domain name space is an inverted tree, with the root directory at the top, and below are some top-level domain names (first-level domain names). Each node in the tree has a text label (text label) that can be up to 63 characters long (excluding "."). An empty label (length 0) is reserved for the root. The reading method is to read from the node up to the root directory.

An absolute domain name is also used to refer to a fully qualified domain name (fully qualified domain name), usually abbreviated to FQDN.

In the case of the same parent node, there can be no child nodes with the same label.

Second, domain

A domain is a subtree in the domain name space. The name of the domain is the domain name of the top node of this subtree.

The darker part of the picture is purdue.edu. The domain of.

Any domain name in the subtree (that is, the domain) is considered part of the domain. A domain name can appear in multiple subtrees, so a domain name can also appear in multiple domains.

It is also easy to understand that larger domains contain smaller domains, and smaller domains are contained by larger domains. Smaller domains contain more specific child nodes. Of course, large domains also include these small nodes.

III. Mainframe

Domain names are just indexes in the DNS database, and "hosts" are domain names that point to the information of each host. Like www.baidu.com. The host name is www.baidu.com, which is actually a device that provides WEB services under the second-level domain name baidu.com. Of course, it has more than one, but it shows a device when it serves.

IV. Resource records

Just as we register book information, we put the corresponding book information under the corresponding directory, and this registration material is called book resource record. Accordingly, the data related to the domain name is stored in the resource record (resource record), referred to as RR. Resource records are divided into different classes (class) according to the type of network or software.

Domain name space on Internet

The original top-level domain name divides the Internet domain name space into seven domains by organization:

Com business organization.

Edu educational institution

Gov government agencies

Mil military department

Net is usually an organization that provides network infrastructure and is later opened up to commercial organizations

Org is usually a non-profit organization

Int International Organization

These domains are called generic top-level domains (generic top-level domain), or gTLD for short. Responsible for managing Internet

ICANN (Internet Corporation for Assigned Names and Numbers) of domain name space system

VI. Authorization

A domain management organization can divide a domain into several subdomains. These subdomains can be authorized to other organizations. This means that these authorized organizations are responsible for maintaining data in their subdomains. It is free to change the data and even subdivide the subdomain into more subdomains before authorizing it. The parent domain retains only pointers to child domain data sources, so that it can point the querier there.

For example, Stanford University manages this subdomain of stanford.edu. However, not all domain management organizations will hand over authorization to the appropriate owner.

Let's take Stanford University as an example.

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