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[br][br]The Domain Name System (DNS) translates Internet domain and host names to IP addresses and vice versa.[br][br]On the Internet, DNS automatically converts between the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites. Larger corporations also use DNS to manage their own company intranet. Home networks use DNS when accessing the Internet but do not use it for managing the names of home computers.[br][br][br]How DNS Works[br]DNS is a client/server network communication systems: DNS clients send requests to and receive responses from DNS servers. Requests containing a name, that result in an IP address being returned from the server, are called forward DNS lookups. Requests containing an IP address and resulting in a name, called reverse DNS lookups, are also supported. DNS implements a distributed database to store this name and last-known address information for all public hosts on the Internet.[br][br]The DNS database resides on a hierarchy of special database servers. When clients like Web browsers issue requests involving Internet host names, a piece of software (usually built into the network operating system) called the DNS resolver first contacts a DNS server to determine the server's IP address. If the DNS server does not contain the needed mapping, it will, in turn, forward the request to a different DNS server at the next higher level in the hierarchy. After potentially several forwarding and delegation messages are sent within the DNS hierarchy, the IP address for the given host eventually arrives at the resolver, that in turn completes the request over Internet Protocol.[br][br]DNS additionally includes support for caching requests and for redundancy. Most network operating systems support configuration of primary, secondary, and tertiary DNS servers, each of which can service initial requests from clients.[br][br][br]Setting Up DNS on Personal Devices and Home Networks[br][br]Internet Service Providers (ISPs) maintain their own DNS servers and use DHCP to automatically configure their customer's networks, Automatic DNS server assignment relieves households of the burden of DNS configuration. Home network administrators are not required to keep their ISPs settings, however. Some prefer to use one of the available public Internet DNS services instead. Public DNS services are designed to offer better performance and reliability over what a typical ISP can reasonably offer.[br][br]Home broadband routers and other network gateway devices store primary, secondary and tertiary DNS server IP addresses for the network and assign them to client devices as needed. Administrators can choose to enter addresses manually or obtain them from DHCP. Addresses can also be updated on a client device via its operating system configuration menus.[br][br]Issues with DNS can be intermittent and difficult to troubleshoot given its geographically-distributed nature. Clients can still connect to their local network when DNS is broken, but they will be unable to reach remote devices by their name. When the network settings of a client device show DNS server addresses of 0.0.0.0, it indicates a failure with DNS or with its configuration on the local network. |
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发表于 2019-05-01 11:48:46
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