Chapter 2 application layer 2.4 DNS

Summary of computer network top-down method 2.4DNS Directory services on the Internet

Catalog

2.4 DNS： Directory services on the Internet

2.4.1 DNS Services provided

2.4.2 DNS Working mechanism overview

2.4.3 DNS Records and messages

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2.4 DNS： Directory services on the Internet

         One way to identify a host is to use its Host name （hostname）. It can also be used. IP Address （IP address） Are identified .

        2.4.1 DNS Services provided

        The domain name system （Domain Name System,DNS） It is mainly used for host name to IP Directory services for address translation .DNS See the book for the detailed introduction of the definition .

        DNS Also provide ： get Host alias （host aliasing） Corresponding Host specification name （cannonical hostname）, Email server alias （mail server aliasing） Corresponding host specification name , Load distribution （load distribution）.

        2.4.2 DNS Working mechanism overview

        DNS Request and reply messages use UDP Datagram via port 53 send out .

        The problems of centralized design include ： A single point of failure , Communication capacity , Remote centralized database , maintain .

        Distributed 、 Hierarchical database ： There are three types of DNS The server ： root DNS The server , Top-level domain （Top-Level Domain,TLD）DNS The server and Authoritative server . There are also classes of important DNS Server is Local DNS The server （local DNS server）（ Also called the default name server ）.

        Query methods include recursive query （recursive query） and Iterative query （iterative query）.

        DNS A feature of the system ：DNS cache （DNS caching）, You can make DNS Queries bypass some DNS The server . See the book for details .

        2.4.3 DNS Records and messages

        DNS The server stores Resource records （Resource Record,RR）RR Provided host name to IP Address mapping . A resource record is a record that contains （Name,Value,Type,TTL） Of 4 Tuples . See the book for details .

        DNS The message only includes query message and answer message , And have the same format .

        stay DNS When inserting records into a database, you need to insert records into DNS Insert multiple resource records into the server , See the book for details .