Ch19_DNS - Domain Name System (DNS) Your current safe...

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Chapter 19 1 Domain Name System (DNS) Your current safe boundaries were once unknown frontiers. - Unknown
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Chapter 19 2 Objectives Describe the need for DNS and how DNS is organized Explain what is meant by domains and zones Describe how DNS handle name resolution requests, and the difference between recursive and iterative resolutions requests Explain the types of roles that DNS servers can play on a network, including the root servers, primary and secondary servers List commonly used resource records in a zone file
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Chapter 19 3 DNS History and Background Early methods for resolving symbolic names, such as microsoft.com, to numeric IP addresses relied completely on static text files, called HOSTS.TXT . With the rapid growth of number of hosts, this mechanism did not scale well. DNS was designed as a distributed database of information (such as: domain names and addresses) about hosts Distributed nature allows local control of the segments of the overall database, yet data in each segment is available across the entire network through a client-server scheme. Robustness and adequate performance are achieved through replication and caching .
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Chapter 19 4 DNS Structure The Domain Name System (DNS) is basically a database of host information. The service DNS provides is information about internet hosts. The structure of the DNS in hierarchical in design. Names are defined in an inverted tree , with the root node at the top The entire DNS tree represents the domain name space . Each intersection point where the tree branches is called a node . The maximum depth of the tree is 128 levels (0-127). Each node in the tree has a text label up to 63 characters long. A null (zero-length) label is reserved for the root. The full domain name of any node is the sequence of labels from that node toward the root (“up” the tree), with dots separating the names in the path.
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Chapter 19 5 DNS Structure Beneath the root, there are top-level or first-level domains . Some top-level domains are organizational , such as: .com .edu .gov .mil .net .org .int There are also top-level domains with country codes (such as: .ca for Canada, .fr for France, etc.) Top-level domain called arpa (called the inverse domain ) is used for mapping IP addresses to host domain names
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Chapter 19 6 Figure 19.2 Domain name space
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Chapter 19 7 Figure 19.3 Domain names and labels
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Chapter 19 8 What is a Domain? A Domain is a subtree of the domain name space. The name of a domain is the same as the domain name of the node at the top of the subtree.
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Chapter 19 9 Name Servers and Zones The information contained in the domain name space is distributed among many computers called Domain Name Servers . What a server is “responsible for” or “has authority over” is
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Ch19_DNS - Domain Name System (DNS) Your current safe...

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