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Understanding DNS: Organization, Domains, and Resolution

This chapter explores the organization of the Domain Name System (DNS), including the hierarchical domain name space, distribution of name space, DNS in the internet, name-address resolution, DNS messages, types of records, and Dynamic DNS (DDNS).

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Understanding DNS: Organization, Domains, and Resolution

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  1. Chapter 17 Domain NameSystem: DNS Objectives Upon completion you will be able to: • Understand how the DNS is organized • Know the domains in the DNS • Know how a name or address is resolved • Be familiar with the query and response formats • Understand the need for DDNS TCP/IP Protocol Suite

  2. 17.1 NAME SPACE The names assigned to machines must be unique because the addresses are unique. A name space that maps each address to a unique name can be organized in two ways: flat or hierarchical. The topics discussed in this section include: Flat Name Space Hierarchical Name Space TCP/IP Protocol Suite

  3. 17.2 DOMAIN NAME SPACE The domain name space is hierarchical in design. The names are defined in an inverted-tree structure with the root at the top. The tree can have 128 levels: level 0 (root) to level 127. The topics discussed in this section include: Label Domain Name Domain TCP/IP Protocol Suite

  4. Figure 17.1Domain name space TCP/IP Protocol Suite

  5. Figure 17.2Domain names and labels TCP/IP Protocol Suite

  6. Figure 17.3FQDN and PQDN TCP/IP Protocol Suite

  7. Figure 17.4Domains TCP/IP Protocol Suite

  8. 17.3 DISTRIBUTION OF NAME SPACE The information contained in the domain name space is distributed among many computers called DNS servers. The topics discussed in this section include: Hierarchy of Name Servers Zone Root Server Primary and Secondary Servers TCP/IP Protocol Suite

  9. Figure 17.5Hierarchy of name servers TCP/IP Protocol Suite

  10. Figure 17.6Zones and domains TCP/IP Protocol Suite

  11. Note: A primary server loads all information from the disk file; the secondary server loads all information from the primary server. When the secondary downloads information from the primary, it is called zone transfer. TCP/IP Protocol Suite

  12. 17.4 DNS IN THE INTERNET The domain name space (tree) is divided into three different sections: generic domains, country domains, and the inverse domain. The topics discussed in this section include: Generic Domains Country Domains Inverse Domain Registrar TCP/IP Protocol Suite

  13. Figure 17.7DNS used in the Internet TCP/IP Protocol Suite

  14. Figure 17.8Generic domains TCP/IP Protocol Suite

  15. Table 17.1 Generic domain labels TCP/IP Protocol Suite

  16. Table 17.1 Generic domain labels (Continued) TCP/IP Protocol Suite

  17. Figure 17.9Country domains TCP/IP Protocol Suite

  18. Figure 17.10Inverse domain TCP/IP Protocol Suite

  19. 17.5 RESOLUTION Mapping a name to an address or an address to a name is called name-address resolution. The topics discussed in this section include: Resolver Mapping Names to Addresses Mapping Addresses to Names Recursive Resolution Iterative Resolution Caching TCP/IP Protocol Suite

  20. Figure 17.11Recursive resolution TCP/IP Protocol Suite

  21. Figure 17.12Iterative resolution TCP/IP Protocol Suite

  22. 17.6 DNS MESSAGES The DNS query message consists of a header and question records; the DNS response message consists of a header, question records, answer records, authoritative records, and additional records. The topics discussed in this section include: Header TCP/IP Protocol Suite

  23. Figure 17.13DNS messages TCP/IP Protocol Suite

  24. Figure 17.14Query and response messages TCP/IP Protocol Suite

  25. Figure 17.15Header format TCP/IP Protocol Suite

  26. Figure 17.16Flags field TCP/IP Protocol Suite

  27. Table 17.2 Values of rCode TCP/IP Protocol Suite

  28. 17.7 TYPES OF RECORDS Two types of records are used in DNS. The question records are used in the question section of the query and response messages. The resource records are used in the answer, authoritative, and additional information sections of the response message. The topics discussed in this section include: Question Record Resource Record TCP/IP Protocol Suite

  29. Figure 17.17Question record format TCP/IP Protocol Suite

  30. Figure 17.18Query name format TCP/IP Protocol Suite

  31. Table 17.3 Types TCP/IP Protocol Suite

  32. Table 17.4 Classes TCP/IP Protocol Suite

  33. Figure 17.19Resource record format TCP/IP Protocol Suite

  34. 17.9 DDNS The Dynamic Domain Name System (DDNS) updates the DNS master file dynamically. TCP/IP Protocol Suite

  35. 17.10 ENCAPSULATION DNS uses UDP as the transport protocol when the size of the response message is less than 512 bytes. If the size of the response message is more than 512 bytes, a TCP connection is used. TCP/IP Protocol Suite

  36. Note: DNS can use the services of UDP or TCP using the well-known port 53. TCP/IP Protocol Suite

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