Bài giảng TCP/IP - Chapter 18: Domain Name System (DNS)

Chapter 18Domain NameSystem(DNS)CONTENTS NAME SPACE DOMAIN NAME SPACE DISTRIBUTION OF NAME SPACE DNS IN THE INTERNET RESOLUTION DNS MESSAGES TYPES OF RECORDS COMPRESSION EXAMPLES DDNS ENCAPSULATIONNAME SPACE18.1DOMAINNAMESPACE18.2Figure 18-1Domain name spaceFigure 18-2Domain namesand labelsFigure 18-3FQDN and PQDNFigure 18-4DomainsDISTRIBUTION OFNAME SPACE18.3Figure 18-5Hierarchy of name serversFigure 18-6Zones and domainsA primary server loads all information from the disk file; the secondary server loads all information from the the primary server. When the primary downloads information from the secondary, it is called zone transfer.DNS IN THE INTERNET18.4Figure 18-7DNS in the InternetFigure 18-8Generic domainsFigure 18-9Country domainsFigure 18-10Inverse domainRESOLUTION18.5Figure 18-11Recursive resolutionFigure 18-12Iterative resolutionDNSMESSAGES18.6Figure 18-13DNS messagesFigure 18-14Query and response messagesFigure 18-15Header formatFigure 18-16QR: Query/ResponseOpCode: 0 standard, 1 inverse, 2 server statusAA: AuthoritativeTC: TruncatedRD: Recursion DesiredRA: Recursion AvailablerCode: Status of the errorFlags fieldsTYPESOFRECORDS18.7Figure 18-17Question record formatFigure 18-18admin.atc.fhda.edu.Query name formatFigure 18-19Resource record formatCOMPRESSION18.8Figure 18-20Format of an offset pointerEXAMPLES18.9Example 1A resolver sends a query message to a local server to find the IP address for the host “chal.fhda.edu.”. We discuss the query and response messages separately.Figure 18-21Example of a query messageFigure 18-22Example of a response messageExample 2An FTP server has received a packet from an FTP client with IP address 153.2.7.9. The FTP server wants to verify that the FTP client is an authorized client. Figure 18-23Example of inverse query messageFigure 18-24Example of inverseresponse messageDDNS18.10ENCAPSULATION18.11DNS can use the services of UDP or TCP using the well-known port 53.