After studying this chapter 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. | Chapter 18 Domain Name System (DNS) CONTENTS NAME SPACE DOMAIN NAME SPACE DISTRIBUTION OF NAME SPACE DNS IN THE INTERNET RESOLUTION DNS MESSAGES TYPES OF RECORDS COMPRESSION EXAMPLES DDNS ENCAPSULATION NAME SPACE DOMAIN NAME SPACE Figure 18-1 Domain name space Figure 18-2 Domain names and labels Figure 18-3 FQDN and PQDN Figure 18-4 Domains DISTRIBUTION OF NAME SPACE Figure 18-5 Hierarchy of name servers Figure 18-6 Zones and domains A 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 INTERNET Figure 18-7 DNS in the Internet Figure 18-8 Generic domains Figure 18-9 Country domains Figure 18-10 Inverse domain RESOLUTION Figure 18-11 Recursive resolution Figure 18-12 Iterative resolution DNS MESSAGES Figure 18-13 DNS messages Figure 18-14 Query and response messages Figure 18-15 Header format Figure 18-16 QR: Query/Response OpCode: 0 standard, 1 inverse, 2 server status AA: Authoritative TC: Truncated RD: Recursion Desired RA: Recursion Available rCode: Status of the error Flags fields TYPES OF RECORDS Figure 18-17 Question record format Figure 18-18 . Query name format Figure 18-19 Resource record format COMPRESSION Figure 18-20 Format of an offset pointer EXAMPLES Example 1 A resolver sends a query message to a local server to find the IP address for the host “.”. We discuss the query and response messages separately. Figure 18-21 Example of a query message Figure 18-22 Example of a response message Example 2 An FTP server has received a packet from an FTP client with IP address . The FTP server wants to verify that the FTP client is an authorized client. Figure 18-23 Example of inverse query message Figure 18-24 Example of inverse response message DDNS ENCAPSULATION DNS can use the services of UDP or TCP using the well-known port 53. | Chapter 18 Domain Name System (DNS) CONTENTS NAME SPACE DOMAIN NAME SPACE DISTRIBUTION OF NAME SPACE DNS IN THE INTERNET RESOLUTION DNS MESSAGES TYPES OF RECORDS COMPRESSION EXAMPLES DDNS ENCAPSULATION NAME SPACE DOMAIN NAME SPACE Figure 18-1 Domain name space Figure 18-2 Domain names and labels Figure 18-3 FQDN and PQDN Figure 18-4 Domains DISTRIBUTION OF NAME SPACE Figure 18-5 Hierarchy of name servers Figure 18-6 Zones and domains A 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 INTERNET Figure 18-7 DNS in the Internet Figure 18-8 Generic domains Figure 18-9 Country domains Figure 18-10 Inverse domain RESOLUTION Figure 18-11 Recursive resolution Figure 18-12 Iterative resolution DNS MESSAGES Figure 18-13 DNS messages Figure 18-14 Query and response messages Figure 18-15
