1. Domain Name System

2. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 So what is DNS Resolution? DNS Resolution is the procedure used to resolve a IP address from a domain name. This is very similar to how we get the phone number of a person we want to contact. It is all based on hierarchy.

3. 25.1 Name Space Flat Name Space Hierarchical Name Space

4. 25.2 Domain Name Space Label Domain Name

5. Figure 25.1 Domain name space

6. Figure 25.2 Domain names and labels

7. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Managed by UofT DNS Name hierarchy DNS hierarchy can be represented by a tree Root and top-level domains are administered by an Internet central name registration authority (ICANN) Below top-level domain, administration of name space is delegated to organizations Each organization can delegate further Managed by ECE Dept.

8. 25.6 DNS Messages Header Question Section Answer Section Authoritative Section Additional Information Section

9. Figure 25.3 FQDN ( Fully Qualified Domain Name) and PQDN

10. Figure 25.4 Domains

11. 25.3 Distribution of Name Spaces Hierarchy of Name Servers Zone Root Server Primary and Secondary Servers

12. Figure 25.5 Hierarchy of name servers

13. A primary server loads all information from the disk file; the secondary server loads all information from the primary server. Note:

14. 25.4 DNS In The Internet Generic Domain Country Domain Inverse Domain

15. Figure 25.7 DNS in the Internet

16. Figure 25.8 Generic domains

17. Table 25.1 Generic domain labels LabelDescription comCommercial organizations eduEducational institutions govGovernment institutions intInternational organizations milMilitary groups netNetwork support centers orgNonprofit organizations

18. Table 25.2 New generic domain labels LabelDescription aeroAirlines and aerospace companies bizBusinesses or firms (similar to com) coopCooperative business organizations infoInformation service providers museumMuseums and other nonprofit organizations namePersonal names (individuals) proProfessional individual organizations

19. Figure 25.9 Country domains

20. Figure 25.10 Inverse domain

21. 25.5 Resolution Resolver Mapping Addresses to Names Recursive Resolution Iterative Resolution Caching Mapping Names to Addresses

22. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004

23. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004

24. Figure 25.11 Recursive resolution

25. Figure 25.12 Iterative resolution

26. DNS can use the services of UDP or TCP, using the well-known port 53. Note: