Domain Name System

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.

25.1 Name Space Flat Name Space Hierarchical Name Space

25.2 Domain Name Space Label Domain Name

Figure 25.1 Domain name space

Figure 25.2 Domain names and labels

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.

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

Figure 25.3 FQDN ( Fully Qualified Domain Name) and PQDN

Figure 25.4 Domains

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

Figure 25.5 Hierarchy of name servers

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

25.4 DNS In The Internet Generic Domain Country Domain Inverse Domain

Figure 25.7 DNS in the Internet

Figure 25.8 Generic domains

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

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

Figure 25.9 Country domains

Figure Inverse domain

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

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

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

Figure Recursive resolution

Figure Iterative resolution

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