Domain Name System - DNS

Question 1

DNS - general characteristics

Answer 1

• provides translation between symbolic names for IP hosts and their IP addresses
• provides logical hierarchical view of the Internet - globally distributed database implemented in hierarchy of many name servers

Question 2

DNS - functioning

Answer 2

• application-layer protocol - communicate to resolve names (address/name translation) - application calls resolver
• client/server interaction:
  1. clients: query servers to resolve names (nslookup function)
  2. servers: run name server daemons, reply to queries (bind, named)
• gethostbyname: UNIX based resolver library call that can be invoked from an application program

Question 3

DNS - centralized

Answer 3

• single point of failure
• traffic volume
• distant centralized database
• maintenance
• does not scale

Question 4

DNS - distributed

Answer 4

• no server has all name-to-IP address mappings
• local name servers - each org/ISP has local name server; host DNS query first goes to local name server
• authoritative name server - store the host’s IP address & name; can perform name/address translation for that host’s name
• root name server - contacts authoritative name server if name mapping not known and returns that mapping to local name server

Question 5

Structure of DNS names

Answer 5

• sequence of alphanumeric components separated by periods
• domain names are case insensitive
• each component name up to 63 characters long, entire path up to 255 characters
• names are hierarchical, with most significant component on the right
• left-most component is the computer name