台北科技大学：《计算机网络》（英文版） NP04 18

Domain name System DNS) Chuan-Ming Li CSIE NTUT Spring 04, TAIWAN

1 Domain Name System (DNS) Chuan-Ming Liu CSIE, NTUT Spring ’04, TAIWAN

Contents O NAME SPACE O DOMAIN NAME SPACE O DISTRIBUTION OF NAME SPACE O DNS IN THE INTERNET O RESOLUTION O DNS MESSAGES O TYPES OF RECORDS O COMPRESSION O EXAMPLES

2 Contents  NAME SPACE  DOMAIN NAME SPACE  DISTRIBUTION OF NAME SPACE  DNS IN THE INTERNET  RESOLUTION  DNS MESSAGES  TYPES OF RECORDS  COMPRESSION  EXAMPLES

Domain Name System (DNS) o System mapping a name to an address o Using host file when the size of the Internet Is smal o as the Internet grows the host file becomes too large to store o Two solutions for huge amount information in a host file o Store entire host file into a single computer e divide the information into smaller parts and store each part on a different computer

3 Domain Name System (DNS)  System mapping a name to an address  Using host file when the size of the Internet is small  As the Internet grows, the host file becomes too large to store  Two solutions for huge amount information in a host file ⚫ Store entire host file into a single computer ⚫ Divide the information into smaller parts and store each part on a different computer

Domain Name System o Providing the service for querying the corresponding ip address or the domain name o a distributed database system o Database is divided into several sub-database and each sub-database is self-maintained e Using client-server architecture o Using tree data structure o By replication and caching to achieve consistency, efficiency, and stability o The largest database system in the world

4 Domain Name System  Providing the service for querying the corresponding IP address or the domain name  A distributed database system ⚫ Database is divided into several sub-database and each sub-database is self-maintained ⚫ Using client-server architecture ⚫ Using tree data structure ⚫ By replication and caching to achieve consistency, efficiency, and stability. ⚫ The largest database system in the world

Name Space o Each host on the internet has an unique Ip address for TCP/IP protocol o An unique name is assigned to each host instead of numbers for people to remember o Name space mapping each address to a unique name ●Flat o Hierarchical (this is what we used today

5 Name Space  Each host on the Internet has an unique IP address for TCP/IP protocol  An unique name is assigned to each host instead of numbers for people to remember  Name space mapping each address to a unique name ⚫ Flat ⚫ Hierarchical (this is what we used today)

Domain Name Space o Hierarchical name space o Using an inverted -tree structure where o root is at the top o the tree has 128 levels(0 to 127) o each level defines a hierarchical level each node has a label having maximum of 63 characters

6 Domain Name Space  Hierarchical name space  Using an inverted-tree structure where ⚫ root is at the top ⚫ the tree has 128 levels (0 to 127) ⚫ each level defines a hierarchical level ⚫ each node has a label having maximum of 63 characters

Figure: Domain Name Space arpa como edu g d 8o bb

7 Figure: Domain Name Space

Label o Root label is a null string(empty string o Children of a node have different labels

8 Label  Root label is a null string (empty string)  Children of a node have different labels

Domain name o Each node in the tree represents a domain name o a full domain name is a sequence of labels separated by dots(.) o The domain names are read from the node up to the root o The last label is the label of the root (null)

9 Domain Name  Each node in the tree represents a domain name  A full domain name is a sequence of labels separated by dots (.).  The domain names are read from the node up to the root.  The last label is the label of the root (null)

Root Domain names Label and labels du edu. Domain name Label fhdafhda.edu. Domain name Label atcO atc thda.edu. Domain name Label challenger challenger. atc. fda.edu. I Domain name

10 Domain names and labels