Other Important TCP/IP Standards Domain Name System (DNS) Autoconfiguration Protocols

Domain Name System (DNS) Only IP addresses are official –e.g., –These are 32-bit binary numbers –Only they fit into the 32-bit destination and source address fields of the IP headers IP Packet 32-bit Source and Destination Addresses ( )

Domain Name System (DNS) Users typically only know host names –e.g., voyager.cba.hawaii.edu –More easily remembered, but –Will not fit into the address fields of an IP packet IP Packet voyager.cba.hawaii.edu NO

Domain Name System (DNS) User’s computer sends a DNS host the target host’s host name in a DNS Request message DNS host returns the target host’s IP address in DNS Response message User PC Internet Layer Process DNS Host Voyager.cba. hawaii.edu

Domain Name System (DNS) Subtlety –Organizations or ISPs have local DNS hosts –These hosts must know only local host names and IP addresses –For other host names, local DNS host passes request to another DNS host User PC Internet Layer Process Local DNS Host Remote DNS Host

Domain Name System (DNS) Subtlety –Remote DNS host passes information back to the local DNS host –Local DNS host passes information back to user PC –Browser only talks to local DNS host User PC Internet Layer Process Local DNS Host Remote DNS Host

Domain Names Internet uses hierarchical naming –A domain is a collection of resources managed by an organization Generic top level domains (gTLD) by type of organization –.comfor commercial organizations –.edufor educational institutions National top level domains (nTLDs) by country –.UKUnited Kingdom –.AUAustralia

Domain Names Organizations are given second-level domain names –Microsoft.com –Hawaii.edu –JAIMS.org –panko.com –Whitehouse.gov Also can have second-level domains for products (nameofnewmovie.com)

Domain Names Organizations can create lower-level domain names –cba.hawaii.edu (for the College of Business Administration) The lowest level domain name is the host name for an individual host or router – – –

Autoconfiguration Every computer attached to the Internet is a host –Including desktop PCs Every host must have an IP address Some hosts, such as routers and webservers, get permanent IP addresses –So that they can be found easily

Autoconfiguration User PCs do not need permanent IP addresses –They only need to be found within a use session –They usually are given temporary IP addresses each time they use the Internet –They may get a different IP address each time they use the Internet

Autoconfiguration Request-Response Cycle –User software requests IP address for the user PC in Autoconfiguration Request message –Autoconfiguration Response message contains temporary IP address to use in current session User PC Autoconfiguration Host Autoconfiguration Request Temporary IP Address in Autoconfiguration Response

Autoconfiguration Most popular autoconfiguration protocol is DHCP –Dynamic Host Configuration Protocol –Built into Windows after Win 3.1 –Supplies host with temporary IP address DHCP can give more information too –Usually gives IP address of a default gateway (Microsoft terminology for router) –Can give IP address of a local DNS host –Can give other information