Internet Addressing Essay, Research Paper

Internet Addressing

By Gail Battista

Domain Name System lets you have name to number mappings on your computer. The name decel.ecel.uwa.edu.au is the number 130.95.4.2 and vice versa. This is achieved through the DNS. The DNS is a heirachy. There are a small number of root domain severs that are responsible for tracking the top level domains and who is under them. The root domain servers between them know all about the people who have name servers that are authoritive for domains under the root.

Top Level Domains

The original top-level domains divided the Internet domain name space organizationally. There are seven main top-level domains:

.com-Commercial organizations. ex: Hewlet Packard (hp.com) or IBM (ibm.com)

.edu-Educational organizations. ex: U.C. Berkley (berkley.edu)or Perdue University (perdue.com)

.mil-Military organizations. ex: Army (army.com) or Navy (navy.com)

.Net-Networking organizations ex: NSFNET (nsf.com)

.org- Noncommercial organizations ex: Electronic Frontier Foundation (eff.org)

.int- International organizations ex: NATO (nato.com)

There is also a top-level domain called arpa, which was originally used during the ARPANET’s transition from host tables to DNS. All ARPANET hosts originally had host names under arpa so that they were easily found. Later, they moved onto various subdomains of the organizational top-level domains.

(The Internet began as the ARPANET, a U.S. funded research project)

To accommodate the internationalization of the Internet, the implementors of the Internet name space compromised. Instead of insisting all top-level domains describe organizational affiliation, they allowed for geographical designations too. New top-level domains were reserved (not necessarily created) to correspond to individual countries. Their domain names following an existing international standard called ISO 3166. ISO 3166 establishes official two letter abbreviation for every country in the world, ex: Australia’s top-level domain: au, has subdomains like edu.au . U.S. top-level domains has 50 subdomains ( two letter abbreviations, one for each state)

Name Servers

Programs that store information about the domain space are called name servers. Name servers have complete information about some part of the domain name space, called a zone. The name server is then said to have authority for that zone. Name servers can be authoritive for many zones too. The difference between a zone and a domain: a zone contains the domain names and data that a domain contains,except for domain names and data that are delegated elsewhere. Ex: The top-level domain ca (Canada) may have the subdomains ab.ca, on.ca and qb.ca, for the provinces Alberta and Quebec. Authority for the ab.ca, on.ca, on.ca and qb.ca, domains may be delegated to organization in each of the provinces. The domain ca contains all the data in ca plus all the data in ab.ca, on.ca and qb.ca, but the zone ca contains only the data in ca.

There are two types of Names servers, primary and secondary masters. A primary master name server gets the data for the zones it’s authoritive from files on the host it runs on. A secondary master name server gets it’s zone data from another name server authoritive for that zone. When a secondary starts up, it contacts the name server it updates from and if necessary, pulls the zone data over (zone transfer).

Mapping addresses to names

Address to name mapping is used to make output easier for people to read and interpet. It is also used in some authoritization checks. Ex: UNIX host maps addresses to host names to compare against entries in .rhosts and hosts.eqviv files. Address to name mapping requires a sequential search through the host table for an address. This search will return the official host name listed.

Nodes in the in-addr.arpa domain are named after the numbers in the dotted-octet representation of IP addresses. (Dotted – octet representation refers to the common method of expressing 32-bit IP addresses as four numbers in the range 0 to 255, separated by dots). The in-addr.arpa domain can have up to 256 domains, one corresponding to each possible value int first octet of an IP address. Each of these sub-domains could have up to 256 subdomains of it’s own, corresponding to the possible values of the secound octet. There are resourse records attached to the final octet giving the full domain name of the host or network of that IP address.

When a IP address is read it appears backwards, since the name is read “leaf to root”. Ex: if winnie.corp.hp.com has the IP address 15.16.192.152 the corresponding in.addr.arpa, which maps back to domain name winnie.corp.hp.com.