Title: Domain Naming Service and HOSTS
Course: 2016FA-MCO-110-401 > Section: Module 9: Networking

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Domain Naming Service (DNS)

The Domain Naming service is a hierarchal tool by which domain names are translated into IP addresses. Most commonly utilized for Internet Communications, this service makes it easier for users to remember a specific resource rather than recalling a specific IP address. DNS utilizes a distributed database system to store the translation tables. This means that when a domain name is specified, the request will be routed from server to server until the appropriate Name to IP entry is found and returned.

DNS Record Types

DNS Records are the de facto mapping record which allow a DNS Server to determine with which IP a domain name is associated. In addition to these DNS Records, there are commands that dictate the action of the DNS Server. These DNS Records, or syntax types, provide additional instruction sets that allow the server to determine the information returned. Some of the more commonly utilized record types are listed below. A or AAAA – Address Record: “A” returns a 32bit IPv4 address, while “AAAA” returns a 128bit IPv6 address. CNAME – Canonical Name Record: Gives a destination the ability to be known by one or more hostnames.

There must be an associated “A” record for this to function to operate successfully. EX: Neo.Morpheus.com CNAME Bill.Rufus.com will direct all request going to Neo.Morpheus.com to Bill.Rufus.com MX – Mail Exchange Record: identifies the mail exchange servers available for a specific domain SSHFP – SSH Public Key Fingerprint: This is a record of the public host fingerprints used in SSH authentication. These records assist in verifying authenticity of the host. These are just a few of the available DNS record types. The list is updated as additional functionalities are added to the DNS Record. The Records and accompanying functionalities are managed by the Internet Engineering Task Force (IETF) through various RFC’s (Request for Comments).

The DNS Hierarchy

As stated previously, the DNS System is hierarchal. This means that each portion of the DNS address represents a different level of the hierarchy. As stated before, domains are hierarchal. A few examples of Top Level Internet Domain Names are as follows:

- .COM – Commercial Organization
- .EDU – Educational Institution
- .GOV – Government Institution
- .MIL – Military Group
- .NET – Network Organization (originally used by Service Providers, it is now utilized by all manner of businesses)
- .ORG – Organization Group
- .INT – International Organization

From a hierarchal standpoint, the computers represented in the host name example of the company Rufus.com would be represented on the Internet as Bill.Rufus.com and Ted.Rufus.com respectively. This would be translated as .COM (1st level indicating commercial entity), .Rufus (2nd level or subdomain indicating Rufus Company), .Bill or .Ted (3rd level or subdomain indicating .Bill or .Ted division of .Rufus Company).

DNS Name Resolution

What happens when a web address is entered in your web browser? The website, or DNS Name must be resolved to an IP address to allow connection and transmission of data from the requested site. This is called the DNS Name Resolution Process. It is, as is the nature of DNS, a hierarchal process. If illustrated, it would follow a path similar to the outline below.

1. Website address request is made and routed to a top level DNS server (.com,.gov,.net)
2. DNS Server receives the request and checks its HOSTS file in attempt to resolve the request.
3. If unresolvable, request is sent to another server for resolution Server may resolve request to domain (Rufus.com).
4. If there is a specific host required, the request is forwarded to a DNS server within the Rufus Domain for translation.
5. DNS Server within Rufus Domain resolves request to Bill Host.
6. IP address of resolved Bill.Rufus.Com is returned to requesting device and connection is established.

HOSTS File

The HOSTS file is plain text file utilized by devices to resolve a host name to an IP address. HOSTS files contain a listing of IP addresses and their related host names. The HOSTS file is based in the client computers/Server’s operating system and is purely updated by the local administrator. It is the first point of validation of a requested host name before a DNS server is addressed.

Objectives met:
- C9
- 9.9
- 9.10
- 9.11