The DNS service – Part1 –


w   In this article we will continue discovering interesting features about Windows Server. In the last article I’ve talked about NetBIOS, a legacy naming resolution protocol. Now it’s time to talk about the naming resolution standard, the DNS or Domain Name System. This is probably the core service in the Internet and one of the most important components of any network. I will try to cover all the aspects of this role so that in the end, you’d have a whole picture of DNS. Just like NetBIOS, DNS is used to translate names into IP addresses. Because DNS is build in a hierarchical structure, it provides a scalable naming resolution mechanism for large networks.
   In order to understand the functionality of DNS you have to understand the basic concepts behind DNS Namespace and Domain Names. The Namespace refers to the root of this hierarchical design. The DNS root of the Internet and any private network is known as ” “. The root contains all the top-level domains like .gov, .org, .com, .net, etc. A Domain Name is an identity given to a certain entity to distinguish itself among all other domain names in the Internet. Let’s take as example our domain ittrainingday.com: the top level domain is .com and the primary DNS suffix is ittrainingday. All domain names can have multiple sub-domains. As long as ittrainingday.com belong to us, we can create as many sub-domains as we want. For example mail.ittrainingday.com or web.ittrainingday.com. Any host that is reachable from the internet would be identified by its FQDN or fully qualified domain name. Let’s take an example: suppose we have a web server that hosts our website. Remember that our domain DNS suffix is ittrainingday. If this server was named server1, then its FQDN would be server1.ittrainingday.com. We will talk about DNS records in a future article and you will better understand fully qualified domain names. Any FQDN would contain the trailing dot (.) at the end. This is actually the starting point of a DNS query and it represents the root of the Internet. You will never see the actual dot when surfacing the Internet because most browsers will not display it by default. There are two types of Domain Namespace:
Public – top-level domains that are routed through the Internet and are uniquely assigned to an entity. These are the common .com or .gov domains and are also known as organizational domains. The public domains also include geographical domains which corresponds to a particular country. For example: .ro, .uk or .us.
Private – domain names which are visible inside private networks only. Usually, large enterprises have their own private namespace with their own DNS infrastructure (you can view it as a private but smaller version of the Internet). These domains are not visible outside the network this is why any name can be assigned to a private domain
Besides these two Domain Names type, there are the reverse domains which are configured in both private and public domains. The reverse domains contain the records for reverse lookups and are named in-addr.arpa. We will talk about DNS queries in a future article.
There are several DNS components that you will have to familiarize with. I will try to cover all of them and describe their role and functionality in the DNS process:
DNS Server – a server that hosts a DNS Server service and holds the necessary records for name resolution. A DNS server will respond to queries coming from DNS clients, it will redirect the Client to another server that will resolve the query or will respond with an information about the requested record (not available or not found). To search for a domain name, issue the nslookup [domain name] command from cmd:
nslookup command
When talking about DNS server you will have to know that such server is authoritative for a domain if it holds the records to resolve that particular domain name. A DNS server can be authoritative for multiple domains. For example, the DNS server containing ittrainingday.com records is authoritative for our domain and also for any subdomain like mail.ittrainingday.com or new.ittrainingday.com. Internet DNS root servers are authoritative to all top-level domains like .com, .gov or . org.
DNS Zones – imagine that an authoritative DNS server can host one or many zones. A zone is a portion of one domain namespace that is delegated to a separate entity (that machine is responsible for name resolution for a zone). A DNS server can be authoritative for multiple domain names and subdomains. The records containing delegated servers for a subdomain are named zones files. In a future article I will show you how to configure zones and you will better understand the process of delegation.
DNS Records – these are entries in the DNS database containing mappings between IP address and domain names. We will talk in a future article about the different types of DNS records and you will understand their role.
DNS Resolvers – in Windows, a DNS resolver is a service that uses the DNS protocol to query for domain names to a remote DNS server or in the local DNS database. By opening the Services console you can view the DNS Client service who is responsible for resolving names and caching DNS information:
DNS Client service
That’s it for this article folks, hope you will enjoy it. Post any comment you think is relevant on this topic.
We will continue talking about the DNS service in the following post so stay tuned for the next article. Don’t forget to check out the latest from Poweradmin also.
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