Skip to main content This browser is no longer supported. Show Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. Reviewing DNS Concepts
In this article
Domain Name System (DNS) is a distributed database that represents a namespace. The namespace contains all of the information needed for any client to look up any name. Any DNS server can answer queries about any name within its namespace. A DNS server answers queries in one of the following ways:
It is important to understand the core features of DNS, such as delegation, recursive name resolution, and Active Directory-integrated DNS zones, because they have a direct impact on your Active Directory logical structure design. For more information about DNS and Active Directory Domain Services (AD DS), see DNS and AD DS. DelegationFor a DNS server to answer queries about any name, it must have a direct or indirect path to every zone in the namespace. These paths are created by means of delegation. A delegation is a record in a parent zone that lists a name server that is authoritative for the zone in the next level of the hierarchy. Delegations make it possible for servers in one zone to refer clients to servers in other zones. The following illustration shows one example of delegation. The DNS root server hosts the root zone represented as a dot ( . ). The root zone contains a delegation to a zone in the next level of the hierarchy, the com zone. The delegation in the root zone tells the DNS root server that, to find the com zone, it must contact the Com server. Likewise, the delegation in the com zone tells the Com server that, to find the contoso.com zone, it must contact the Contoso server. Note A delegation uses two types of records. The name server (NS) resource record provides the name of an authoritative server. Host (A) and host (AAAA) resource records provide IP version 4 (IPv4) and IP version 6 (IPv6) addresses of an authoritative server. This system of zones and delegations creates a hierarchical tree that represents the DNS namespace. Each zone represents a layer in the hierarchy, and each delegation represents a branch of the tree. By using the hierarchy of zones and delegations, a DNS root server can find any name in the DNS namespace. The root zone includes delegations that lead directly or indirectly to all other zones in the hierarchy. Any server that can query the DNS root server can use the information in the delegations to find any name in the namespace. Recursive name resolutionRecursive name resolution is the process by which a DNS server uses the hierarchy of zones and delegations to respond to queries for which it is not authoritative. In some configurations, DNS servers include root hints (that is, a list of names and IP addresses) that enable them to query the DNS root servers. In other configurations, servers forward all queries that they cannot answer to another server. Forwarding and root hints are both methods that DNS servers can use to resolve queries for which they are not authoritative. Resolving names by using root hintsRoot hints enable any DNS server to locate the DNS root servers. After a DNS server locates the DNS root server, it can resolve any query for that namespace. The following illustration describes how DNS resolves a name by using root hints. In this example, the following events occur:
Resolving names by using forwardingForwarding enables you to route name resolution through specific servers instead of using root hints. The following illustration describes how DNS resolves a name by using forwarding. In this example, the following events occur:
FeedbackSubmit and view feedback for Which type of DNS server responds to users query?Recursive DNS resolver: A recursive DNS resolver is the DNS server that responds to the DNS query and looks for the authoritative name server or a cached DNS result for the requested name.
What are the three 3 types of DNS queries?3 types of DNS queries—recursive, iterative, and non-recursive.
What is a DNS name query?A DNS query (also known as a DNS request) is a demand for information sent from a user's computer (DNS client) to a DNS server. In most cases a DNS request is sent, to ask for the IP address associated with a domain name.
What are DNS responses?DNS is a query/response protocol. The client queries an information (for example the IP address corresponding to www.google.com) in a single UDP request. This request is followed by a single UDP reply from the DNS server. DNS uses UDP port 53 to connect to the server.
|