McAfee Secure

Understanding DNS Components

Exam: Microsoft 70-642 - Windows Server 2008 Network Infrastructure, Configuring

For managing a DNS Server it is important to acquire knowledge about a few terms. Knowing the components and understanding their functions will help acquire better understanding leading to better manageability of the server. The article briefly discusses the components and the functions.

  • DNS Server: Any computer that provides domain name services acts like a DNS name server irrespective of where the server resides. To explain it with an example, 13 root servers at the top of the DNS tree delegate the TLDs. The referrals for providing the name servers for the TLD are provided by the root servers. The referrals are provided to an authoritative name server for a specified domain.

    A DNS server implementation that supports resource records related to service location and updates that are dynamic in nature is sufficient for providing the name service for an operating system that runs Windows 2000 software and newer versions.

  • DNS Client: A machine that issues queries to a DNS server is a DNS client. Registration of a client hostname may or may not be undertaken in a DNS database. A DNS client is any machine that issues queries to a DNS server. The client hostname may or may not be registered in a DNS database. The DNS requests are issued by the clients through a set of processes termed as resolvers.
  • DNS Server List: While setting up a DNS client, there is a provision for setting up the DNS Server List. The list contains names of those servers that a client can resort to for resolving names.
  • DNS Suffix Search Order: A DNS suffix search order can be set up on a client. The DNS zone name is also the name of the suffix. It is possible to set up multiple suffix names on a client in case there are more than one DNS names. Configuration of a number of DNS client settings can be done through the GPO (Group Policy Object).
  • Resolver: Resolvers are software defined processes that may be implemented in software libraries responsible for handling the real process of locating the answers to the queries for DNS data. A resolver acts as a part of large chunks of software ensuring that the external libraries are not required to be resorted to for making and processing DNS queries. Client computers and other DNS servers that are attempting to resolve an answer on behalf of a client can act like a resolver.
  • Query: A query is a request made to a DNS server for information. There are three types of queries that can be made to a DNS server - iterative, inverse and recursive.
  • Link-Local Multicast Name Resolution (LLMNR): This is a name resolution protocol that follows the peer to peer model. It broadcasts to the hosts that are in the neighborhood for helping resolve hostname issues. It works well with both IPv4 and IPv6. Routers do not pass the LLMNR protocol traffic for the simple reason that it uses broadcasts.
  • DNS Devolution: in case a client computer is a part of childnamespace, the client computer has access to resource which is in the parent namespace by using DNS devolution. DNS devolution explicitly makes provision for fully qualified domain name (FQDNs) of the resource. DNS devolution removes that label of the namespace which is placed left most in order to reach the parent suffix. DNS devolution permits creation of new FQDNs.
  • Record Weighting: Weighting of DNS records permits an administrator to place value on the DNS SRV records. Clients are able to choose randomly SRV records that are proportional to the weight value that has been assigned.
  • Netmask Ordering: In case round robin is enables, a client requests for name resolution. The first address that is entered in the database gets returned to the resolver and is placed at the end in the list. When the next attempt to resolve the name is made, the second name is returned by the DNS server and then placed at the end of the list. Round Robin is a default condition. Netmask ordering is a component of the round robin process. When Netmask ordering is configured, the DNS server detects the subnet of the client that has launched the query. The DNS server then returns the host address that is available for the same subnet.
  • DnsUpdateProxy Group: It is possible to configure the DHCP server for dynamic registration of records related to host (A) and pointer (PTR). It does this on behalf of the DHCP clients. This can result in the DNS server being loaded with resources that are not updated. The DnsUpdateProxy can help resolve this issue.

    For using it, the first step is to create a user account solely for this purpose and configuring the DHCP server with the necessary credentials. This does not allow creation of unsecured records. It also makes it possible to register the records in zones permitting only secured updates.