DNS Servers

The Need Of Well Designed And Efficient Name Resolution Services For A Large Scale Network Infrastructure Is Essential For The High Performance Of The Corporate Communication

In simple networking at home that share broadband internet connection with some computers at the household, you might not need a DNS server for name resolution. Name resolution will be forwarded to the ISP where you subscribe the Internet services from. But for your large scale corporate network you need to properly design your name resolution services as efficient as possible.

In windows server 2003, the tools and component in implementing network infrastructure in windows 2003 can fall into the following items:

• TCP/IP and IPV4 or IPV6
• Dynamic Host Configuration Protocol (DHCP)
• Domain Name System (DNS)
• Active Directory (AD)
• Routing and remote Access (see also routing guide)
• Web Services

A DNS server is a computer that runs a DNS server program, such as the DNS Server service or Berkeley Internet Name Domain (BIND). DNS servers contain DNS database information about some portion of the DNS domain tree structure and resolve name resolution queries issued by DNS clients.

DNS servers were originally designed to find the hosts on ARPANET and Stanford Research Institute (SRI) maintained hosts.txt file. If a computer was to added to the network, its information had to be e-mailed to SRI.

Namespace hierarchy

The naming system on which DNS servers is based is a hierarchical and logical tree structure called the DNS namespace. In the root top-level domains are centrally managed, while the second-level domains and below are managed by the owners. Root DNS servers only maintain entries for top level as referral system.

DNS Servers Namespace

Zones / domains

Domains in DNS servers are portion of the namespace that refers to all of the resources within the environment. While zones in DNS servers can be described as follows:

• Portions of the namespace that includes the domain
• One contiguous portion of the namespace for which a server is authoritative. DNS servers can be authoritative for one or more zones, and a zone can contain one or more contiguous domains.
• Represented by a file stored on the DNS server. Zone files contain resource records for the zones for which a server is authoritative. In many DNS servers implementation, zone data is stored in text files; however, DNS servers running on Windows 2000 or Windows Server 2003 domain controllers can also store zone information in Active Directory.
• Initially stores all information about one domain

DNS Resolver

A DNS resolver is a service that uses the DNS protocol to query for information from DNS servers. DNS resolvers communicate with either remote DNS servers or the DNS servers program running on the local computer. In Windows Server 2003, the function of the DNS resolver is performed by the DNS Client service. Besides acting as a DNS resolver, the DNS Client service provides the added function of caching DNS mappings.

See also DNS forwarding

Resource Records

Resource records are DNS database entries that are used to answer DNS client queries. DNS servers contain the resource records it needs to answer queries for its portion of the DNS namespace.

• Host address (A), make up the majority of resource records in a zone database of DNS servers which is used to associate computers (hosts) to their IP addresses.
• Alias (CNAME) – commonly called canonical name, allows you to use more than one name to point to a single host.
• Mail exchanger (MX) in DNS servers, is used by email applications to locate a mail server within a zone.
• Pointer (PTR) in DNS servers, is used in reverse lookup zone which perform queries to resolve IP addresses to hosts names or FQDNs (fully qualified domain name)
• Service location (SRV) is used to specify the location of specific services in a domain.

Delegation

It is likely impossible to manage a large scale namespace such as the Internet without delegating the administration of domains. Through the delegation process, a new zone is created when the responsibility for a sub-domain within a DNS namespace is assigned to a separate entity. This separate entity can be an autonomous organization or a branch within your company.

Delegation of sub-domains in DNS servers physically separates DNS records into separate file.

DNS Servers Delegation

When to Delegate Zones?

You should consider delegating a zone within your network whenever any of the following conditions are present:

• You need to delegate management of a DNS domain to a branch or department within your organization.
• You need to distribute the load of maintaining one large DNS database in DNS servers among multiple name servers to improve name resolution performance and fault tolerance.
• You need hosts and host names to be structured according to branch or departmental affiliation within your organization.

DNS servers type

Types of DNS servers refer to the type of zone the server is hosting-or, in the case of caching-only servers, whether it is hosting a zone at all.

• Primary name server
  • Stores main copy of zone file for that zone, zone’s central point of update.
  • Changes / updates made to a zone are made on the primary server
  • With windows 2003, you can deploy primary zones as standard primary zones or primary zones integrated with active directory.
• Secondary name server – a recommendation in DNS design specifications, provide a means to offload DNS query traffic in areas of the network where a zone is heavily queried and used.
  • Backup copy of zone file if a primary server is down
  • Stored in physically separate area
  • Creates a pointer to the primary name server and periodically does a zone transfer
• Caching name server
  • Do not host any zones
  • Not authoritative for any zone
  • Cached lookups, limited to what has been cached while resolving queries
  • Performs DNS queries and stores results

In a Berkeley Internet Name Domain (BIND) environment, primary name servers are often referred to as master name servers while secondary name servers are referred to as slave name servers.

Check also

• configuring the network in your computer networking infrastructure.
• DNS command in DOS command lines
• Setting Up DNS server