System Administration(SAD622S) Name of Presenter: Shadreck Chitauro Lecturer 18 July 2016 Faculty of Computing and Informatics

Contents 1.DNS Overview and Benefits 2.DNS Namespace 3.Top Level Domains 4.Second Level Domains 5.Naming Subdomains 6.DNS Resolver and Resource Records 7.DNS Zones and Zone Types 8.DNS Root Hints File 9.DNS Primary and Secondary Server 10.DNS Caching-only, DNS Forwarder and Secure Dynamic Updates 11.DNS Tools for Troubleshooting Faculty of Computing and Informatics

DNS Overview DNS provides a method of naming computers and network services using a hierarchy of domains When a user enters a user-friendly DNS name in an application, DNS services can resolve the name to other information associated with the name, such as an IP address For example, it’s easy for most users who want to locate a computer on a network to remember and learn a friendly name such as DNS Overview

Faculty of Computing and Informatics DNS Overview Computers communicate over a network by using numeric addresses DNS provides a way to map the user-friendly name for a computer or service to its numeric address If you have used a Web browser, you have used DNS Active Directory uses DNS as its domain naming and location service DNS Overview

Faculty of Computing and Informatics DNS Benefits DNS names are user-friendly, which means they are easier to remember than IP addresses DNS names remain more constant than IP addresses; An IP address for a server can change, but the server name remains the same. DNS allows users to connect to local servers using the same naming convention as the Internet DNS Benefits

Faculty of Computing and Informatics The DNS Namespace The DNS namespace is a hierarchical space A hierarchy is defined as a structure in which an entity is subordinate to the entity above it Many of us are familiar with hierarchies such as the military, where a private is subordinate to a corporal, who is subordinate to a sergeant, and so forth In the DNS hierarchy, the DNS name is divided into separate levels, each denoted by a dot or period (.) The DNS Namespace

Faculty of Computing and Informatics The DNS Namespace The top of the hierarchy is the right-most part of the name and the lowest level of the hierarchy is the left-most part of the name Every node in the hierarchy has a name, referred to as a label, which can be zero to 63 nodes or characters. The domain name for a specific node is the list of labels along the path from the root to the specific node The full list of labels for a particular node is referred to as a FQDN (Fully Qualified Domain Name) The DNS Namespace

Faculty of Computing and Informatics The DNS Namespace It is considered fully qualified because the entire list of labels is shown, leaving no doubt as to the entire path through the hierarchy to the specific node Since we read domain names from left to right, we start with the most specific name and move up the hierarchy toward the more generic top level domain (TLD) The DNS Namespace

Faculty of Computing and Informatics Top Level Domains The root domain is denoted with the use of a dot (.) and has a length of zero characters and it marks the start of any domain e.g. polytechnic.edu.na. After the root, we move to the left, to the Top Level Domains (TLD) There are three types of TLDs: ARPA, Generic, and Country Codes There were originally seven generic TLDs, as defined in RFC 1034: com, net, org, edu, mil, gov, and int. Top Level Domains

Faculty of Computing and Informatics Original Top Level Domains Designations

Faculty of Computing and Informatics New Generic Top Level Domains

Faculty of Computing and Informatics Second Level Domain Less specific than the TLDs are the second-level domain names These identify specific organizations and must also be unique within their respective TLDs on the Internet The uniqueness is regulated to ensure that the combination of second-level domain name plus TLD is always unique Second Level Domain

Faculty of Computing and Informatics Naming Subdomains Subdomains are below second-level domain names, and there can be multiple subdomains below the secondary level The subdomains beginning at the third level are to the left of the organizationally specific second-level domain name Subdomains are not regulated by any central authority and each organization or company is free to use whatever subdomain naming structure it chooses, since the second-level and top-level domains are regulated to ensure uniqueness Subdomain names can be duplicated at other organizations but cannot be duplicated within the same second-level domain Naming Subdomains

Faculty of Computing and Informatics DNS Resolver DNS resolvers are programs that use DNS queries to request information from DNS servers. A resolver usually is built into a utility program or can be made accessible via Library functions and can communicate with a remote DNS server or the DNS server running locally A resolver can be run on any computer, including on a computer acting in the role of DNS server DNS Resolver

Faculty of Computing and Informatics Resource Record Resource records are sets of information used to resolve name resolution queries A DNS server contains the resource records it needs to respond to name resolution queries for the namespace for which it is authoritative Resource Record

Faculty of Computing and Informatics DNS Zones A zone is a contiguous portion of the domain name space for which a DNS server is authoritative A zone is not a domain A domain is a branch of the namespace A zone is a portion of a namespace that can contain multiple domains DNS Zones

Faculty of Computing and Informatics DNS Zone Files Zone files are files that contain resource records for the zone for which the DNS server is authoritative Typically, zone files are text files In Windows Server 2003/2008/2012, they can also be stored in the Active Directory database DNS Zone Files

Faculty of Computing and Informatics DNS Zones A DNS server is authoritative over one or more zones, meaning it maintains the database of resource records related to the nodes in the zone(s) for which is it responsible (or authoritative) Zones can be either primary or secondary A primary zone is the copy of the zone to which updates are made A DNS server that is authoritative for a particular zone will make updates to the primary zone DNS Zones

Faculty of Computing and Informatics DNS Zones A secondary zone is a copy of the zone that is copied from the master server when replication of the zone occurs via zone transfer A primary zone cannot be managed by two different DNS servers, except that multiple computers can be configured to manage zones that are integrated into Windows Active Directory A zone transfer is when the zone resource records are replicated DNS Zones

Faculty of Computing and Informatics DNS Zone Types

Faculty of Computing and Informatics DNS Resource Record Types

Faculty of Computing and Informatics DNS Root Hints File The root hints file holds host information needed to resolve names outside of the authoritative DNS domains This file, also called the cache hints file, contains names and addresses of root DNS servers, typically found on the Internet If your network is connected to the Internet, the root hints file should contain the addresses of the root DNS servers on the Internet If your network is not connected to the Internet, the file should contain the address of the DNS root server within your network DNS Root Hints File

Faculty of Computing and Informatics DNS Standard Primary Server The standard primary DNS server contains the zone database for which it is authoritative This zone has a SOA RR and a NS RR that specifies it as the primary zone Any changes to the zone’s RRs, including delegation of a portion of the zone to another DNS server, are made on the primary DNS server DNS Standard Primary Server

Faculty of Computing and Informatics DNS Standard Secondary Server A standard secondary DNS server is one that contains a copy of the primary DNS server’s zone database It is replicated via a process called zone transfer Many organizations configure secondary DNS servers to provide fault tolerance If the primary DNS server is down, name resolution can be handled by the secondary DNS server(s) until the primary DNS server is restored DNS Standard Secondary Server

Faculty of Computing and Informatics DNS Caching-only Server As the name implies, caching-only DNS servers perform queries and store the results They are not authoritative for any zones and they do not host any zones The only data a caching-only DNS server stores is data it has collected via name resolution queries DNS Caching-only Server

Faculty of Computing and Informatics DNS Forwader Much like a stud zone, a forwarder configures your DNS server to send DNS queries to a specific server for a specific domain DNS Forwarder

Faculty of Computing and Informatics DNS Secure Dynamic Updates Windows Server 2003/2008/2012 supports the dynamic update protocol which allows hosts to dynamically register their names in the DNS database, reducing the administrative overhead associated with manual updates When DNS zone information is stored in Active Directory, DNS is automatically configured to accept dynamic updates DNS Secure Dynamic Updates

Faculty of Computing and Informatics DNS Tools for Troubleshooting Nslookup.exe Nltest.exe Ipconfig.exe Dnscmd.exe Dnsclient.exe Dnslint Dcdiag DNS Tools for Troubleshooting

Faculty of Computing and Informatics DNS Server >>> END <<< DNS Server

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