Domain Name System - PowerPoint PPT Presentation

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Domain Name System


* Alternate DNS Server Configuration The Preferred and Alternate Servers ... resolver queries DNS servers listed in the TCP/IP properties. * Client Configuration ... – PowerPoint PPT presentation

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Title: Domain Name System

Domain Name System
Domain Name System
  • DNS is a client/server protocol which provides
    Name to IP Address Resolution.

DNS Terms And Concepts
  • Domain Name Space
  • Fully Qualified Domain Name (FQDN)
  • DNS Server
  • DNS Client (Resolver)
  • Query
  • Recursive
  • Iterative
  • DNS Zone Types
  • DNS Record Types
  • DNS Forwarder
  • Client Configuration

DNS Name Space
  • A DNS Namespace is a hierarchical tree in which
    each node represents a named domain
  • Each level of the domain namespace is separated
    by a period
  • The first level of the tree is where youll find
    the top-level domains which form the base of the
    DNS namespace.

DNS Name Space
FQDN DC01.Sales.South.Consoso.COM.
  • DNS Server
  • A computer running the Domain Naming System (DNS)
  • Hosts a namespace or portion of a namespace
  • Is authoritative for a namespace or Domain
  • Resolves name resolution requests submitted by
    DNS Clients (DNS ClientResolver)

owns name space and therefore
is authoritative to that space.
Authoritative NO. I own this space and there
is no record
owns name space and therefore
is authoritative to that space.
owns namespace not
authoritative to therefore sends
query to another DNS server
Recursive Query
  • Client Side
  • The DNS Client typically issues a Recursive Query
    to its configured name server
  • This says, in effect, dont return until you
    have an answer or have failed to find an answer
    to the query.
  • Server Side
  • When the Server receives a Recursive Query,
    unless Recursion is disabled, server goes to
    work for the client.
  • Queries other name servers until it resolves
    clients query, or fails to do so.
  • Responds to client with resolved address or
    failure message.

Iterative Query
  • Asks for Final Answer or Closer Server
  • Typically used between servers during resolution
    of client requests
  • Lower-level server will issue Iterative queries
    to top-level servers
  • Reduces workload on top-level servers
  • Response to an Iterative Query
  • Requested address
  • Authoritative No
  • A Referral, if server recognizes the domain name
    being queried and knows a server address for that

DNS Zone Terminology
  • Zone
  • A collection of name/address mappings for hosts
    within a contiguous portion of the DNS namespace
  • Zone Data is maintained on a DNS Server
  • Flat zone file containing lists of mappings
  • Stored in Active Directory database
  • A server is authoritative for a zone if it can
    resolve names and addresses requested by clients
  • In most cases a zone corresponds to a domain,
    subdomain, or contiguous series of domains and

DNS Zone Types
  • Forward Lookup Zone
  • Resolves Names to IP Address
  • A (Host) Record
  • SRV
  • Etc.
  • Reverse Lookup Zone
  • Resolves IP Addresses to Host Names
  • PTR (Pointer) Records

The Root or dot (.) Zone
This DNS server that is authoritative for the
Root Zone owns the entire namespace. It is the
top of the hierarchy and does not refer to or
forward queries to any other server. This would
be a zone defined within a root hint DNS server
in the top-level domains
Record Types
  • Record Types
  • A (Host)
  • PTR (Pointer)
  • NS (NameServer)
  • SOA (Start of Authority)
  • SRV (Service Record)
  • CNAME (Alias)
  • MX (Mail Exchanger)
  • Etc.

Record Types Defined
  • A (Host)
  • Primary entry for any computer or device on the
  • Resolves host name to IP address
  • PTR (Pointer)
  • Reverse lookup entry, resolves IP Address to host
  • NS (Name Server)
  • Identifies a named host as a DNS Server for a
  • SOA (Start of Authority)
  • Identifies primary DNS name server with
    authority to resolve names for a given zone

Additional Record Types Defined
  • SRV (Service Record)
  • Indicates availability of a given service on a
    given host
  • Example
  • Windows Domain Controllers register SRV Records
    which are used to direct client logon requests
  • CNAME (Alias)
  • Typically relates a well known common name to a
    specific host name.
  • Example
  • WWW is commonly registered as a CNAME record
    for Web servers
  • MX (Mail Exchanger)
  • Identifies E-Mail Servers
  • Example MS Exchange registers an MX record

DNS Forwarder
  • DNS Servers can be configured to forward queries
    to designated Forwarders
  • Forwarders
  • Handle all non-local queries
  • Enabling forwarders allocates burden of resolving
    unknown names to designated server(s)

DNS Client Configuration
  • Client Configuration is Critical
  • Server Addresses
  • DNS Suffix Configuration
  • Dynamic updates
  • Windows clients rely on DNS Name Resolution to
    perform key functions
  • Locate/Connect to DCs for authentication
  • Locate/Connect to Servers
  • Locate/Connect to WebServers

Client Configuration DNS Server Addresses
  • Server Addresses
  • Preferred DNS Server Address
  • Alternate DNS Server Address(es)
  • Sends query to Preferred DNS server
  • Alternate DNS Server used ONLY if Preferred is
    not available.

Preferred DNS Server Configuration
The Preferred DNS Server is the one the client
tries first
If Preferred Server is not available, the client
tries the Alternate DNS Server (if so configured)
Alternate DNS Server Configuration
The Preferred and Alternate Servers specified on
the previous Properties page automatically appear
at the top of this list, and Preferred and
Alternates are queried in order listed
Optionally, you can enter a whole list of
Alternate DNS Servers
Name Query Resolution
  • When a host name is submitted to DNS
  • Resolver first checks the cache (if caching
  • If the name is in the cache, the data is returned
    to the user
  • If name is not in cache, resolver queries DNS
    servers listed in the TCP/IP properties.

Client Configuration - DNS Suffixes
  • If the query cannot be resolved as is, then
    suffixes are systematically appended to the name
    in the query
  • Primary DNS Suffix
  • Connection-specific DNS Suffix
  • Domain Suffix Search List
  • Client is configured to use either Primary and
    Connection Specific
  • or
  • Suffix Search List

Configuring Domain Suffixes
Primary DNS Suffix System Properties gt Computer
Name gtChange gt More
Configuring Domain Suffixes
Suffix Selection Option
Domain Suffix Search List
Client uses either Primary and Connection-specific
or Suffix Search List, not both!
Connection-specific Suffix
Nitpicking DNS Naming Terminology
  • Fully Qualified Domain Name
  • Srv1.Sales.Contoso.Com.
  • Terminating period makes it Fully Qualified!
  • Unqualified Multi-label Name
  • Srv1.Sales.Contoso.Com
  • No Period!
  • Single-label Unqualified Name
  • Srv1
  • No domain suffix!
  • No info to qualify name or indicate where in
    the namespace to look for this host

How Suffixes are Applied
  • If client submits FQDN (including period)
  • Resolver uses FQDN Submitted
  • If client submits multi-label unqualified name
    (no period)
  • Resolver adds terminating period and uses that
  • If multi-label name submitted with period fails
    to resolve, or if client submits single-label
    unqualified name (no suffix)
  • Resolver appends specified Suffixes, adds period,
    and keeps trying! The suffixes it appends
    depends on how the DNS Suffix property is

Example Primary Connection-specific setting
  • Resolver appends Primary and Connection-specific
  • Resolver appends Primary Domain Name from System
    Properties gt Computer Name gt Change gt more
  • Resolver devolves domain name from left to
  • Tries Parent of specified domain
  • If that fails, tries Parent of Parent
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