Name Resolution with DNS by liaoxiuli


									Presented by Joe Gigliotti
           & Ben Lodsin
   RFC 1034 (November 1987)
    ◦ Concepts and Facilities
      Introduction to the system and its components
      Explains the concepts of the Domain Name Space and
   RFC 1035 (November 1987)
    ◦ Implementation and Specification
      Details of protocols and algorithms
   Invented in 1983, shortly after TCP/IP
   Developers: Jon Postel and Paul Mockapetris
   Replaced the HOSTS.txt deployment system, a
   Since its original development, there have
    been multiple revisions
   DNS, while useful, has major security flaws
    because of its need for constant record
    changes and updates.
   Short for Domain Name System, DNS’s sole
    purpose is to resolve hostnames (Domain
    Names) to IP Addresses.
   Works as a hierarchy system, a system with
    “chains of command” and resolution
   Referred to as the worlds largest distributed
    database system.
   While not needed for communication
    functionality, DNS helps provide resources to
    services using human readable names.
   The domain name space consists of a tree of
    domain names.
   Top Level Domains (TLD) consist of the
    following, among many others.
    ◦   Com.
    ◦   Org.
    ◦   Net.
    ◦   Edu.
    ◦   Gov.
    ◦   Mil.
   Each zone master is responsible for the
    namespace levels of itself, and all child
   A system administrator can let another
    control part of the name space within his
    zone authority.
   This splits the zone into two multiple,
    dependent but independent, zones.
   A domain name usually consists of two or more
    labels. For example,
   The rightmost label conveys the top-level
    domain. For example, the address has the top level domain com.
   Each label to the left specifies a subdivision,
    known as a subdomain.
 comprises a subdomain of the com
    domain, and comprises a
    subdomain of the domain
   Subdivisions can theoretically go 127 levels deep.
   In this example, the DNS recursor consults three
    name servers to revolved the address
   A DNS resolver interactively queries a root name
    server, org. and name server in its
    quest to revolve the IP address associated with
    the domain name
   Device checks its hosts file (if present) then
    checks its local cache.
   If the lookup doesn’t exist, the device uses its
    configured DNS servers to send out a request
    for a resolution.
   If the DNS server being asked holds a record
    for the domain name, it sends it back. If not,
    it refers to the TLD’s root server.
   The TLD server provides the address of the
    name server holding the record for the
    domain name.
   The client sends a request to the name server
    for the desired record of the domain name.
   The name server responds with the requested
    record holding the IP Address associated with
    the domain name.
   Using the provided resolution, the device
    access the network service using the
    discovered IP Address.
   Reverse lookups are essentially the same as
    normal query's.
   Instead of trying to find an IP address
    associated with a domain, DNS uses PTR
    records to associate a domain with IP
   This allows for circular references to network
    resources and also helps validity of the
    response lookup.
   TTL is an acronym for Time to Live
   In order to help elevate stress on the vast amount
    of lookups of the same domain, domain
    servers/clients Cache their lookup using the TTL
   This means that once is resolved
    from a network device, it is locally kept until it is
   By doing this, the same lookup doesn’t need to
    be completed again and consume bandwidth and
   The same technique is used for ARP, RIP, and
    other network protocols.
   "Howstuffworks "How Domain Name Servers Work""
    HowStuffWorks.Com. 02 May 2008

   "The Lazy Admin: DNS Tips #15 - DNS Resolution Explained." The
    Lazy Admin. 28 Apr. 2008

   "Understanding DNS." 23 May 1997. 03 May 2008

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