DNS Name Resolution

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DNS resolution is the process of translating a domain name into an IP address.

Initiating

• initiating DNS resolution:
  • user presents an FQDN to an application program (e.g., web browser)
  • client application (called stub resolver) checks its local cache for the mapping
  • if no mapping is cached, it forwards the query to its local name server
  • IP addresses of name servers that can act as resolvers are usually set in the TCP/IP configuration

Process

• most queries between name server are performed as iterative lookups
  • means a name server responds to a query with either:
    • the requested record
    • or the address of a name server at a lower level in the hierarchy that is authoritative for the namespace
  • makes no effort to try to make additional queries to locate information that it does not have
• at steps 4 and 5,
  • root server and .net name server simply pass the querying server the address of an authoritative name server
  • do not take on the task of resolving the original query
• a recursive lookup means that if the queried server is not authoritative,
  • it queries other name servers until it finds the requested record or times out
  • name servers listed in a client’s TCP/IP config accept recursive queries
  • this is the type of query performed by the corp.515support.com name server

Info

• DNS server may be configured to:
  • only perform recursive querying (a resolver)
  • perform recursive querying and maintain zone records
  • or only maintain zone records
• roles are usually split
  • especially if the servers are open to the Internet
• most Internet-accessible DNS servers disable recursive queries
• recursive resolvers are typically only accessible by authorized clients
  • subscribers within an ISP’s network or clients on a private LAN