DNS Requests

• DNS clients (all hosts) must run a DNS resolver

• • The resolver is linked into each application via a DLL
  • It presents an API to user programs
  • Given an domain name or an IP address, it will request a lookup or a reserve-lookup, respectively, from the local name server

• DNS requests are handled either iteratively or recursively

• • Iterative
  • • Each name server responds directly to the client with either the final answer or the IP address of another name server that should know the answer
    • It is up to the client to query the next name server
  • Recursive
  • • The local name server determines the answer by iteratively or recursively querying other name servers
  • Results may be cached