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Resolving Names
Graeme Mathieson <mathie@woss.name>
Blog: https://woss.name/
Twitter: @mathie
Domain Name System
(DNS)
–Phil Karlton
“There are only two hard things in Computer
Science: cache invalidation and naming things.”
A Sneak Peek at The
Internet
http://the-internet.woss.name/

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Resolving names

Editor's Notes

  1. DNS involves both.
  2. Local resolver Machinations underneath gethostbyname() Checks local cache and /etc/hosts Knows the IP address of a name server (via DHCP or static configuration) Sends the request off to the name server and waits for a response Recursive name server: Often first hop is your home router Responds from its local cache if possible If not, it attempts to resolve the address by: Querying its upstream (ISP name server?) Querying the root servers (well known IP addresses)
  3. Root server 13 well-known IP addresses of root servers Really hundreds of machines distributed globally Authoritative for the root zone Knows the authoritative name server for .com, .net, .uk, etc. Ask for the A record for woss.name Doesn’t know the answer, but knows where to ask next Returns a list of NS records for . name Also returns a list of A records for the name servers in .name Glue records
  4. Authoritative name server for .name Ask for the A record for woss.name Doesn’t know the answer for the A record Knows which servers to ask next Returns the NS records for woss.name No glue records this time, so recursive server has to look up kara.ns.cloudflare.com
  5. Finally, an authoritative server for woss.name Asks for an A record for woss.name This server is authoritative Returns the A record for woss.name
  6. Recursive name server: Receives the response for woss.name Caches it Returns the query back to the client Client: Receives the result. Caches it Returns the DNS lookup to the application that requested it. All happens before a web request even begins.