DNS study notes — Full-service resolver and content server

Introduction

In this post we will cover:

  • Stub resolver
  • Preferred name server and alternate name server
  • Full service resolver and content server
  • Root server

Stub resolver

Client software that makes a request to a name server. When the stub resolver queries the name server for a domain, the domain is usually specified by the FQDN. If only the host name is specified, the stub resolver completes the domain name to create the FQDN. The path completed at this time is called a search path, which is usually the domain to which the host itself belongs.

Preferred name server and alternate name server

Two or more name servers are usually set from the viewpoint of fault tolerance. In addition to registering multiple name servers in the stabilizer , specify the name server that normally inquires ( priority name server ) and the name server that inquires when the preferred name server goes down ( alternative name server ). There may be inconsistencies in cached information (such as not reflecting IP address changes) between multiple name servers. At this time, “whether the name server has the latest cache” and “whether the stub resolver has the latest returned domain information” cannot be determined.

Full service resolver and content server

A name server that returns only zone information that has an Authority is called a content server . This is the root domain or registry name server. On the other hand, a name server that searches a domain from a domain namespace is called a full-service resolver . A full-service resolve will look up in the domain namespace if it doesn’t have the cached information to handle the request. Therefore, the full service resolver needs to know the name server of the root domain.

Root server

There are 13 root domain name servers (root servers) in the world ( A.ROOT-SERVERS.NET~ M.ROOT-SERVERS.NET). The latest root server information is downloaded from IANA as a root hint file. Root hints are named.root managed as in BIND . Of the 13 root servers, the one that the full-service resolver inquires has the shortest response time.

  • The full service resolver has a correspondence table between the root server and the response time.
  • Initially, each response time is set randomly.
  • After that, the server with the shortest response time is inquired, and the correspondence table is updated with the actual response time.

Recursive and iterative queries

A request from a stub resolver to a full-service resolver is called a recursive query, and a request from a full-service resolver to a content server is called an iterative query . The response to a recursive query is one of the following:

  • IP address corresponding to the domain
  • No domain name

The response to the iterative query is one of the following:

  • IP address corresponding to the domain
  • No domain name
  • Name server that seems to know the domain

 by the author.

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