NAVIGATION

Joseph Crutsinger

Nameserver Concepts
  • Zone
    • A zone is part of the name space ( such as dnsclass.com or bbn.com delegated to a single server: If a nameserver is listed at the internic (or a higher level nameserver as authoritative for parot of the name space, and it has full data on that part of the name space then it is authoritative for that zone.
    Domain
    • A domain is also part of the name space, but it may covers several zones. (ns1.dnsclass.com is a domain that covers both the dnssecondary.com and the testing.com zones)

Domain Delegation

  • Top two levels delegated from the NIC
  • Third level and lower delegated by the site controlling the next higher domain. For Example,
    .com- controlled by the NIC
    .dnclass.com - delegated by the NIC to named.caps.maine.edu
    www.dnsclass.com - delegated by ns1.dnsclass.com to a virtual domain or other domain

Common domain name heirarchy tree.

Resolvers

  • The DNS Client
  • Generates the queries, for domain name information, that are sent to a name server.
  • Completely seperate from the name server function.
  • Configured via /etc/resolv.conf
    ;
    ; Bind Data
    ;
    domain dnsclass.com ; used to fully qualify non canonical DNS requests
    nameserver 10.0.0.2 ; Where are my Nameservers
    nameserver 10.0.0.3 ; and in what order to I query them

Name Servers

  • The DNS Server
    • Answers DNS Queries sent by resolvers
    • Listens at UDP and TCP port 53
      • UDP for routine queries
      • TCP used for zone transfers
  • Configurations
    • Caching-only: relies on other name servers for authoritative answers
    • Primary: Contains the writable authoritative copy for the zones that it is primary for
    • Secondary: Contains mirror copy of the data from a primary nameserver. No updates take place here, used to provide redundancy
Definition of Primary and Secondary Servers:

Primary:
Contains the writable authoritative copy for the zones that it is primary for

Secondary:
Contains mirror copy of the data from a primary nameserver. No updates take place here, used to provide redundancy

Primary VS. Secondary

  • Primary
    • Data loaded from a file.
    • One primary server per zone.
  • Secondary
    • Data transferred from a primary server.
    • Data may be stored in a file.
    • Checks every refresh period with the primary, looking for changes.
    • Might have many secondaries per zone

Some Key points to remember:
  • Hierarchical
  • Dot used as a separator
  • Right-most component is the top-most domain
  • Top-level domain: .edu, .gov, .mil, .com, .arpa, .org, .net + the country domains (.uk, .de, .no, .il, etc...), and the new .us hierarchy
  • FQDN: www.dnsclass.com vs. relative name dnsclass (relative to a default domain, in this case dnsclass.com)