Notes for Computer Information Technology 160
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October 17 - DNS


Ping of Death - when so many pings for the purpose of disruption that no legitimate internet traffic can get through, this was an issue about 15 years ago, and to this day ICMP is still blocked on many university networks


  • Top Level Domains: com, biz, edu, net, etc…
  • .onion is not in the Internet DNS root, but with the the tor binary installed, .onion domain names can be accessed
  • Every time you go up a level you add a dot,
  • = /edu/csun/sandbox/ns1
  • DNS Iterator - looks at HINTS file, searches first from top level domain then lower on the list
  • Every zone file has two DNS servers

Local Setup

Applications like Firefox and the email client do not make dns requests, dns requests happen on the operating system level. It has a DNS resolver and a cache. Sometimes you need to hard refresh to clear the cache.

Local DNS Files

  • /etc/resolve.conf lists the current dns server for resolving dns requests
  • /etc/hosts is a local list of dns entries
  • /etc/nsswitch.conf is the config of the GNU Name Service Switch