• Firewalls usually check requests and either pass, reject, or drop them
  • Usually look at source IP and port number
  • A way to say "people on the internet can access this web server"
  • ..."but people need to be on the network to try to log in with SSH"
  • ..."and these specific people can't come in at all"
  • ..."and these unused ports should not be used"
  • Comes from construction terminology
  • Need firewall rules to allow incoming connections

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