• Firewalls usually check requests coming in 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"
• ..."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

18 / 24