Note that the client firewall doesn’t need to allow incoming traffic on port 80 for this to work. The web client isn’t hosting a web server with HTTP, so the client firewall would block incoming traffic on port 80. However, the firewall that is filtering traffic to the web server needs to allow incoming traffic on port 80. You can apply this same principle for any protocol and port. For example, if you want to allow SMTP traffic, you create a rule on the firewall to allow traffic on port 25. IT professionals modifying access control lists (ACLs) on routers and firewalls commonly refer to this
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