Firewall – outbound ports that are always open

firewallinternetnetworkingport

What are some ports that can NEVER be blocked outbound in firewalls, as doing so will stop basic internet use?
Some I can think of are:
port 53 udp/tcp — dns, blocking this will prevent users accessing any domain
port 80 tcp – http
port 443 tcp – https
Are these all, and are these ports ALWAYS accessible outbound on every host connected to the internet?

Best Answer

There are no ports that need to be opened for full access in your outbound firewall rules.

Why? Because by proxying requests we can achieve the same thing, except with more control.

The three most common:

  • HTTP proxy (so you can close port 80 and 443)
  • Internal DNS servers (proxy requests to the outside world)
  • Internal Mail server (relays incoming and outgoing mail to the world)

Then you simply setup your firewall to allow connections from the IPs associated with the machines running these services ONLY.

Basically, it's a subjective question with no real right answer.

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