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Old 14th September 2010
spaghetti_bolognese spaghetti_bolognese is offline
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Default Help needed with PF ruleset

I'm learning PF firewall for now and I'm looking at OpenBSD's page on PF.

I'm looking at the example and there's this line that I don't quite understand.

pass in on egress inet proto tcp from any to (egress) \
    port $tcp_services
I'm not sure if I understand this correctly, but I think that the bolded part meant that this rule will allow any TCP protocol traffic from egress (external outgoing interface) from any source. However, I don't get the subsequent part.

(egress) \
    port $tcp_services
Could someone please explain it to me?

Kind regards and thanks in advance.
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Old 14th September 2010
ocicat ocicat is offline
Join Date: Apr 2008
Posts: 3,287

Originally Posted by spaghetti_bolognese View Post
..I don't get the subsequent part.

(egress) \
    port $tcp_services
Could someone please explain it to me?
  • The parentheses about the external interface name indicates that the interface's IP address can change -- meaning that the address is set by an external DHCP server.
  • $tcp_services is a list which will have been previously defined. By the name, this must be a list of port numbers which are allowed to pass through the firewall.
Be aware that development on pf(4) has been rapid over the last few years. The syntax of rules have changed such that rulesets created for older versions of OpenBSD may no longer be valid. Because of this, it is important to match the documentation to whatever is installed. Always consider the pf(4) manpage the best source of information matched to the installed version. If the installed version is the latest publicly released version (currently OpenBSD 4.7), information found on the The OpenBSD Packet Filter guide is the second best source of information.
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