1. packet_filter

FreeBSDでもOpenBSD由来のpfが使えます。

https://techhub.hpe.com/eginfolib/networking/docs/switches/5980/5200-3903_acl-qos_cr/content/499630541.htm

Inbound vs. outbound firewall rules: What are the differences?

https://www.techtarget.com/searchsecurity/answer/Comparing-firewalls-Differences-between-an-inbound-outbound-firewall

Outbound IP Filters https://support.usr.com/support/9114/9114-ug/security_ipout.html

Ingress_Filtering Egress_Filtering