以下pf.conf（FreeBSD 10.3）似乎阻止了所有 IPv6 流量，我不知道为什么。
tcp_inbound = "{ ssh, domain, http, https }"
tcp_outbound = "{ domain, http, https, imaps, smtps }"
udp_services = "{ domain, ntp }"
block all
pass proto udp to any port $udp_services keep state
pass out proto tcp to any port $tcp_outbound keep state
pass in proto tcp to any port $tcp_inbound keep state
# from https://help.github.com/articles/what-ip-addresses-does-github-use-that-i-should-whitelist/
table <github> { 192.30.252.0/22, 2620:112:3000::/44 }
pass out proto tcp to <github> port { ssh } keep …