FreeBSD如何设置基本防火墙规则？

本示例代码介绍了如何在FreeBSD系统上使用ipfw和pf工具来设置基本的防火墙规则。采用了deny-by-default策略，只允许某些特定的流量通过，保护系统免受未经授权的访问。实现方式简明易懂，适合初学者学习和实践。

# enable firewall at boot time:
echo 'firewall_enable="YES"' >> /etc/rc.conf

# set up basic deny-by-default rules with ipfw:
ipfw flush # clean old rules
ipfw add 00100 deny all from any to any # deny all by default
ipfw add 00200 allow tcp from any to any 80 in # allow incoming http connections
ipfw add 00300 allow udp from any to any 53 in # allow incoming dns queries
ipfw add 00400 allow icmp from any to any # allow incoming ping
ipfw add 65535 allow all from any to any # allow all outgoing traffic

# set up basic deny-by-default rules with pf:
echo 'block all' > /etc/pf.conf # deny all by default
echo 'pass in quick proto tcp from any to any port 80' >> /etc/pf.conf # allow incoming http connections
echo 'pass in quick proto udp from any to any port 53' >> /etc/pf.conf # allow incoming dns queries
echo 'pass in quick proto icmp from any to any' >> /etc/pf.conf # allow incoming ping
echo 'pass out all' >> /etc/pf.conf # allow all outgoing traffic
pfctl -f /etc/pf.conf # load the new rules

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