MacOS配合pfctl实现dnat以及filter
来自三线的随记
摘要
Packet Filter (from here on referred to as PF) is OpenBSD's system for filtering TCP/IP traffic and doing Network Address Translation.
pf是OpenBSD的产物
pf的规则语法非常遵循行为顺序: Rules must be in order: options, normalization, queueing, translation, filtering
通过pf在macOS上实现dnat
1. 首先需要允许IP转发
sysctl -w net.inet.ip.forwarding=1
2. 然后这里通过anchor的形式引入自定义规则方便维护， 当然也可以将需要的规则直接写入/etc/pf.conf文件中，注意macOS在升级的时候会覆盖/etc/pf.conf文件
touch /etc/pf.anchors/my_anchor
3. my_anchor文件中写入如下规则实现DNAT(pf规则允许定义使用变量)
zt_peer_wanip = 223.5.5.5 zt_peer_wanport = 21089 ## 将发往114.114.114.114 9988端口的udp报文DNAT到114.114.114.114:53 rdr pass on lo0 proto udp from any to 114.114.114.114 port 9988 -> 114.114.114.114 port 53 ## 通过变量的形式定义DNAT规则 rdr pass on lo0 proto udp from any to $zt_peer_wanip $zt_peer_wanport -> $zt_peer_wanip port 53 # change route to local interface pass out route-to lo0 proto udp from any to 114.114.114.114 port 9988 # 通过变量的形式定义重路由规则 pass out route-to lo0 proto udp from any to $zt_peer_wanip port $zt_peer_wanport
4. 将/etc/pf.conf文件改写以加载anchor(下文所示规则中一部分的规则是macOS原有的规则，保留不动)
# # Default PF configuration file. # # This file contains the main ruleset, which gets automatically loaded # at startup. PF will not be automatically enabled, however. Instead, # each component which utilizes PF is responsible for enabling and disabling # PF via -E and -X as documented in pfctl(8). That will ensure that PF # is disabled only when the last enable reference is released. # # Care must be taken to ensure that the main ruleset does not get flushed, # as the nested anchors rely on the anchor point defined here. In addition, # to the anchors loaded by this file, some system services would dynamically # insert anchors into the main ruleset. These anchors will be added only when # the system service is used and would removed on termination of the service. # # See pf.conf(5) for syntax. # # # com.apple anchor point # scrub-anchor "com.apple/*" nat-anchor "com.apple/*" nat-anchor my-redirect rdr-anchor "com.apple/*" rdr-anchor my-redirect dummynet-anchor "com.apple/*" anchor "com.apple/*" load anchor "com.apple" from "/etc/pf.anchors/com.apple" # my-redirect anchor "my-redirect" load anchor "my-redirect" from "/etc/pf.anchors/my_anchor"
5. 启用pf并加载规则
pfctl -vF all ; pfctl -vef /etc/pf.conf
（临时保存，still wrinting...）
Related commands
通过command传递rule
echo "pass out route-to (lo0 127.0.0.1) proto tcp and port 80 from any to any" | sudo pfctl -ef -
清空所有
pfctl -vF all
从文件中加载规则
pfctl -vf /etc/pf.conf
附
如上文规则example所示，pf结合dnat可以实现很多玩法，而且pf的规则定义能力还是相当强大的甚至规则能够指定到某些user视角上
包括但不限于:
- 在一些网络需要登陆认证才能使用的场所(如麦当劳 星爹爹等)，同时这些网络的53端口是全白名单端口随意通讯的话，可以将你的流量通过53端口转发出去绕过认证(例如如果你有zerotier网络，可以将你的MOON节点流量以及一些有动态公网IP的流量通过53端口转发出去以建立直连通道，然后将未认证网络的设备的默认网关改为你的zt网络当中的其他设备即可绕过认证上网)
- 通过pf实现类似iptables效果的透明代理(将全部80和443端口的流量转发到某些proxy服务上)
- (发挥脑洞..)
