背景：
我有一台实验机器，链接了多个网络（有线、无线），我可能需要不一样网段走不同的网络出口。需要进行一个静态的路由规则配置。
操作：
查看路由表：
netstat -rn
新增静态路由：
sudo route -n add -net 10.0.0.0/8 10.242.100.1
说明：
我们会发现我们查看路由表命令会有一堆的路由，那隔了很久之后我们还记得哪个是静态路由哪个是动态路由吗？
路由表形如：
➜ ~ netstat -nr
Routing tables
Internet:
Destination Gateway Flags Netif Expire
default link#14 UCSg ppp0
default 10.12.16.1 UGScIg en0
default 10.24.24.1 UGScIg en1
1.11.71.20 link#14 UHW3Ig ppp0 121
10.12.16/23 link#4 UCS en0 !
10.12.16.1/32 link#4 UCS en0 !
你会看到一个Flags的字段：
Flags字段的解释为：
1 RTF_PROTO1 Protocol specific routing flag #1
2 RTF_PROTO2 Protocol specific routing flag #2
3 RTF_PROTO3 Protocol specific routing flag #3
B RTF_BLACKHOLE Just discard packets (during updates)
b RTF_BROADCAST The route represents a broadcast address
C RTF_CLONING Generate new routes on use
c RTF_PRCLONING Protocol-specified generate new routes on use
D RTF_DYNAMIC Created dynamically (by redirect)
G RTF_GATEWAY Destination requires forwarding by intermediary
H RTF_HOST Host entry (net otherwise)
I RTF_IFSCOPE Route is associated with an interface scope
i RTF_IFREF Route is holding a reference to the interface
L RTF_LLINFO Valid protocol to link address translation
M RTF_MODIFIED Modified dynamically (by redirect)
m RTF_MULTICAST The route represents a multicast address
R RTF_REJECT Host or net unreachable
r RTF_ROUTER Host is a default router
S RTF_STATIC Manually added
U RTF_UP Route usable
W RTF_WASCLONED Route was generated as a result of cloning
X RTF_XRESOLVE External daemon translates proto to link address
Y RTF_PROXY Proxying; cloned routes will not be scoped
比如我看到我们刚才加入的静态路由规则应该是：
Internet:
Destination Gateway Flags Netif Expire
10 10.242.100.1 UGSc en1
其中的 USGc的S 表示是手动加上去的。
参考资料：
https://apple.stackexchange.com/questions/336888/whats-the-meanings-of-the-routing-tables-data-in-the-mac-os
https://www.analysisman.com/2020/11/macos-staticroutes.html
https://support.justaddpower.com/kb/article/320-adding-a-static-route-to-macos/