mac使用pptp的正确方式

环境：macos mojave 10.14.6

尝试的解决方案：

mac自带vpn 结论：已经不支持pptp协议
使用shimo 结论：无用，连接的时候没反应
为了解决不能连接的问题，某老外写的pptp连接工具结论：无用，报错信息和下一步脚本执行结果一样
实用pppd，步骤如下：

1）进入 /etc/ppp/peers/ 目录，创建 test.vpn，此文件名自己取；

2）写入以下内容，根据需要修改；
```
plugin PPTP.ppp
noauth
remoteaddress "------VPN server name or IP address------"
user "------VPN username------"
password "------VPN password------"
redialcount 1
redialtimer 5
idle 1800
# mru 1368
# mtu 1368
receive-all
novj 0:0
ipcp-accept-local
ipcp-accept-remote
refuse-eap
refuse-pap
refuse-chap-md5
hide-password
mppe-stateless
mppe-128
# require-mppe-128
looplocal
nodetach
ms-dns 8.8.8.8
usepeerdns
# ipparam gwvpn
defaultroute
debug
```
3）运行sudo pppd call test.vpn

结论：出错，结果如下：

Sat Feb 29 11:24:47 2020 : publish_entry SCDSet() failed: Success!
Sat Feb 29 11:24:47 2020 : publish_entry SCDSet() failed: Success!
Sat Feb 29 11:24:47 2020 : PPTP connecting to server 'xxx.xxx.xxx.xxx' (xxx.xxx.xxx.xxx)...
Sat Feb 29 11:24:48 2020 : PPTP connection established.
Sat Feb 29 11:24:48 2020 : PPTP set port-mapping for en0, interface: 9, protocol: 0, privatePort: 0
Sat Feb 29 11:24:48 2020 : using link 0
Sat Feb 29 11:24:48 2020 : Using interface ppp0
Sat Feb 29 11:24:48 2020 : Connect: ppp0 <--> socket[34:17]
Sat Feb 29 11:24:48 2020 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x60725c7f> ]
Sat Feb 29 11:24:51 2020 : rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x90775e6> ]
Sat Feb 29 11:24:51 2020 : lcp_reqci: returning CONFACK.
Sat Feb 29 11:24:51 2020 : sent [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x90775e6> ]
Sat Feb 29 11:24:51 2020 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x60725c7f> ]
Sat Feb 29 11:24:51 2020 : rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x60725c7f> ]
Sat Feb 29 11:24:51 2020 : rcvd [CHAP Challenge id=0xf9 <4a44a223bded3c174d9524e514b7b186>, name = "pptpd"]
Sat Feb 29 11:24:51 2020 : sent [CHAP Response id=0xf9 <7fa23ba608c73e19030ab3ac356541de00000000000044442b41d5fa9f4034e4ba1cf873502c4e3e4ca4d86752c1994800>, name = "xx"]
Sat Feb 29 11:24:51 2020 : rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x241bc6d7> ]
Sat Feb 29 11:24:51 2020 : sent [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x330e8a78> ]
Sat Feb 29 11:24:51 2020 : lcp_reqci: returning CONFACK.
Sat Feb 29 11:24:51 2020 : sent [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x241bc6d7> ]
Sat Feb 29 11:24:51 2020 : rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x60725c7f> ]
Sat Feb 29 11:24:51 2020 : rcvd [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x330e8a78> ]
Sat Feb 29 11:24:51 2020 : rcvd [CHAP Challenge id=0xf1 <7152e60444448f03c00d77bc4f4f85e7>, name = "pptpd"]
Sat Feb 29 11:24:51 2020 : sent [CHAP Response id=0xf1 <67c6ba6d36b2fcf0f07d2b24d38a13db000000000000000099b744446dee24113587aab45c859bc033099f424d94e50400>, name = "xx"]
Sat Feb 29 11:24:51 2020 : rcvd [CHAP Success id=0xf1 "S=21E481AFF77DB980039418F738D7749C6A4C590A M=Access granted"]
Sat Feb 29 11:24:51 2020 : sent [CCP ConfReq id=0x1 <mppe +H -M +S -L -D -C>]
Sat Feb 29 11:24:51 2020 : rcvd [CCP ConfReq id=0x1 <deflate 15> <deflate(old#) 15>]
Sat Feb 29 11:24:51 2020 : MPPE required but peer negotiation failed
Sat Feb 29 11:24:51 2020 : sent [LCP TermReq id=0x3 "MPPE required but peer negotiation failed"]
Sat Feb 29 11:24:51 2020 : Connection terminated.
Sat Feb 29 11:24:51 2020 : sent [CCP ConfRej id=0x1 <deflate 15> <deflate(old#) 15>]
Sat Feb 29 11:24:51 2020 : PPTP disconnecting...
Sat Feb 29 11:24:51 2020 : PPTP clearing port-mapping for en0
Sat Feb 29 11:24:51 2020 : PPTP disconnected

可以发现，报错信息在这里：

MPPE required but peer negotiation failed

多方搜索无果，只能靠自己了......

再次打开 test.vpn 配置文件，我发现了其中关于 mmpe 的部分：
```
mppe-stateless
mppe-128
# require-mppe-128
```
发现问题所在了吗？我搜索到的所有教我配置pppd配置文件中的内容都是这样，但是报错却提示“MPPE required but peer negotiation failed”，因此，我尝试将另外两行和mmpe相关的配置行注释掉，结果如下：
```
# mppe-stateless
# mppe-128
# require-mppe-128
```
再次执行 sudo pppd call test.vpn，错误解决，运行成功！！

如图，运行成功后，最下面两行是这样：

mac使用pptp的正确方式

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