我在使用 iptables 和 PPTP VPN 时遇到了问题，我在网上和网上都读过相关主题，但仍然无法让它工作！我试图在我们本地网络上的 ubuntu 服务器上设置 PPTP，以强制客户端必须通过 VPN 登录才能访问互联网。ubuntu 服务器直接连接到互联网。
在我的 rc.local 中，我有以下内容来转发和接受 gre
# PPTP IP forwarding
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A INPUT -p gre -j ACCEPT
sudo iptables -A OUTPUT -p gre -j ACCEPT
它出现在我的 iptables 列表中，所以我知道它在那里。
我在服务器上使用 CSF 作为防火墙，如果禁用它，我可以连接到 VPN 并通过它浏览互联网，如果启用了 CSF，我要么“被通信设备断开连接”，要么我可以连接但无法通过 VPN 访问互联网。
这也有一个奇怪的问题，即它时不时似乎可以通过防火墙工作！
我打开了以下端口：
TCP_IN = ...47,53,80,92,110,143,443,465,587,993,995,1723,7777..
TCP_OUT = ...47,53,80,92,110,113,443,1723,25565,7777...
UDP_IN = 20,21,47,53,1723,27015,27025
UDP_OUT = 20,21,47,53,113,123,1723,27015, 27025
您对如何解决此问题有什么建议吗？您是否需要更多信息？
非常感谢你的宝贵时间，
根据要求提供的额外信息：
iptables -nvL
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
7377 749K LOCALINPUT all -- !lo * 0.0.0.0/0 0.0.0.0/0
5631 786K ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT udp -- !lo * 130.88.13.7 0.0.0.0/0 udp spts:1024:65535 dpt:53
0 0 ACCEPT tcp -- !lo * 130.88.13.7 0.0.0.0/0 tcp spts:1024:65535 dpt:53
3 626 ACCEPT udp -- !lo * 130.88.13.7 0.0.0.0/0 udp spt:53 dpts:1024:65535
0 0 ACCEPT tcp -- !lo * 130.88.13.7 0.0.0.0/0 tcp spt:53 dpts:1024:65535
0 0 ACCEPT udp -- !lo * 130.88.13.7 0.0.0.0/0 udp spt:53 dpt:53
0 0 ACCEPT udp -- !lo * 130.88.149.93 0.0.0.0/0 udp spts:1024:65535 dpt:53
0 0 ACCEPT tcp -- !lo * 130.88.149.93 0.0.0.0/0 tcp spts:1024:65535 dpt:53
431 71632 ACCEPT udp -- !lo * 130.88.149.93 0.0.0.0/0 udp spt:53 dpts:1024:65535
0 0 ACCEPT tcp -- !lo * 130.88.149.93 0.0.0.0/0 tcp spt:53 dpts:1024:65535
0 0 ACCEPT udp -- !lo * 130.88.149.93 0.0.0.0/0 udp spt:53 dpt:53
5021 561K INVALID tcp -- !lo * 0.0.0.0/0 0.0.0.0/0
4255 519K ACCEPT all -- !lo * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:20
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:21
1 64 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:47
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:53
61 3648 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:80
1 64 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:92
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:110
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:143
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:389
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:443
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:465
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:587
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:993
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:995
3 192 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:1723
2 128 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:7777
89 5340 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25565
84 5040 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:27015
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:21433
103 6180 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25566
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:23456
0 0 ACCEPT tcp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:6667
0 0 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:20
0 0 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:21
0 0 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:47
0 0 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:53
0 0 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:1723
435 19275 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:27015
389 16837 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:27025
0 0 ACCEPT udp -- !lo * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:6667
2 122 ACCEPT icmp -- !lo * 0.0.0.0/0 0.0.0.0/0 icmp type 8 limit: avg 1/sec burst 5
0 0 ACCEPT icmp -- !lo * 0.0.0.0/0 0.0.0.0/0 icmp type 0 limit: avg 1/sec burst 5
0 0 ACCEPT icmp -- !lo * 0.0.0.0/0 0.0.0.0/0 icmp type 11
0 0 ACCEPT icmp -- !lo * 0.0.0.0/0 0.0.0.0/0 icmp type 3
1127 73207 LOGDROPIN all -- !lo * 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
8150 710K LOCALOUTPUT all -- * !lo 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT tcp -- * lo 0.0.0.0/0 0.0.0.0/0 tcp dpt:25
0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 owner GID match 8
0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 owner UID match 0
123 7380 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25
5631 786K ACCEPT all -- * lo 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 tcp dpt:53
436 32454 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 udp dpt:53
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 tcp spt:53
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 udp spt:53
6572 649K INVALID tcp -- * !lo 0.0.0.0/0 0.0.0.0/0
6852 636K ACCEPT all -- * !lo 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:20
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:21
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:47
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:53
148 8880 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:80
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:92
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:110
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:113
2 120 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:389
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:443
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:1723
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25565
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:7777
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:27015
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:21433
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:23456
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:3306
30 1800 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:2082
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:92
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25555
0 0 ACCEPT tcp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:6667
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:20
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:21
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:47
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:53
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:113
52 3952 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:123
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:1723
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:27015
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:27025
0 0 ACCEPT udp -- * !lo 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:6667
0 0 ACCEPT icmp -- * !lo 0.0.0.0/0 0.0.0.0/0 icmp type 0
0 0 ACCEPT icmp -- * !lo 0.0.0.0/0 0.0.0.0/0 icmp type 8
0 0 ACCEPT icmp -- * !lo 0.0.0.0/0 0.0.0.0/0 icmp type 11
0 0 ACCEPT icmp -- * !lo 0.0.0.0/0 0.0.0.0/0 icmp type 3
3 183 LOGDROPOUT all -- * !lo 0.0.0.0/0 0.0.0.0/0
Chain INVALID (2 references)
pkts bytes target prot opt in out source destination
19 844 INVDROP all -- * * 0.0.0.0/0 0.0.0.0/0 state INVALID
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x3F/0x00
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x3F/0x3F
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x03/0x03
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x06/0x06
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x05/0x05
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x11/0x01
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x18/0x08
0 0 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x30/0x20
9 360 INVDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:!0x17/0x02 state NEW
Chain INVDROP (10 references)
pkts bytes target prot opt in out source destination
28 1204 DROP all -- * * 0.0.0.0/0 0.0.0.0/0
Chain LOCALINPUT (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- !lo * 10.1.2.0/24 0.0.0.0/0
461 31652 ACCEPT all -- !lo * 78.129.132.155 0.0.0.0/0
6901 714K DSHIELD all -- !lo * 0.0.0.0/0 0.0.0.0/0
6831 695K SPAMHAUS all -- !lo * 0.0.0.0/0 0.0.0.0/0
Chain LOCALOUTPUT (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * !lo 0.0.0.0/0 10.1.2.0/24
600 32952 ACCEPT all -- * !lo 0.0.0.0/0 78.129.132.155
Chain LOGDROPIN (1 references)
pkts bytes target prot opt in out source destination
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:67
0 0 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:67
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:68
0 0 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:68
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:111
0 0 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:111
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:113
0 0 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:113
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpts:135:139
76 18810 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpts:135:139
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:445
0 0 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:445
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:500
0 0 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:500
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:513
0 0 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:513
0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:520
979 50908 DROP udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:520
26 1056 LOG tcp -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 30/min burst 5 LOG flags 0 level 4 prefix `Firewall: *TCP_IN Blocked* '
41 2173 LOG udp -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 30/min burst 5 LOG flags 0 level 4 prefix `Firewall: *UDP_IN Blocked* '
0 0 LOG icmp -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 30/min burst 5 LOG flags 0 level 4 prefix `Firewall: *ICMP_IN Blocked* '
72 3489 DROP all -- * * 0.0.0.0/0 0.0.0.0/0
Chain LOGDROPOUT (1 references)
pkts bytes target prot opt in out source destination
0 0 LOG tcp -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 30/min burst 5 LOG flags 0 level 4 prefix `Firewall: *TCP_OUT Blocked* '
0 0 LOG udp -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 30/min burst 5 LOG flags 0 level 4 prefix `Firewall: *UDP_OUT Blocked* '
0 0 LOG icmp -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 30/min burst 5 LOG flags 0 level 4 prefix `Firewall: *ICMP_OUT Blocked* '
3 183 DROP all -- * * 0.0.0.0/0 0.0.0.0/0
iptables -nvL -t nat
pez@brave:~$ sudo iptables -nvL -t nat
Chain PREROUTING (policy ACCEPT 42112 packets, 3106K bytes)
pkts bytes target prot opt in out source destination
Chain POSTROUTING (policy ACCEPT 716 packets, 43090 bytes)
pkts bytes target prot opt in out source destination
0 0 MASQUERADE all -- * * 192.168.122.0/24 !192.168.122.0/24
0 0 MASQUERADE all -- * venet0 10.10.0.0/24 0.0.0.0/0
31176 2345K MASQUERADE all -- * eth0 0.0.0.0/0 0.0.0.0/0
解决方案总结，在/etc/csf/中创建了新的文件csfpre，添加了以下内容：
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A INPUT -p gre -j ACCEPT
iptables -A OUTPUT -p gre -j ACCEPT
iptables -A FORWARD -i ppp+ -o eth0 -p ALL -j ACCEPT
iptables -A FORWARD -i eth0 -o ppp+ -p ALL -j ACCEPT
答案1
据我所知，您似乎没有启用 GRE 协议。您允许使用端口 47 TCP，但情况不一样。您rc.local关于 GRE 的规则似乎没问题，但可能已被覆盖，因此请在防火墙系统中添加这些规则。
您还具有用于转发数据包的 DROP 策略 - 至少添加此规则：
iptables -A FORWARD -i ppp+ -j ACCEPT
这将启用所有以 开头的接口的转发ppp，这对于基于 PPTP 的 VPN 来说已经足够了。
此外，您可能已经这样做了，但请检查您是否已启用数据包转发sysctl net.ipv4.ip_forward- 它应该是 1。
请注意，TCP 1723 的数据包数（第一列）为 0。尝试连接并检查它是否正常。但当然，请先启用 GRE，否则它将无法正常工作。