问通过ssh设置隧道并为VPN客户端使用它的Internet

EN

man ssh

SSH-BASED VIRTUAL PRIVATE NETWORKS
 ssh contains support for Virtual Private Network (VPN) tunnelling using the tun(4) network pseudo-device, allowing two networks to be joined securely.  The sshd_config(5) configuration option PermitTunnel controls whether the server sup-
 ports this, and at what level (layer 2 or 3 traffic).

 The following example would connect client network 10.0.50.0/24 with remote network 10.0.99.0/24 using a point-to-point connection from 10.1.1.1 to 10.1.1.2, provided that the SSH server running on the gateway to the remote network, at
 192.168.1.15, allows it.

 On the client:

       # ssh -f -w 0:1 192.168.1.15 true
       # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
       # route add 10.0.99.0/24 10.1.1.2

 On the server:

       # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
       # route add 10.0.50.0/24 10.1.1.1

 Client access may be more finely tuned via the /root/.ssh/authorized_keys file (see below) and the PermitRootLogin server option.  The following entry would permit connections on tun(4) device 1 from user ``jane'' and on tun device 2 from
 user ``john'', if PermitRootLogin is set to ``forced-commands-only'':

   tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
   tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john

 Since an SSH-based setup entails a fair amount of overhead, it may be more suited to temporary setups, such as for wireless VPNs.  More permanent VPNs are better provided by tools such as ipsecctl(8) and isakmpd(8).