VPN Client
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Now we examine the client end. In practice, when used to allow access to a remote network, this box can easily serve as a Samba (Windows Networking) server, DHCP server, and even an internal web server. The important thing to remember is that this box should be as secure as possible, as it runs your whole remote network. |
The Kernel
First things first, you must have ppp available in your kernel. If you are going to allow multiple machines to use the tunnel, then you need to have firewalling and forwarding available too. If the client is going to be a single machine, ppp is enough.
Bring up the link
The link is created by running pppd through a pseudo terminal that is created by pty-redir and connected to ssh. This is done with something similar to the following sequence of commands:
# /usr/sbin/pty-redir /usr/bin/ssh -t -e none -o 'Batchmode yes' \ -c blowfish -i /root/.ssh/identity.vpn -l joe > /tmp/vpn-device # sleep 10 # /usr/sbin/pppd `cat /tmp/vpn-device` # sleep 15 # /sbin/route add -net 172.16.0.0 gw vpn-internal.mycompany.com netmask 255.240.0.0 # /sbin/route add -net 192.168.0.0 gw vpn-internal.mycompany.com netmask 255.255.0.0 |
What this does is run ssh, redirecting the input and output to pppd. The options passed to ssh configure it to run without escape characters (-e), using the blowfish crypto algorithm (-c), using the identity file specified (-i), in terminal mode (-t), with the options 'Batchmode yes' (-o). The sleep commands are used to space out the executions of the commands so that each can complete their startup before the next is run.
LRP - Linux Router Project
I actually run this setup on Pentium 90's running the LRP distribution of Linux. LRP is a distribution of Linux that fits in, and boots off of a single floppy disk. You can learn more about it at http://www.linuxrouter.org/ You can download my LRP package for the VPN client from here. You will also need both the ppp and ssh packages from the LRP site.