The FreeBSD Diary

Thank you Philip.

A VPN (virtual LAN) allows you to treat two physically separate networks as though they were on the same network. At least that's how I understand it. What's cool about this is that it allows my home network and my office network to appear to be one contiguous network allowing me to work from one or the other without a lot of differences.

I'm going to use the following fictitious networks to illustrate my steps. Below we have two separate networks whose gateways (or routers, or firewall/natd boxes ,etc.) are gw1 and gw2. Our goal is to make it appear to the machines on either LAN that it is one seamless network. Additionally we want any data that is transferred between the two networks to be secure (encrypted). We do that by setting up a secure tunnel.

(Note: In my case, gw1 is 3.4 and gw2 is 4.0. I believe there are other ways to do this using an all 4.0 solution, but that doesn' work for me)

        ___________                                     ___________
        |         |                                     |         |
10.0.0.1-   gw1   -111.111.111.111 <---> 222.222.222.222-   gw2   -10.1.0.1
  (LAN) |         |   (Internet)           (Internet)   |         |  (LAN)
        |_________|                                     |_________| 
             |                                               | 
          10.2.0.1 <------------ encrypted> 10.2.0.2
          (tunnel)                                        (tunnel)

Steps:

1. Make sure that you have at least one tunnel device compiled into the kernel on both gw1 and gw2. In particular you want to make sure your kernel config has the following:

   pseudo-device tun 1

   If you're going to have multiple vlans (perhaps the office server will provide vlans for multiple employee's home networks) then you should increase 1 to something larger. Build the new kernel, install it, and make the devices.

2. Install the pipsecd port on both machines. FreeBSD-3.4 will also install OpenSSL, 4.0 won't since it's already there. Nothing special needs to be done besides a "make install".
3. On gw1 create /usr/local/etc/rc.d/pipsecd.sh with the following:

   #!/bin/sh
   
   /usr/local/sbin/pipsecd &#
   # For some reason 4.0 complains if we access the tun device
   # to soon after calling pipsecd.  Sleeping for a bit fixes that.
   #
   sleep 3
   /sbin/ifconfig tun0 10.2.0.2 10.2.0.1 netmask 255.255.255.0
   /sbin/route add -net 10.1.0.0 -netmask 255.255.255.0 10.2.0.1
   

4. On gw2 create /usr/local/etc/rc.d/pipsecd.sh with the following:

   #!/bin/sh
   
   /usr/local/sbin/pipsecd &#
   # For some reason 4.0 complains if we access the tun device
   # to soon after calling pipsecd.  Sleeping for a bit fixes that.
   #
   sleep 3
   /sbin/ifconfig tun0 10.2.0.1 10.2.0.2 netmask 255.255.255.0
   /sbin/route add -net 10.0.0.0 -netmask 255.255.255.0 10.2.0.2
   

5. On gw1 create /usr/local/etc/ipsec/pipsecd.conf with the following. 'XXXXX', 'YYYYY', 'AAAAA', 'BBBBB' can be changed to any string of characters (as far as I can tell) as long as you change them in both files (these lines have been split for readability; there is actually only three lines in this file).

   sa ipesp spi=1000 auth=hmac-md5-96 akey=XXXXX enc=blowfish_cbc 
                                         ekey=AAAAA dest=222.222.222.222
   sa ipesp spi=1000 auth=hmac-md5-96 akey=YYYYY enc=blowfish_cbc 
                                         ekey=BBBBB
   if /dev/tun0 local_spi=1000 remote_spi=1000

6. On gw2 create /usr/local/etc/ipsec/pipsecd.conf with the following (these lines have been split for readability; there is actually only three lines in this file):

   sa ipesp spi=1000 auth=hmac-md5-96 akey=XXXXX enc=blowfish_cbc 
                                    ekey=AAAAA
   sa ipesp spi=1000 auth=hmac-md5-96 akey=YYYYY enc=blowfish_cbc 
                                    ekey=BBBBB dest=111.111.111.111
   if /dev/tun0 local_spi=1000 remote_spi=1000

7. That's it. Now, on both machines, start pipsecd by typing (as root):

   sh /usr/local/etc/rc.d/pipsecd.sh

At this point machines on either LAN should be able to connect to machines on the other LAN -- that is, host 10.0.0.2 should be able to ping 10.1.0.2 provided that they are both on.

For some reason the gateways themselves will not be able to talk to each other. When I setup my first VPN they could, but I must have changed something by accident and now they can't. But it's not that big of a deal because you shouldn't be connecting from/to your gateways very much anyway.

Notes:

• If there are firewalls involved you will need to add some rules. The following example is for IPFW running on gw1, whose external interface is 'ed0':

  add 8000 allow 50 from 222.222.222.222 to 111.111.111.111 in recv ed0
  add 8000 allow ip from any to any via tun0

• My specific hardware:
  • Office - FreeBSD 3.4, P120, 64RAM, 512K DSL connection
  • Home 1 - FreeBSD 3.4, P133, 32RAM, 512K DSL connection
  • Home 2 - FreeBSD 4.0, P120, 64RAM, 512K DSL connection

I max out the 512K DSL connection easily transferring b/n these servers (encryption and all). "Home 1" also runs Apache, Samba, netatalk, mysql, DNS, SMTP, POP, firewall, natd, and dhcp without problems.

In other words, you *don't* need beefy hardware.