How to configure Openswan - Openswan to Openswan connections (using RSASIG or PSK)

• The network-to-network setup allows you to connect two office networks into one Virtual Private Network, while the Road Warrior connection secures a laptop’s telecommute to work. Our examples also show the basic procedure on the Linux Openswan side where another IPsec peer is in play.Shortcut to net-to-net.Shortcut to Road Warrior.

Requirements

To configure the network-to-network connection you must have:

• two Linux gateways
• Openswan installed on both gateways
• a network behind each gateway. Networks must have non-overlapping IP ranges.

For the Road Warrior you need:

• one Linux box with a static IP
• a Linux laptop with a dynamic IP
• Openswan installed on both
• tcpdump (optional) on the local gateway, to test the connection

If both IPs are dynamic, your situation is a bit trickier. Your best bet is a variation on the RoadWarrior.

Net-to-Net connection

Gather information

For each gateway, compile the following information:

• gateway IP
• IP range of the subnet you will be protecting. This doesn’t have to be your whole physical subnet.
• a name by which that gateway can identify itself for IPsec negotiations. Its form is a Fully Qualified Domain Name preceded by an @ sign, ie. @xy.example.com.It does not need to be within a domain that you own. It can be a made-up name.

Get your leftrsasigkey

On your local Linux Openswan gateway, print your IPsec public key:

# ipsec showhostkey --left

The output should look like this (with the key shortened for easy reading):

    # RSA 2048 bits   xy.example.com   Fri Apr 26 15:01:41 2002
    leftrsasigkey=0sAQOnwiBPt...

Don’t have a key? Use ipsec newhostkey to create one.

…and your rightrsasigkey

Get a console on the remote side:

# ssh ab.example.com

In that window, type:

# ipsec showhostkey --right

You’ll see something like:

    # RSA 2192 bits   ab.example.com   Thu May 16 15:26:20 2002
    rightrsasigkey=0sAQOqH55O...

Edit /etc/ipsec.conf

Back on the local gateway, copy our template to /etc/ipsec.conf. (on Mandrake, /etc/openswan/ipsec.conf). Substitute the information you’ve gathered for our example data.

conn net-to-net
    left=192.0.2.2                 # Local vitals
    leftsubnet=172.16.0.0/24       #
    leftid=@xy.example.com         #
    leftrsasigkey=0s1LgR7/oUM...   #
    leftnexthop=%defaultroute      # correct in many situations
    right=192.0.2.9                # Remote vitals
    rightsubnet=10.0.0.0/24        #
    rightid=@ab.example.com        #
    rightrsasigkey=0sAQOqH55O...   #
    rightnexthop=%defaultroute     # correct in many situations
    auto=add                       # authorizes but doesn't start this
                                   # connection at startup

 "Left" and "right" should represent the machines that have Openswan installed on them, and "leftsubnet" and "rightsubnet" machines that are being protected. /32 is assumed for left/right and left/rightsubnet parameters.

Copy conn net-to-net to the remote-side /etc/ipsec.conf. If you’ve made no other modifications to either ipsec.conf, simply:

# scp ipsec.conf 
 This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
 :/etc/ipsec.conf

Start your connection

Locally, type:

# ipsec auto --up net-to-net

You should see:

    104 "net-net" #223: STATE_MAIN_I1: initiate
    106 "net-net" #223: STATE_MAIN_I2: sent MI2, expecting MR2
    108 "net-net" #223: STATE_MAIN_I3: sent MI3, expecting MR3
    004 "net-net" #223: STATE_MAIN_I4: ISAKMP SA established
    112 "net-net" #224: STATE_QUICK_I1: initiate
    004 "net-net" #224: STATE_QUICK_I2: sent QI2, IPsec SA established

The important thing is IPsec SA established. If you’re unsuccessful, see our troubleshooting tips.

Do not MASQ or NAT packets to be tunneled

If you are using IP masquerade or Network Address Translation (NAT) on either gateway, you must now exempt the packets you wish to tunnel from this treatment. For example, if you have a rule like:

# iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/24 -j MASQUERADE

change it to something like:

# iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/24 -d ! 172.16.0.0/24 -j MASQUERADE

This may be necessary on both gateways.

Test your connection

Sit at one of your local subnet nodes *(not the gateway)*, and ping a subnet node on the other *(again, not the gateway)*.

$ ping fileserver.toledo.example.com

While still pinging, go to the local gateway and snoop your outgoing interface, for example:

# tcpdump -i ppp0

You want to see ESP (Encapsulating Security Payload) packets moving back and forth between the two gateways at the same frequency as your pings:

    19:16:32.046220 192.0.2.2 > 192.0.2.9: ESP(spi=0x3be6c4dc,seq=0x3)
    19:16:32.085630 192.0.2.9 > 192.0.2.2: ESP(spi=0x5fdd1cf8,seq=0x6)

If you see this, congratulations are in order! You have a tunnel which will protect any IP data from one subnet to the other, as it passes between the two gates. If not, go and see our Troubleshooting page.

Note: your new tunnel protects only net-net traffic, not gateway-gateway, or gateway-subnet. If you need this (for example, if machines on one net need to securely contact a fileserver on the IPsec gateway), you’ll need to create extra connections.

Finishing touches

Now that your connection works, name it something sensible, like:

conn newyork-net-to-washington-net

To have the tunnel come up on-boot, replace

    auto=add

with:

    auto=start

Copy these changes to the other side, for example:

# scp ipsec.conf 
 This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
 :/etc/ipsec.conf

Enjoy!

______________________________________________________________________________

Thanks to http://techgurulive.com/2008/11/12/how-to-configure-openswan-openswan-to-openswan-connections-using-rsasig-or-psk/