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How to configure FreeS/WAN
This page will teach you how to configure a simple network-to-network link or a Road Warrior connection between two Linux FreeS/WAN boxes.
See also these related documents:
our quickstart guide to opportunistic encryption
our guide to configuration with policy groups
our advanced configuration document
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 FreeS/WAN 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 with static IPs
a network behind each gate. Networks must have non-overlapping IP ranges.
Linux FreeS/WAN installed on both gateways
tcpdump on the local gate, to test the connection
For the Road Warrior you need:
one Linux box with a static IP
a Linux laptop with a dynamic IP
Linux FreeS/WAN installed on both
for testing, tcpdump on your gateway or laptop
If both IPs are dynamic, your situation is a bit trickier. Your best bet is a variation on the Road Warrior, as described in this mailing list message.
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 FreeS/WAN 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:
ssh2 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 gate, copy our template to /etc/ipsec.conf. (on Mandrake, /etc/freeswan/ipsec.conf). Substitute the information you've gathered for our example data.
conn net-to-net
left=192.0.2.2 # Local vitals
leftsubnet=192.0.2.128/29 #
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 FreeS/WAN 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:
scp2 ipsec.conf root@ab.example.com:/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 \! 192.0.2.128/29 -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 troubleshoot.
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 winstonnet-toledonet
To have the tunnel come up on-boot, replace
auto=add
with:
auto=start
Copy these changes to the other side, for example:
scp2 ipsec.conf root@ab.example.com:/etc/ipsec.conf
Enjoy!
Road Warrior Configuration
Gather information
You'll need to know:
the gateway's static IP
the IP range of the subnet behind that gateway
a name by which each side can identify itself for IPsec negotiations. Its form is a Fully Qualified Domain Name preceded by an @ sign, ie. @road.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 laptop, print your IPsec public key:
ipsec showhostkey --left
The output should look like this (with the key shortened for easy reading):
# RSA 2192 bits road.example.com Sun Jun 9 02:45:02 2002
leftrsasigkey=0sAQPIPN9uI...
Don't have a key? See these instructions.
...and your rightrsasigkey
Get a console on the gateway:
ssh2 xy.example.com
View the gateway's public key with:
ipsec showhostkey --right
This will yield something like
# RSA 2048 bits xy.example.com Fri Apr 26 15:01:41 2002
rightrsasigkey=0sAQOnwiBPt...
Customize /etc/ipsec.conf
On your laptop, copy this template to /etc/ipsec.conf. (on Mandrake, /etc/freeswan/ipsec.conf). Substitute the information you've gathered for our example data.
conn road
left=%defaultroute # Picks up our dynamic IP
leftnexthop=%defaultroute #
leftid=@road.example.com # Local information
leftrsasigkey=0sAQPIPN9uI... #
right=192.0.2.10 # Remote information
rightsubnet=10.0.0.0/24 #
rightid=@xy.example.com #
rightrsasigkey=0sAQOnwiBPt... #
auto=add # authorizes but doesn't start this
# connection at startup
The template for the gateway is different. Notice how it reverses left and right, in keeping with our convention that Left is Local, Right Remote. Be sure to switch your rsasigkeys in keeping with this.
ssh2 xy.example.com
vi /etc/ipsec.conf
and add:
conn road
left=192.0.2.2 # Gateway's information
leftid=@xy.example.com #
leftsubnet=192.0.2.128/29 #
leftrsasigkey=0sAQOnwiBPt... #
rightnexthop=%defaultroute # correct in many situations
right=%any # Wildcard: we don't know the laptop's IP
rightid=@road.example.com #
rightrsasigkey=0sAQPIPN9uI... #
auto=add # authorizes but doesn't start this
# connection at startup
Start your connection
You must start the connection from the Road Warrior side. On your laptop, type:
ipsec auto --start net-to-net
You should see:
104 "net-net" #223: STATE_MAIN_I1: initiate
106 "road" #301: STATE_MAIN_I2: sent MI2, expecting MR2
108 "road" #301: STATE_MAIN_I3: sent MI3, expecting MR3
004 "road" #301: STATE_MAIN_I4: ISAKMP SA established
112 "road" #302: STATE_QUICK_I1: initiate
004 "road" #302: STATE_QUICK_I2: sent QI2, IPsec SA established
Look for 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 \! 192.0.2.128/29 -j MASQUERADE
Test your connection
From your laptop, ping a subnet node behind the remote gateway. Do not choose the gateway itself for this test.
ping ns.winston.example.com
Snoop the packets exiting the laptop, with a command like:
tcpdump -i wlan0
You have success if you see (Encapsulating Security Payload) packets travelling in both directions:
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 do, great! Traffic between your Road Warrior and the net behind your gateway is protected. If not, see our troubleshooting hints.
Your new tunnel protects only traffic addressed to the net, not to the IPsec gateway itself. If you need the latter, you'll want to make an extra tunnel..
Finishing touches
On both ends, name your connection wisely, like:
conn mike-to-office
On the laptop only, replace
auto=add
with:
auto=start
so that you'll be connected on-boot.
Happy telecommuting!
Multiple Road Warriors
If you're using RSA keys, as we did in this example, you can add as many Road Warriors as you like. The left/rightid parameter lets Linux FreeS/WAN distinguish between multiple Road Warrior peers, each with its own public key.
The situation is different for shared secrets (PSK). During a PSK negotiation, ID information is not available at the time Pluto is trying to determine which secret to use, so, effectively, you can only define one Roadwarrior connection. All your PSK road warriors must therefore share one secret.