This page will get you started using Linux FreeS/WAN with opportunistic encryption (OE). OE enables you to set up IPsec tunnels without co-ordinating with another site administrator, and without hand configuring each tunnel. If enough sites support OE, a "FAX effect" occurs, and many of us can communicate without eavesdroppers.
Please see this list of known issues with Opportunistic Encryption.
To set up opportunistic encryption, you will need:
Note: Currently, only Linux FreeS/WAN supports opportunistic encryption.
Our instructions are for a recent Red Hat with a stock Red Hat kernel. For other ways to install, see our install document.
Check your kernel version with
uname -a
From our FTP site, get the kernel module which matches your kernel. For example:
freeswan-module-2.00_2.4.18_3-0.i386.rpm
Note: Our kernel modules will only work on the Red Hat kernel they were built for, since they are very sensitive to small changes in the kernel.
Get FreeS/WAN utilities to match. For example:
freeswan-userland-2.00_2.4.18_3-0.i386.rpm
While you are there, grab the RPM signing key
freeswan-rpmsign.asc
If you're running RedHat 8.x, import this key into the RPM database:
rpm --import freeswan-rpmsign.asc
For RedHat 7.x systems, you'll need to add it to your PGP keyring:
pgp -ka freeswan-rpmsign.asc
Check the signatures on both RPMs using:
rpm --checksig freeswan*.rpm
You should see output like:
freeswan-module-2.00_2.4.18_3-0.i386.rpm: pgp md5 OK
freeswan-userland-2.00_2.4.18_3-0.i386.rpm: pgp md5 OK
Become root:
su
Install your RPMs with:
rpm -ivh freeswan*.rpm
If you've installed FreeS/WAN RPMS before, see our note on upgrading from 1.x to 2.x RPMs.
Then, start FreeS/WAN:
service ipsec start
To check that you have a successful install, run:
ipsec verify
You should see at least:
Checking your system to see if IPsec got installed and started correctly
Version check and ipsec on-path [OK]
Checking for KLIPS support in kernel [OK]
Checking for RSA private key (/etc/ipsec.secrets) [OK]
Checking that pluto is running [OK]
If any of these first four checks fails, see our troubleshooting guide.
Determine the best form of opportunism your system can support.
When you set up initiate-only Opportunistic Encryption (iOE):
You cannot network a group of initiator-only machines if none of these is capable of responding to OE. If one is capable of responding, you may be able to create a hub topology using routing.
Find a DNS forward domain (e.g. example.com) where you can publish your key. You'll need access to the DNS zone files for that domain. This is common for a domain you own. Some free DNS providers, such as this one, also provide this service.
Dynamic IP users take note: the domain where you place your key need not be associated with the IP address for your system, or even with your system's usual hostname.
Choose a name within that domain which you will use to identify your machine. Normally, but not always, your ID is the same as your machine name. Our machine is called xy, and we'll choose the corresponding FQDN xy.example.com.
Generate a DNS KEY record containing your system's public key with the command:
ipsec showhostkey
This command takes the contents of /etc/ipsec.secrets and reformats it into something usable by ISC's BIND. The result should look like this (with the key data trimmed down for clarity):
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000
xy.example.com. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
Change xy.example.com to your FQDN.
Insert the record into DNS, or have a system adminstrator do it for you. It may take up to 48 hours for the record to propagate, but it's usually much quicker.
Check your DNS work
ipsec verify --host xy.example.com
You ought to see something like:
Looking for forward key for xy.example.com [OK]
For this type of opportunism, only the forward key test is relevant.
Place this iOE connection in /etc/ipsec.conf. It's a copy of a built in OE connection, modified to use a custom ID:
conn iprivate-or-clear
leftid=@xy.example.com # put your ID here
also=private-or-clear
Use your own FQDN ID, preceded by an @sign, instead of @xy.example.com.
Create a group file for this connection in /etc/ipsec.d/policies . An OE connection will be instantiated for hosts within the CIDR blocks listed in its group file.
cp -p /etc/ipsec.d/policies/private-or-clear /etc/ipsec.d/policies/iprivate-or-clear
Make iprivate-or-clear your default policy by placing fullnet in its group file:
[root@xy root]# cat /etc/ipsec.d/policies/iprivate-or-clear
# This file defines the set of CIDRs (network/mask-length) to which
# communication should be private, if possible, but in the clear otherwise.
....
0.0.0.0/0
Restart FreeS/WAN so the changes take effect:
service ipsec restart
You can create more complex iOE configurations as explained in our policy groups document, or disable OE using these instructions.
That's it! Test your connection.
Full opportunism allows you to initiate and receive opportunistic connections on your machine.
You must be able to publish these directly in the reverse domain. FreeS/WAN will not follow a PTR which appears in the reverse, since a second lookup at connection start time is too costly.
Generate a KEY record:
ipsec showhostkey
This command takes the contents of /etc/ipsec.secrets and reformats it into something usable by ISC's BIND. It will yield (with key data trimmed for clarity):
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000 xy.example.com IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
Edit it to insert the IP address in reverse map format. For example, 192.0.2.11 becomes 11.2.0.192.in-addr.arpa.. Note the final period. The result:
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000 11.2.0.192.in-addr.arpa. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
This record lets others know that this machine can receive opportunistic connections. It also lets them know that the machine is authorized to encrypt on its own behalf.
Use the command:
ipsec showhostkey --txt 192.0.2.11
where you replace 192.0.2.11 with your public IP.
The record (with key shortened) looks like:
; RSA 2048 bits xy.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
Send these records to your ISP, to be published in your IP's reverse map. It may take up to 48 hours for these to propagate, but usually takes much less time.
Check your DNS work with
ipsec verify --host xy.example.com
You ought to see something like:
Looking for TXT in reverse map: 11.2.0.192.in-addr.arpa [OK]
Looking for KEY in reverse map: 11.2.0.192.in-addr.arpa [OK]
which indicates that you've passed both reverse-map tests.
FreeS/WAN 2.x ships with full OE enabled, so you don't need to configure anything. To enable OE out of the box, FreeS/WAN 2.x uses the policy group private-or-clear, which creates IPsec connections if possible (using OE if needed), and allows traffic in the clear otherwise. You can create more complex OE configurations as described in our policy groups document, or disable OE using these instructions.
If you've previously configured for initiator-only opportunism, remove leftid= from config setup, so that peer FreeS/WANs will look up your key by IP. Restart FreeS/WAN so that your change will take effect, with
service ipsec restart
If you are running a default install of RedHat 8.x, take note: you will need to alter your iptables rule setup to allow IPSec traffic through your firewall. See our firewall document for sample iptables rules.
That's it. Now, test your connection.
Full opportunism allows you to initiate and receive opportunistic connections on your machine. The remaining instructions in this section assume you have first set up full opportunism on your gateway using these instructions. Both sets of instructions require mailing DNS records to your ISP. Collect DNS records for both the gateway (above) and the subnet nodes (below) before contacting your ISP.
You need these so that your Opportunistic peers can:
On the gateway, generate a TXT record with:
ipsec showhostkey --txt 192.0.2.11
Use your gateway address in place of 192.0.2.11.
You should see (keys are trimmed for clarity throughout our example):
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
This MUST BE the same key as in your gateway's KEY record, or nothing will work.
In a text file, make one copy of this TXT record for each subnet node:
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
Above each entry, insert a line like this:
98.2.0.192.in-addr.arpa. IN PTR arthur.example.com.
It must include:
The result will be a file of TXT records, like this:
98.2.0.192.in-addr.arpa. IN PTR arthur.example.com
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
99.2.0.192.in-addr.arpa. IN PTR ford.example.com.
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
100.2.0.192.in-addr.arpa. IN PTR trillian.example.com.
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000
IN TXT "X-IPsec-Server(10)=192.0.2.11" " AQOF8tZ2...+buFuFn/"
Ask your ISP to publish all the reverse DNS records you have collected. There may be a delay of up to 48 hours as the records propagate.
Check a couple of records with commands like this one:
ipsec verify --host ford.example.com
ipsec verify --host trillian.example.com
You should see:
....
Looking for TXT in reverse map: 99.2.0.192.in-addr.arpa [OK]
....
Looking for TXT in reverse map: 100.2.0.192.in-addr.arpa [OK]
FreeS/WAN 2.x ships with a built-in, automatically enabled OE connection conn packetdefault which applies OE, if possible, to all outbound traffic routed through the FreeS/WAN box. The ipsec.conf(5) manual describes this connection in detail. While the effect is much the same as private-or-clear, the implementation is different: notably, it does not use policy groups.
You can create more complex OE configurations for traffic forwarded through a FreeS/WAN box, as explained in our policy groups document, or disable OE using these instructions.
Instructions are in the next section.
Be sure IPsec is running. You can see whether it is with:
ipsec setup status
If need be, you can restart it with:
service ipsec restart
Load a FreeS/WAN test website from the host on which you're running FreeS/WAN. Note: the feds may be watching these sites. Type one of:
links oetest.freeswan.org
links oetest.freeswan.nl
A positive result looks like this:
You seem to be connecting from: 192.0.2.11 which DNS says is:
gateway.example.com
_________________________________________________________________
Status E-route
OE enabled 16 192.139.46.73/32 -> 192.0.2.11/32 =>
tun0x2097@192.0.2.11
OE enabled 176 192.139.46.77/32 -> 192.0.2.11/32 =>
tun0x208a@192.0.2.11
If you see this, congratulations! Your OE host or gateway will now encrypt its own traffic whenever it can. If you have difficulty, see our OE troubleshooting tips.
If you've set up FreeS/WAN to protect a subnet behind your gateway, you'll need to run another simple test, which can be done from a machine running any OS. That's right, your Windows box can be protected by opportunistic encryption without any FreeS/WAN install or configuration on that box. From each protected subnet node , load the FreeS/WAN website with:
links oetest.freeswan.org
links oetest.freeswan.nl
A positive result looks like this:
You seem to be connecting from: 192.0.2.98 which DNS says is:
box98.example.com
_________________________________________________________________
Status E-route
OE enabled 16 192.139.46.73/32 -> 192.0.2.98/32 =>
tun0x134ed@192.0.2.11
OE enabled 176 192.139.46.77/32 -> 192.0.2.11/32 =>
tun0x134d2@192.0.2.11
If you see this, congratulations! Your OE gateway will now encrypt traffic for this subnet node whenever it can. If you have difficulty, see our OE troubleshooting tips.
When testing OE, you will often find it useful to execute this command on the FreeS/WAN host:
ipsec eroute
If you have established a connection (either for or for a subnet node) you will see a result like:
192.0.2.11/32 -> 192.139.46.73/32 => tun0x149f@192.139.46.38
Key:
| 1. | 192.0.2.11/32 | Local start point of the protected traffic. |
| 2. | 192.0.2.194/32 | Remote end point of the protected traffic. |
| 3. | 192.0.48.38 | Remote FreeS/WAN node (gateway or host). May be the same as (2). |
| 4. | [not shown] | Local FreeS/WAN node (gateway or host), where you've produced the output. May be the same as (1). |
For extra assurance, you may wish to use a packet sniffer such as tcpdump to verify that packets are being encrypted. You should see output that indicates ESP encrypted data, for example:
02:17:47.353750 PPPoE [ses 0x1e12] IP 154: xy.example.com > oetest.freeswan.org: ESP(spi=0x87150d16,seq=0x55)
Please see our policy groups document for more ways to set up Opportunistic Encryption.
You may also wish to make some pre-configured connections.
This table is a work in progress. We welcome contributions via the users' mailing list.
| Symptom | Problem | Action |
| OE host is very slow to contact other hosts. | Slow DNS service while running OE. | It's a good idea to run a caching DNS
server on your OE host, as outlined in
this mailing list message. If your DNS servers are elsewhere, put
their IPs in the clear policy group, and re-read groups with
ipsec auto --rereadgroups |
Can't Opportunistically initiate for 192.0.2.2 to 192.0.2.3: no TXT record for 13.2.0.192.in-addr.arpa. | Peer is not set up for OE. |
None. Plenty of hosts on the Internet do not run OE. If, however, you have set OE up on that peer, this may indicate that you need to wait up to 48 hours for its DNS records to propagate. |
ipsec verify does not find DNS records:
Looking for forward key... [FAILED] Looking for KEY in reverse map...[FAILED]You also experience authentication failure: Possible authentication failure: no acceptable response to our first encrypted message | DNS records are not posted or have not propagated. | Did you post the DNS records necessary for OE? If not, do so using the instructions in our quickstart guide. If so, wait up to 48 hours for the DNS records to propagate. |
| ipsec verify does not find DNS records, and you experience authentication failure. | For iOE, leftid does not match location of forward DNS record. | In your iOE connections, change leftid= to match the forward DNS where you posted the record. For reference, see our iOE instructions. |
| ipsec verify finds DNS records, yet there is still authentication failure. ( ? ) | DNS records are malformed. | Re-create the records and send new copies to your DNS administrator. |
| ipsec verify finds DNS records, yet there is still authentication failure. ( ? ) | DNS records show different keys for a gateway vs. its subnet hosts. | All KEY records for boxes protected by an OE gateway must contain the gateway's public key. Re-create and re-post any incorrect records using these instructions. |
| OE gateway loses connectivity to its subnet. The gateway's routing table shows routes to the subnet through IPsec interfaces. | The subnet is part of the private or block policy group on the gateway. | Remove the subnet from the group, and
reread groups with
ipsec auto --rereadgroups |
| OE does not work to hosts on the local LAN. | This is a known issue. | See this list of known issues with OE. |