This file is part of the documentation for the Linux FreeS/WAN project.
See the documentation index or project home page for more information.

Linux FreeS/WAN Setup

This document describes setting up a VPN (Virtual Private Network) using Linux FreeS/WAN (Secure Wide Area Network). Other documents in the distribution cover: Kurt Seifried has written two documents describing how to set up FreeS/WAN: This document is intended to provide everything you will require, but have a look at his as well.

Setting up a secure tunnel to create a VPN

The problem we are trying to solve is that of letting two networks communicate securely when the only connection between them is over a third network which they do not trust.

The solution is to put a security gateway machine between each of the communicating networks and the untrusted network. The gateway machines encrypt packets entering the untrusted net and decrypt packets leaving it, creating a secure tunnel through it.

The result is called a VPN, a Virtual Private Network. If the cryptography is strong, the implementation careful, and the administration of the gateways competent, then one can reasonably place considerable confidence in the security of the tunnel. The two networks then behave like a large private network, some of whose links are encrypted tunnels through untrusted nets.

Actual VPNs are often more complex. One organisation may have fifty branch offices, plus some suppliers and clients, with whom it needs to communicate securely. Another might have 5,000 stores, or 50,000 point-of-sale devices. Many VPNs need to handle travelling users, the "road warrior" connecting to home base from a laptop machine.

The untrusted network need not be the Internet. All the same issues arise on a corporate or institutional network whenever two departments want to communicate privately with each other.

Our example network

For our example, we assume that there are only three networks involved, two that want to talk to each other plus the Internet in the role of the third, untrusted, net. Once you have this working between two network gateways, extending it to three or more is straightforward.

We also assume here that all machines involved have known, fixed IP addresses. See our Configuration document for some information on supporting "road warriors".

In our example, we'll call the two gateways East and West. We'll have only one client machine on each net: Sunrise in the East and Sunset in the West.

A diagram:

              local net       untrusted net       local net

Our goal in this document is to tell you how to set up the two gateways, East and West. We assume your goal is to ensure that East and West encrypt all traffic between them, or at least all that your security policies require them to encrypt.

SuSE 6.3

The European version of the SuSE 6.3 distribution ships with FreeS/WAN included. If you are using that, you need not download kernel source and FreeS/WAN code, then apply our kernel patches and install the rest of FreeS/WAN. That should all be done for you already. All you have to do is:

Here, users of that SuSE release can skip ahead to our section on editing configuration files.

Installation steps

    Before starting the install

  1. Configure, compile, install, test and back up Linux kernels on both gateways, without FreeS/WAN.

    Choosing a kernel

    Development work and testing are currently done on Intel architecture machines using:
    • Red Hat 5.2 distribution and kernel version 2.0.38
    • Red Hat 6.0 distribution and kernel version 2.2.12

    If you are going to use any 2.0.x kernel, we strongly recommend 2.0.38 (or a later version if one appears). 2.0.38 has fixes for a number of small security-related glitches; nothing major, but definitely worth having on a security gateway machine. Also, some things we were patching in 2.0.36 are built into 2.0.38 kernels. Our patch set should still work on earlier kernels, but this is not something we test often.

    For 2.2 kernels, we suggest using either 2.2.12 to match our development systems, or the latest kernel release. Our code is intended to work on any 2.2 kernel.

    Our code includes patches, mostly user-contributed, to make it work on 2.3 kernels. (In the Linux release numbering system, an even second digit as in 2.2.x indicates a stable or production release while an odd number as in 2.3.x indicates an experimental or development release). The patches have been tested successfully on 2.3 kernels up to 2.3.20-something, but are not regularly or intensively tested by our team. If you are working with 2.3.x, we suggest you use our latest snapshot rather than our release to be sure of getting the latest patches.

    For information on other CPU architectures see our Implementation Notes file and our Compatibility document.

    Getting kernel source

    There are many sources on the net for Linux kernels. All the major distribution vendors provide them. See for example: For kernels direct from Linus, without any distribution vendor's modifications, see the mirror list, or go directly to ftp.<your country>, with the appropriate two-letter country code inserted.

    The International kernel patches add cryptographic code that cannot be in the vanilla kernel because that is distributed from the US and must comply with American export laws. These patches are not required for FreeS/WAN; we add our own cryptographic code.

    For any of these, choose a mirror that is close to you and bookmark it.

    Using a kernel from your distribution vendor may save you some annoyance later.

    • Different distributions put the kernel in different places (/vmlinuz, /boot/vmlinuz, /boot/vmlinuz-2.2.15 ...) and set lilo (the Linux loader) up differently. With a kernel from your distribution vendor, everything works right. With other combinations, a newly compiled kernel may be installed in one place while lilo is looking in another. You can of course adjust the kernel Makefile and/or /etc/lilo.conf to solve this problem, but we suggest just avoiding it.
    • Also, distributions vendors may include patches or drivers which are not part of the standard kernel. If you install a standard kernel, you must either do without those features or download then patches and add them yourself.
    Kernel source normally resides in /usr/src/linux, whether you from the distribution CD or download a tar file into /usr/src and untar it there.

    We suggest the same procedure for FreeS/WAN. Put the tarfile under /usr/src. You will get a directory /usr/src/freeswan<version> when you untar.

    Note that these methods don't work:

    • putting freeswan under /usr/src/linux; the links become confused
    • untarring in one place, then cp -R to move it where you want it; some necessary symbolic links are not copied

    Kernel configuration

    You need to configure the gateway kernels because some of our utilities rely on the results of configuration.

    You should compile, install and test the kernels as you have configured them, so that you have a known stable starting point. Then if there is a problem after you add FreeS/WAN, tracking it down is much simpler.

    If you need advice on this process, or general Linux background information, try our list of Linux web references. The most directly relevant document is the Kernel HOWTO. We also provide a file of notes on kernel installation.

  2. Configure and test IP networking on both gateways and on at least one client machine behind each of them. If you need advice on this, your best sources are likely the Net-3 Networking Howto and the Network Administrator's Guide.

    The client machines, Sunrise and Sunset in our example, may have assigned routable IP addresses, or they may be using private non-routable addresses (as defined in RFC 1918) with the gateways doing IP masquerade. It doesn't matter which, as long as whatever it is works correctly.

    • If Sunrise and Sunset have routable IP addresses, test that they can ping each other.
    • If IP masquerading is in use, test as far as you can. For example, if Sunset is masqueraded behind West then Sunrise cannot ping Sunset but should be able to ping West. Whether Sunset can ping Sunrise, assuming Sunrise is not masqueraded, would depend on whether West's rules let ICMP packets through. If not, you should adjust those rules.
    In any case, it is not enough to just test that East and West can communicate.

    Configure and test any other software you will want to use for testing once IPSEC is up. For example, you might put an HTTP daemon on Sunset and a browser on Sunrise. Make sure these work without IPSEC.

    If these tests fail, figure out why and fix it.
    Do not proceed until it works.

    Building the software

  3. Did you do the steps listed above? If not, go back and do them now.

  4. Build and install FreeS/WAN per the INSTALL file (found in the top level directory of the distribution) on both gateways.

    This installs various programs, man pages, and configuration files. It also adds FreeS/WAN code to the kernel, then re-compiles and re-configures the kernel to activate that code.

    When you get to the step using config menuconfig or xconfig to check configuration after adding the FreeS/WAN patches to your kernel:

    • Unless you have very specific needs for it, accept the default and leave PK-key disabled. This is experimental code, not yet ready for prime time.
    • Save the new configuration even if you make no changes. This ensures that the FreeS/WAN changes are actually seen by the system.

    The ipsec.conf(5) configuration file

  5. Pick one machine on which you will edit the two files:

    • /etc/ipsec.conf -- configuration of ipsec connections
    • /etc/ipsec.secrets -- secrets shared with other machines

    Note that these edits must be done securely if you are to have any confidence in your IPSEC security. If someone can get the contents of these files, for example by looking at your screen as you work or by intercepting packets between your X desktop and the gateway machine, then they can easily bypass IPSEC. You need to edit these two files to configure at least one IPSEC connection.

    As with most things on any Unix-like system, most parts of Linux FreeS/WAN are documented in online manual pages. We provide a list of FreeS/WAN man pages, with links to HTML versions of them. The /etc/ipsec.conf file is documented in the ipsec.conf(5) man page. You should now read that page, either via this link or with the command:

    	man 5 ipsec.conf
    You may also want to look at manual pages for ipsec_manual(8) and ipsec_auto(8) which document the two types of connections you will set up here, and at our example configurations file.

    We currently support two types of connections, started with commands such as:

    	ipsec manual --start name
    	ipsec auto --up name
    The difference is in how they are keyed.
    Manually keyed connections
    use keys stored in /etc/ipsec.conf.
    Automatically keyed connections
    use keys automatically generated by the Pluto key negotiation daemon. The key negotiation protocol, IKE, authenticates the other system using shared secrets stored in /etc/ipsec.secrets.

    Here we will set up a connection for both manual mode (useful for testing) and automatic mode (more secure, used in production). The steps involved are:

    • edit connection information used by both modes, in /etc/ipsec.conf
    • add keys for manual mode, in /etc/ipsec.conf
    • add secrets used for authentication during key negotiation, in /etc/ipsec.secrets

    The setup section of /etc/ipsec.conf

    The first section of ipsec.conf contains overall setup parameters for IPSEC, which apply to all connections. In our example file, it is:
    # basic configuration
    config setup
    	# THIS SETTING MUST BE CORRECT or almost nothing will work;
    	# %defaultroute is okay for most simple cases.
    	# Debug-logging controls:  "none" for (almost) none, "all" for lots.
    	# Use auto= parameters in conn descriptions to control startup actions.
    The variables set here are:
    Tells the KLIPS IPSEC code in the Linux kernel which interface to use. In many cases, the appropriate interface is just your default connection to the world (the Internet, or your corporate network). In these cases, you can use the default setting:
    • interfaces=%defaultroute

    In other cases, you can name one or more specific interfaces to be used by FreeS/WAN. For example:

    • interfaces="ipsec0=eth0"
    • interfaces="ipsec0=eth0 ipsec1=ppp0"
    Both tell KLIPS to use eth0 as ipsec0. The second one also supports IPSEC over PPP.

    The interfaces specified here are the only ones this gateway machine can use to communicate with other IPSEC gateways. If this is not correct, nothing works.

    If you need to discover interface names, use the command:

    If you have PCMCIA or other interfaces that are not available at boot time, special measures are required. See our Configuration document.
    Debugging setting for the KLIPS kernel code
    Debugging setting for the Pluto key and connection negotiation daemon.
    List of connections to be automatically loaded into memory when Pluto starts.
    List of connections to be automatically started into memory when Pluto starts.

    plutoload and plutostart can be quoted lists of connection names, but are often set to %search as in our example. Any connection with auto=add in its connection definition is then loaded, and any connection with auto=start is started.

    Editing connections in /etc/ipsec.conf

  6. The easiest way to create a connection is by editing one of our examples, either the one in the /etc/ipsec.conf file or one from our doc/examples file.
    Connection defaults
    There is a special name %default that lets you define things that apply to all connections. e.g. our example file has:
    # defaults for subsequent connection descriptions
    conn %default
    	# How persistent to be in (re)keying negotiations (0 means very).
    	# Parameters for manual-keying testing (DON'T USE OPERATIONALLY).
    Variables set here are:
    How persistent to be in (re)keying negotiations (0 means very).

    For testing, you might wish to set this to 10 or even 1 to avoid wasting resources on incorrectly set up connections. In production, it is often set to zero (retry forever); keeping the connection up is what machine resources are for.

    A number needed the manual keying code. Any hex number ending in zero will do.
    Options for ESP (Encapsulated Security Payload), the usual IPSEC encryption mode. Settings here are for encryption using triple DES and authentication using MD5. Note that encryption without authentication should not be used; it is insecure.
    Key for ESP encryption.
    Key for ESP authentication.

    Note that the keys we supply here are intended only for testing. Testing is easier if everyone uses the same key, but these keys are utterly useless for security since any attacker with a grain of sense can be expected to discover them.

    For real use, you should go to automatic keying. If that is not possible, create your own keys for manual mode and keep them secret.

    Once you are finished testing, you should edit these defaults:

    • delete the test keys or comment them out with # characters
    • add anything that is standard for all gateways in your organisation
    • optionally, put auto=start in the default connection description to get all connections started automatically.

    Editing a connection description
    Choose an example connection (either from /etc/ipsec.conf or from our
    doc/examples file) that is similar to what you want to do. e.g. Use the subnet tunnel example if you have routable IP addresses for the client systems or the masqueraded tunnel example if not. Copy that example and rename it appropriately for the connection you would like to build: "fred-susan", "reno-van" or whatever. The name is the second string in the line that begins with "conn", for example in:
    	conn snt
    The connection name is "snt" and to define another connection you make a copy with a new name such as:
    	conn reno-van
    A sample connection description is:
    # sample tunnel (manually or automatically keyed)
    # "(manual)" means relevant only to manual keying, "(auto)" only to automatic.
    # For manual keying, we use ESP for both encryption and authentication, the
    # simplest and often the best method.
    # The network here looks like:
    #   leftsubnet====left----leftnexthop......rightnexthop----right====rightsubnet
    # If left and right are on the same Ethernet, omit leftnexthop and rightnexthop.
    conn sample
    	# left security gateway (public-network address)
    	# next hop to reach right
    	# subnet behind left (omit if there is no subnet)
    	# right s.g., subnet behind it, and next hop to reach left
    We omit here the variables we have shown as set in the default connection above. All of them could also be set here. If they are set in both places, settings here take precedence. Defaults are used only if the specific connection description has no value set.

    Many of the variables in this file come in pairs such as "leftsubnet: and "rightsubnet", one for each end of the connection. The variables on the left side are:

    The gateway's external interface, the one it uses to talk to the other gateway.
    Where left should send packets whose destination is right, typically the first router in the appropriate direction.

    This need not always be set. If:

    • either you have interfaces=%defaultroute
    • or the two gateways are directly linked, on the same wire
    then there is no need to tell the system the next hop. However, in all other cases, you must provide nexthop information. KLIPS (Kernel IP Security) bypasses the normal routing machinery, so you must give KLIPS the information even though routing already knows it.

    (Yes, we know that design is not ideal, and we plan to change it. See extensive discussions on the mailing list, mostly with "routing" in the subject lines.)

    Addresses for client machines left is protecting.
    • Often something like to indicate that a subnet resides behind left. This gives a tunnel mode connection.
    • If you omit this parameter (or set it to left's address and add a /32 netmask), then left is both the security gateway and the only client on that end.
    • For some applications, you may want to do both. You can create two connections, one to protect traffic from the subnet behind left and another to protect traffic from the left gateway itself.
    Note that a connection to a subnet behind left, such as 101.202.303.0/24, does not include left itself. It is a common error to attempt testing such a connection by pinging from left to the far end or vice versa. This does not work, even if the connection is functioning perfectly, since traffic to or from left itself is not sent on that connection. If you want to protect traffic originating or terminating on left, you need a separate tunnel for that in addition to the subnet's tunnel.
    Set to "yes" if the subnet behind left uses non-routable addresses and left does IP masquerade for them.
    If the conn setup section has plutoload=%search, then all connections marked auto=add are loaded when Pluto starts.

    If the conn setup section has plutostart=%search, then all connections marked auto=start are started when Pluto starts.

    There are corresponding right* parameters of course.

    Which is which?

    Which security gateway is "left" and which is "right" is arbitrary.

    We suggest that you name connections by their ends. For example, name the link between Fred and Susan's machines "fred-susan" or the link between your Reno and Vancouver offices "reno-van". You can then let "left" refer to the left half of the name, "fred" or "reno" in our examples, and "right" to the other half.

    Note that the names should be the same in the ipsec.conf files on both ends. The name "reno", for example, refers to the machine in Reno, no matter which city the file is in, and if "reno" is "left" in the reno-van description in Reno, then "reno" is "left" in that description on the Vancouver machine as well. When you copy the file from one machine to the other, the only change you should make on the second machine is changing the interfaces= line to match the interface the second machine uses for IPSEC.

    In general, you should use numeric IP addresses, not names, here. The file syntax allows names to be used, but this creates an additional risk. If someone can subvert the DNS service, then they can redirect packets whose addresses are looked up via that service.

    The "nexthop" parameters are not needed if the two gateways are directly connected to each other, or for a machine which has interfaces=%defaultroute. Otherwise they are the addresses of the next network gateways on both ends. For example, if the network is like this:


    and West is "left", then leftnexthop=Westgate and rightnexthop=Eastgate.

    Creating keys with ranbits

    Notice that at this point you may have two connections with identical keys, the one you copied and the one you just created. This creates a potential security hole. If you ever use the duplicate keys on two different connections, then either of the remote admins can read traffic destined for the other's system. Delete one copy of the key material now to avoid any risk of inadvertently doing that.

    You can create new random keys with the ranbits(8) utility. For example, the commands:

          umask 177
          ipsec ranbits 192  > temp
          ipsec ranbits 128 >> temp
    create keys in the sizes needed for our default algorithms:

    • 192-bit key for 3DES encryption
      (only 168 bits are used; parity bits are ignored)
    • 128-bit key for keyed MD5 authentication

    If you want to use SHA instead of MD5, that requires a 160-bit key

    Note that any temporary files used must be kept secure since they contain keys. That is the reason for the umask command above. The temporary file should be deleted as soon as you are done with it. You may also want to change the umask back to its default value after you are finished working on keys.

    The ranbits utility may pause for a few seconds if not enough entropy is available immediately. See ipsec_ranbits(8) and random(4) for details.

    Putting secrets in /etc/ipsec.secrets

    This file stores the secrets used to authenticate communication for the Diffie-Hellman key exchange in the IKE protocol.

    Each line has the IP addresses of the two gateways plus the secret. It should look something like this:	"0xf568175c_97462413_6db3d6ae_f2b46f40_d4e891fc_99d422f4_d6160755_0410164c"
    This shows a secret generated by our ipsec ranbits which produces a hexadecimal string as output. Note that the quotes are required. You can use any character string as your secret. For security, it should be both long and extremely hard to guess.

    For details, see the ipsec.secrets(5) man page.

    You want the same secret on the two gateways used, so you create a line with that secret and the two gateway IP addresses.

    The installation process supplies an example secret, useful only for testing. You should change it for production use. To create a new secret, use:

          umask 177
          ipsec ranbits 256  > temp
    Remember to delete the temporary file.
  7. Copy the two files:

    • /etc/ipsec.conf
    • /etc/ipsec.secrets

    to the other gateway machine by some secure means.

    Don't just FTP or mail these files! It is vital that the keys in /etc/ipsec.conf and the secrets in /etc/ipsec.secrets remain secret. An attacker who knew those could easily have all the data on your "secure" connection. Carry the files on a floppy, and lock the floppy in a good safe or erase it extremely thoroughly afterward. Or use PGP or SSH to make the transfer.

    Note also that those files should be owned by root. /etc/ipsec.secrets should have permissions rw-------.

    If /etc/ipsec.conf contains keys, then it too should have permissions rw-------. In production use, it will not normally contain keys; the keys are automatically generated.

    Note that /etc/ipsec.conf is installed with permissions rw-r--r--. If you plan to use manually keyed connections for anything more than initial testing, you must:

    • either change permissions to rw-------
    • or store keys separately in secure files and access them via include statements in /etc/ipsec.conf. See our configuration document.

    Setting up interfaces

  8. For now, these files don't have to be changed much. They should be identical on the two gateways, except that each gateway must have the correct interfaces setting in its copy of /etc/ipsec.conf. This is in the file section labelled by the line config setup.

    For now, all you need to do in the overall config setup section of the file is set interfaces. We cover other options in our Configuration document. When you go to three or more gateways, however, you should ensure that distribution of keys and secrets is kept to a minimum. If Reno, Vancouver and Munich offices all communicate, there is no reason to give Reno keys to the Vancouver-Munich tunnel, for example.

    Matching numbers

    It is important that the numbers here match the network configuration. Suppose you are at the Reno office and your ipsec.conf file now has, among others, these lines:
    config setup
    conn reno-van
    When you tell FreeS/WAN to start the reno-van connection, it doesn't automagically know that it is in Reno, or that it is "left" in the configuration. It discovers that by comparing the IP address for ipsec0 (and, if it is set, for ipsec1) to the addresses for left and right. ipsec0 inherits its address from the underlying device, eth0 in our example.

    So in our example, if eth0 has IP address then ipsec0 inherits that address, the correct match is found, and this FreeS/WAN discovers that it is left. It then sets itself up with the other left* parameters

    The next hop on the path from left to right. In many applications this will be a router at left's ISP. For an IPSEC gateway to a departmental LAN, the next hop might be a router on the corporate LAN.
    Subnet address for clients behind left, with netmask. Often something like:
    This can be omitted if there is no subnet, if left is acting as its own gateway.
    Set to yes if left is masquerading for its clients.
    Once it has these parameters, FreeS/WAN sets things so that
    • packets from leftsubnet addressed to rightsubnet are routed through a tunnel to right.
    • Packets for leftsubnet can be received on the tunnel and delivered.
    All should be well.

    Of course, there must also be an interface and routes set up so that this machine can exchange non-IPSEC packets with clients on leftsubnet. This is done with standard Linux utilities such as ifconfig(8) and route(8). Also, things must be correct on right in Vancouver; it takes two to tunnel.

    A data mismatch anywhere in this configuration will cause FreeS/WAN to fail and to log various error messages. Depending on just how confused FreeS/WAN is and about what, the error messages may be somewhat confusing. See our problem reporting file to get help interpreting them if required.

    We recommend double-checking for consistency here before continuing.

    Testing the installation

  9. Reboot both gateways to get FreeS/WAN started. No connections are actually made yet, but the stage is set.

    Examine /var/log/messages for any signs of trouble.

    On both gateways, the following entries should now exist in the /proc/net/ directory:

    • ipsec_eroute
    • ipsec_spi
    • ipsec_spigrp
    • ipsec_spinew
    • ipsec_tncfg
    • ipsec_version

    and the IPSEC interfaces should be attached on top of the specified physical interfaces. Confirm that with:

    	cat /proc/net/ipsec_tncfg

    You should see at least device ipsec0. Routing connections through this pseudo-device with our eroute(8) utility causes the data to be encrypted before being delivered to the underlying network interface.

    Minor confusion sometimes arises when people find that /dev/ipsec0, and /dev/ipsec1 are not visible with 'ls'. This is as it should be. Other network pseudo-devices such as eth0 and eth1 do not have entries in /dev either. In general, network devices do not need such entries.

    Manually keyed test

    The initial tests should be done with manually keyed connections. This lets you test the lower-level parts of Linux FreeS/WAN (mainly the KLIPS code which you've added to your kernel) while bypassing the higher-level parts. We will get to those once we're sure the low level works right.

  10. On one gateway, start IPSEC with:

    	ipsec manual --up name
    replacing name with the connection name you used in /etc/ipsec.conf.

    If it doesn't generate any errors, do

    	ipsec look

    and see if the output looks something like this: Wed Nov 25 22:51:45 EST 1998
    ------------------------- -> => tun0x200@ esp0x202@
    tun0x200@ IPv4_Encapsulation: dir=out ->
    esp0x203@ 3DES-MD5-96_Encryption: dir=in  iv=0xc2cbca5ba42ffbb6  seq=0  bit=0x00000000  win=0  flags=0x0<>
    esp0x202@ 3DES-MD5-96_Encryption: dir=out  iv=0xc2cbca5ba42ffbb6  seq=0  bit=0x00000000  win=0  flags=0x0<>
    Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface   U      1500 0          0 eth1   UG     1404 0          0 ipsec0

    If it does, you're probably in business.

    This example shows:

    	a tunnel              tun0x200 going to
    	outgoing connection   esp0x202
    	incoming connection   esp0x203
    Both connections use ESP with 3DES encryption and MD5 authentication.

    The routing is:    via eth1 and the Internet    via ipsec0 which encrypts and then sends to
    This routes all traffic to the protected network through an IPSEC tunnel to the gateway

  11. A manual connection must be set up on both ends to work. So give the same commands:
    	ipsec manual --up name
    	ipsec look

    on the other gateway and look for similar results.

  12. If that works, test whether Sunrise can ping Sunset and vice versa. It is not enough to just test that East can ping West; the goal is to secure traffic between the subnets, not between the security gateways themselves.

    In general, pings or other tests using the public interfaces of East and/or West are entirely useless. The IPSEC tunnel is for packets between the two protected subnets and the outside interfaces are not on those subnets. Depending on your routing configuration, test packets sent via those interfaces will be:

    • either transmitted in the clear, bypassing the tunnel,
    • or discarded because there is no tunnel in place to handle them
    In either case, they tell you nothing about the tunnel.

    Sometimes it will be inconvenient to use the client machines (Sunrise and Sunset in our example) for testing. In these cases, use a command such as:

         traceroute -i eth0 -f 20
    where each of the interfaces specified (eth0 and in the example) are on one of the protected subnets, eth0 being the local gateway's interface on that side and the remote gateway's subnet interface. This forces the packets through the IPSEC tunnel you want to test.

    For information on setting things up so that gateways can do IPSEC to each other or to remote subnets, see our configuration document.

    If you have other software set up, test with it as well. Telnet from Sunrise to Sunset, browse a web server on the remote net and so on.

    Testing with tcpdump

  13. To verify that all is working, run tcpdump(8) on a machine which can listen to the traffic between the gateways.

    This really has to be done from a third machine, not from one of the gateways. On the gateways you'll see packets at intermediate stages of processing and the result will be confusing. Also, both tcpdump(8) and nmap(8) use the libpcap library. That library does not recognise ipsec? devices and will generate "bad physical medium" error messages if you try to use it with them.

    The packets should, except for some of the header information, be utterly unintelligible. The output of good encryption looks exactly like random noise.

    You can put recognizable data in the ping packets with something like:

    	ping -p feedfacedeadbeef
    "feedfacedeadbeef" is a legal hexadecimal pattern that is easy to pick out of hex dumps.

    For many other protocols, you need to check if you have encrypted data or ASCII text. Encrypted data has approximately equal frequencies for all 256 possible characters. ASCII text has most characters in the printable range 0x20-0x7f, a few control characters less than 0x20, and none at all in the range 0x80-0xff.

    0x20, space, is a good character to look for. In normal English text space occurs about once in seven characters, versus about once in 256 for random or encrypted data. You can put long sequences of spaces in your data and look for 0x20202020 in output, but this is not usually necessary.

    If packets look like total garbage, nothing recognizable, all is well.

    Testing Automatic connections

  14. Do
    	ipsec manual --down name
    on both gateways. This shuts down the named tunnel. You can verify with the same commands used to check it was up:
    	ps -ax
    	ipsec look

  15. Now, do
    	ipsec auto --add name
    on both gateway machines. Then do:
    	ipsec auto --up name
    on one gateway. The first command adds the information on this connection to Pluto's database. The second makes the connection active.

    Note that to shut down a connection, you must do:

    	ipsec auto --down name
    on both gateway machines, even though you only start it from one.

    Again, you can verify with the same commands.

    Repeat the ping test. Repeat the tcpdump test.

    If everything succeeds, congratulations.

    You now have a working Linux FreeS/WAN installation.

    For information on configuring the system for production use, see our Configuration document.

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