More complex requirements are covered elsewhere:
However, please read this quick start section first , before tackling the others.
There are two easy ways to install FreeS/WAN:
If you are using one of them, just include FreeS/WAN in the choices you make during installation, or add it to your configuration later using the distribution's tools.
Sources for RPM packages of FreeS/WAN are:
You need to download at least two RPMs:
Once you have them, install the RPMs with rpm -i commands. You will need to be root to install the kernel.
If your distribution does not include FreeS/WAN and no RPMs are available, see our installation from source document.
That's it. FreeS/WAN is installed.
RSA is a public key cryptographic technique. Keys are created as matched pairs. Each pair includes:
For FreeS/WAN, both keys for your system are in the ipsec.secrets(5) file. Maintaining security of this file is essential since it holds your private key.
To generate your key pair, give these commands as root:
ipsec newhostkey > /etc/ipsec.secrets chmod 600 /etc/ipsec.secrets
Key generation may take some time, even on a fast system. Also, it
needs a lot of random numbers so you
may need to switch consoles and do something like typing a lot of text
The RSA keys we generate are suitable only for authentication, not for encryption. IPsec uses them only for authentication. See our IPsec section for details.
Opportunistic encryption makes setup and adminstration of IPsec simple.
For opportunistic encryption, you do not need to communicate with the administrator of a site before establishing secure communications to that site. In particular, you do not have to send them your keys or collect and authenticate theirs. All you have to do is set up your end correctly and from there on, everything is automatic.
In this section, we treat the simplest case:
There are two steps:
Once this is done, your system will automatically encrypt whenever it can.
# general IPsec setup config setup # Use the default interface interfaces=%defaultroute # Use auto= parameters in conn descriptions to control startup actions. plutoload=%search plutostart=%search # defaults for subsequent connection descriptions conn %default # How to authenticate gateways authby=rsasig # Try to start all connections by default auto=start # description for opportunistic connections conn us-to-anyone also=our_stuff # our system details, stored below left=%opportunistic # anyone we can authenticate via DNS rekey=no # let unused connections die # description of our system # included in other connection descriptions via also= lines # must come after the lines that use it conn our_stuff # all connections should use our default route # also controls the source address on IPsec packets right=%defaultroute # our identity for IPsec negotiations # must match what is in DNS and ipsec.secrets(5) rightid=xy.example.com
The last line above is the only one that you need to edit for your system. All the rest is identical for any standalone machine doing opportunistic encryption.
There is no need to provide any keys in this file. Your private key is in ipsec.secrets(5) and, for opportunistic encryption, the public keys for remote gateways are all looked up in DNS.
What follows here is a simple technique suitable for systems which always initiate any opportunistic encryption they are involved in. If you need to let others inititiate -- for example, if you run services on your machine and want remote clients to be able to acess them securely -- then you need the more complex techniques described in the gateways section.
For example, a reverse lookup on the IP address for a home gateway might give 123.adsl.kalamazoo.example.net, and a forward lookup for example.dyndns.org might point to that gateway. You could use either of these names as your ID for IPsec purposes, if the admins at either example.net or dyndns.org co-operate.
If not, you can use any domain whose DNS adminstrator is willing to help out. You do not need an A record (address record, associating your chosen name with an address) in that domain, only a KEY record.
You can generate a DNS KEY record containing your system's public key with the command:
ipsec showhostkeyThe 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/
The name here is taken from ipsec.secrets(5). If it is not what you want, edit that file to correct it, then run ipsec showhostkey again.
The name must also match what you used for rightid= in ipsec.conf(5).
Give this record to the DNS administrator, for insertion into the zone file of the domain.
There are two steps in the setup. Setting up your ipsec.conf(5) for this is quite simple. Setting up the DNS entries to support it is a bit more complex.
You need only make a few additions to in the ipsec.conf(5) file to expand from a standalone system (which protects only its own traffic) to a gateway (which protects traffic for other systems):
A few other things in ipsec.conf(5) will be changed as well in our example:
With those changes, the ipsec.conf(5) file is:
# general IPsec setup config setup # Use the default interface interfaces=%defaultroute # Use auto= parameters in conn descriptions to control startup actions. plutoload=%search plutostart=%search # defaults for subsequent connection descriptions conn %default # How to authenticate gateways authby=rsasig # Default is to load all connection descriptions # but not try to start the connection # Some conns may over-ride this with auto=start auto=add # opportunistic connections to our gateway conn us-to-anyone also=gate_stuff # our system details, stored below right=%opportunistic # anyone we can authenticate via DNS rekey=no # let unused connections die # opportunistic connections for client systems # our gateway will build opportunistic tunnels on behalf of any # machine in the specified subnet conn subnet-to-anyone also=gate_stuff # our system details, stored below also=public_subnet # subnet description, below right=%opportunistic # anyone we can authenticate via DNS rekey=no # let unused connections die # description of our gateway system # included in other connection descriptions via also= lines # must come after the lines that use it conn gate_stuff # all connections should use our default route # also controls the source address on IPsec packets left=%defaultroute # our identity for IPsec negotiations # must match what is in DNS and ipsec.secrets(5) leftid=gateway.example.com # description of the subnet this gateway encrypts for # numbers used here are arbitrary, just for example conn public_subnet leftsubnet=22.214.171.124/24
# opportunistic connections for additional systems conn second-to-anyone also=gate_stuff # our system details, stored below also=second_subnet # subnet description, below right=%opportunistic # anyone we can authenticate via DNS rekey=no # let unused connections die # description of a second subnet this gateway encrypts for # numbers used here are arbitrary, just for example conn second_subnet leftsubnet=126.96.36.199/24
There is one small thing to be careful of here. An also= line must appear in the file before the conn it references, so the first section above must appear before conn gate_stuff.
The subnets used in these descriptions need not correspond to physical subnets. This is discussed in more detail in our advanced configuration document.
DNS setup for an opportunistic gateway involves several types of record:
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 gateway.example.com. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/This can be generated with ipsec showhostkey.
The record you need looks like this:
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 188.8.131.52.in-addr.arpa. IN KEY 0x4200 4 1 AQOF8tZ2...+buFuFn/
Generate a record with
As always, IP addresses in the reverse map are written backwards. In the above example, the gateway IP address is 184.108.40.206.
; RSA 2048 bits gateway.example.com Sat Apr 15 13:53:22 2000 IN TXT "X-IPsec-Server(10)=220.127.116.11 AQOF8tZ2...+buFuFn/"This record must be generated on the gateway so it can get the key from ipsec.secrets(5). The command is:
ipsec showhostkey --txt 18.104.22.168You must supply the gateway IP address on the command line.
One of these records is required in the reverse map for each system using this gateway for opportunistic IPsec.
A common requirement is for pre-configured connections between a specfic network and some set of remote machines. For example, an office network will often need to provide remote access services for:
We refer to the remote machines as "Road Warriors". For purposes of IPsec, anyone with a dynamic IP address is a road warrior.
Of course, if both the warrior and the gateway at the office are set up for opportunistic encryption, then you may not need the pre-configured connection. Here we assume that you do need it. For example:
This section has three sub-sections:
On either end, the opportunistic setup is unaffected by this. You leave it in place so both systems can continue to do opportunistic encryption with everyone but each other.
To set up an explicitly configured connection, you need some information about the system on the other end.
The gateway adminstrator needs to know some things about each Road Warrior:
To get this information, in a format suitable for insertion directly into the gateway's ipsec.conf(5) file, issue this command on the Warrior machine:
ipsec showhostkey --rightThe output should look like this (with the key shortened for easy reading):
The Road Warrior needs to know:
This information should be provided in a convenient format, ready for insertion in the Warrior's ipsec.conf(5) file. For example:
left=22.214.171.124 leftsubnet=126.96.36.199/24 leftid=gateway.example.com leftrsasigkey=
The gateway administrator typically needs to generate this only once. The same file can be given to all Warriors.
Of course it is also possible to provide different versions (in particular, access to differnet subnets) to different groups of Warriors. See our advanced configuration document.
To set up a Road Warrior machine, we start from the opportunistic client setup shown above. We need not change anything there, only add a connection description for the pre-configured tunnel.
# pre-configured link to office network conn us-to-office also=our_stuff # our system details, stored below # # information obtained from office system admin # goes to the right of the = signs in these lines # values shown here are just for example # left=188.8.131.52 # gateway IP address leftsubnet=184.108.40.206/24 # the office network leftid=gateway.example.com # real keys are much longer than shown here leftrsasigkey=
Everything else remains as it was when we had only opportunistic connections.
We could easily add more connections as required, perhaps one each for his office, her office, the kid's school, ... The file would grow longer, but nothing already in the file would need to change.
If your gateway uses NAT to allow machines to access the Internet without having their own routable IP addresses, then from the point of view of anyone else on the Internet:
Firewall rules do need to be a little more complex to support the NAT. See the firewall section below for details.
For a more detailed discussion of NAT, see our background section.
Adding road warrior support so people can connect remotely to your office network is straightforward.
We start from the opportunistic gateway setup shown above.
Instead, we suggest you give each warrior its own file, choosing some directory and naming convention that suits your system and style.
For this example, we use the directory /etc/ipsec.road and use filenames based on IPsec ID, so the Warrior using ID xy.example.com gets a file named xy.conf.
Using such files, you need add only one line to ipsec.conf(5). With our naming convention, the line is:
FreeS/WAN will then read all those files and behave as if they were part of the ipsec.conf(5) file.
This needs to come before the conn gate_stuff section, so that the Warriors' connection descriptions can use also=gate_stuff. A convenient place for the line is right after the conn %default section.
Each of the Road Warrior files then contains a connection description for that Warrior. For example:
# connection description for Road Warrior "xy" conn gate-xy # use the gateway description in ipsec.conf(5) also=gate_stuff # allow connection attempt from any address # attempt fails if caller cannot authenticate right=%any # authentication information rightid=xy.example.com rightrsasigkey=
With this technique, it becomes fairly simple to administer a gateway that supports many Road Warriors. For example:
To add a new user, simply add a suitable file.
To disable an account -- for example if a key is compromised -- first remove the file, then take any existing connection down with:
ipsec auto --down connectionand delete it from Pluto's internal database with:
ipsec auto --delete connection
If you have many users, it would be worthwhile to write scripts to automate such tasks.
Of course, if both offices are set up for opportunistic encryption and the security policies in place allow you to use that, explicitly configured tunnels become unnecessary. However, this will not always be the case.
Of course, a network-to-network tunnel requires its own connection description, so you have to add that. There are two ways to do this.
# sample tunnel # 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) left=10.0.0.1 # next hop to reach right leftnexthop=10.44.55.66 # subnet behind left (omit if there is no subnet) leftsubnet=172.16.0.0/24 # right s.g., subnet behind it, and next hop to reach left right=10.12.12.1 rightnexthop=10.88.77.66 rightsubnet=192.168.0.0/24 auto=startDue to an unfortunate interaction between FreeS/WAN and the kernel routing code, you must specify leftnexthop (the router which left sends packets to in order to get them delivered to right) and rightnexthop (vice versa).
The *nexthop parameters will be eliminated in a future release, but perhaps not soon. We know they should go, but getting them out is not a simple problem. For now, live with them.
This description can be generated on either machine and simply inserted in the ipsec.conf(5) file on the other. No change is required or desired.
When using left=%defaultroute, you do not need to specify leftnexthop. left does not need to know rightnexthop either, so on left the connection description can be:
conn sample # left security gateway (public-network address) left=%defaultroute # subnet behind left (omit if there is no subnet) leftsubnet=172.16.0.0/24 # right s.g., subnet behind it right=10.12.12.1 rightsubnet=192.168.0.0/24 auto=startOn right it is:
conn sample # left security gateway (public-network address) left=10.0.0.1 # subnet behind left (omit if there is no subnet) leftsubnet=172.16.0.0/24 # right s.g., subnet behind it right=%defaultroute rightsubnet=192.168.0.0/24 auto=start
This section describes simple firewall setups, suitable for getting a FreeS/WAN machine running. A separate FreeS/WAN and firewalls document provides more detail.
The first step is to allow IPsec packets (IKE on UDP port 500 plus ESP, protocol 50) in and out of your gateway. A script to set up iptables(8) rules for this is:
# edit this line to match the interface you use as default route # ppp0 is correct for many modem, DSL or cable connections # but perhaps not for you world=ppp0 # # allow IPsec # # IKE negotiations iptables -A INPUT -p udp -i $world --sport 500 --dport 500 -j ACCEPT iptables -A OUTPUT -p udp -o $world --sport 500 --dport 500 -j ACCEPT # ESP encrypton and authentication iptables -A INPUT -p 50 -i $world -j ACCEPT iptables -A OUTPUT -p 50 -o $world -j ACCEPT
Optionally, you could restrict this, allowing these packets only to and from a list of known gateways.
A second firewalling step -- access controls built into the IPsec protocols -- is automatically applied:
Optionally, you can add a third step using whatever additional firewall rules are required for your situation. These rules can recognise packets emerging from IPsec. They are marked as arriving on an interface such as ipsec0, rather than eth0, ppp0 or whatever. For example, in an iptables(8) rule set, you would use:
However, on a gateway there are additional things to do:
You need additional rules to handle these things. For example, adding some rules to the set shown above we get:
# edit this line to match the interface you use as default route # ppp0 is correct for many modem, DSL or cable connections # but perhaps not for you world=ppp0 # # edit these lines to describe your internal subnet and interface localnet=220.127.116.11/24 internal=eth1 # # allow IPsec # # IKE negotiations iptables -A INPUT -p udp -i $world --sport 500 --dport 500 -j ACCEPT iptables -A OUTPUT -p udp -o $world --sport 500 --dport 500 -j ACCEPT # ESP encrypton and authentication iptables -A INPUT -p 50 -i $world -j ACCEPT iptables -A OUTPUT -p 50 -o $world -j ACCEPT # # packet forwarding for an IPsec gateway # # handle packets emerging from IPsec # ipsec+ means any of ipsec0, ipsec1, ... iptables -A FORWARD -d $localnet -i ipsec+ -j ACCEPT # simple rule for outbound packets # let local net send anything # IPsec will encrypt some of it iptables -A FORWARD -s $localnet -i $internal -j ACCEPT
On a production gateway, you would no doubt need tighter rules than the above. For details, see: