.\" $OpenBSD: vpn.8,v 1.26 1999/10/07 20:50:30 angelos Exp $ .\" Copyright 1998 Niels Provos .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by Niels Provos. .\" 4. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" Manual page, using -mandoc macros .\" .Dd February 9, 1999 .Dt VPN 8 .Os .Sh NAME .Nm vpn .Nd configuring the system for virtual private networks .Sh DESCRIPTION A virtual private network is used to securely connect two or more subnets over the internet. For each subnet there is a security gateway which is linked via a cryptographically secured tunnel to the security gateway of the other subnet. .Xr ipsec 4 is used to provide the necessary network-layer cryptographic services. This document describes the configuration process for setting up a .Nm VPN . .Pp Briefly, creating a VPN consists of the following steps: .Pp .Bl -enum -compact .It Choose a key exchange method: manual keyed or .Xr photurisd 8 . .It Create a Security Association (SA) for each endpoint. .It Create the appropriate IPSec flows. .It Configure your firewall rules appropriately. .El .Ss Choosing a key exchange method There are currently two key exchange methods available: .Pp .Bl -bullet -inset -compact .It manual (symmetric shared secret) .It .Xr photurisd 8 .El .Pp At present VPNs between private (RFC 1918) networks must use manual keying, as .Xr photurisd 8 can only be used if the IP address of the security gateway actually falls within the range of addresses being tunnelled to. This can clearly never occur if the addresses being tunnelled to are non-routable private networks. .Ss Generating Manual Keys The shared secret symmetric keys used to create a VPN can be any hexadecimal value, so long as both sides of the connection use the same values. Since the security of the VPN is based on these keys being unguessable, it is very important that the keys be chosen using a strong random source. One practical method of generating them is by using the .Xr random 4 device. To produce 160 bits of randomness, for example, do a: .Bd -literal dd if=/dev/urandom bs=1024 count=1 | sha1 .Ed .Pp Different cipher types may require different sized keys. .Pp .Bl -column "Cipher" "Key Length" -compact .It Em Cipher Key Length .It Li DES Ta "56 bits" .It Li 3DES Ta "168 bits" .It Li BLF Ta "Variable (160 bits recommended)" .It Li CAST Ta "Variable (160 bits recommended)" .It Li SKIPJACK Ta "80 bits" .El .Pp Use of DES or SKIPJACK as an encryption algorithm is not recommended (except for backwards compatibility) due to their short key length. Furthermore, recent attacks on SKIPJACK have shown severe weaknesses in its structure. .Pp Note that DES requires 8 bytes to form a 56-bit key and 3DES requires 24 bytes to form its 168-bit key. This is because the most significant bit of each byte is ignored by both algorithms. .Ss Enabling the Appropriate Kernel Operations .Xr ipsec 4 operations must be first enabled using .Xr sysctl 8 . Before creating security associations, or performing encryption (ESP) or authentication (AH) operation, ensure the appropriate kernel operation has been enabled: .Bd -literal sysctl -w net.inet.esp.enable=1 sysctl -w net.inet.ah.enable=1 .Ed .Pp For more permanent operation, these options should be enabled in your .Xr sysctl.conf 5 . .Pp .Ss Creating Security Associations Before the IPSec flows can be defined, two Security Associations (SAs) must be defined on each end of the VPN, e.g.: .Bd -literal ipsecadm new esp -spi SPI_OUT -src A_EXTERNAL_IP -dst B_EXTERNAL_IP -forcetunnel -enc 3des -auth sha1 -key ENCRYPTION_KEY -authkey AUTHENTICATION_KEY ipsecadm new esp -spi SPI_IN -src B_EXTERNAL_IP -dst A_EXTERNAL_IP -forcetunnel -enc 3des -auth sha1 -key ENCRYPTION_KEY -authkey AUTHENTICATION_KEY .Ed .Pp .Ss Creating IPSec Flows Both IPsec gateways need to configure .Xr ipsec 4 routes with the .Xr ipsecadm 8 tool: .Pp On the security gateway of subnet A: .Bd -literal ipsecadm flow -dst B_EXTERNAL_IP -spi SPI_OUT -proto esp -addr A_EXTERNAL_IP 255.255.255.255 B_EXTERNAL_IP 255.255.255.255 -local ipsecadm flow -dst B_EXTERNAL_IP -spi SPI_OUT -proto esp -addr A_INTERNAL_NETWORK A_INTERNAL_NETMASK B_INTERNAL_NETWORK B_INTERNAL_NETMASK ipsecadm flow -dst B_EXTERNAL_IP -spi SPI_OUT -proto esp -addr A_EXTERNAL_IP 255.255.255.255 B_INTERNAL_NETWORK B_INTERNAL_NETMASK -local ipsecadm flow -dst B_EXTERNAL_IP -spi SPI_OUT -proto esp -addr A_INTERNAL_NETWORK A_INTERNAL_NETMASK B_EXTERNAL_IP 255.255.255.255 .Ed .Pp and on the security gateway of subnet B: .Bd -literal ipsecadm flow -dst A_EXTERNAL_IP -spi SPI_IN -proto esp -addr B_EXTERNAL_IP 255.255.255.255 A_EXTERNAL_IP 255.255.255.255 -local ipsecadm flow -dst A_EXTERNAL_IP -spi SPI_IN -proto esp -addr B_INTERNAL_NETWORK B_INTERNAL_NETMASK A_INTERNAL_NETWORK A_INTERNAL_NETMASK ipsecadm flow -dst A_EXTERNAL_IP -spi SPI_OUT -proto esp -addr B_EXTERNAL_IP 255.255.255.255 A_INTERNAL_NETWORK A_INTERNAL_NETMASK -local ipsecadm flow -dst A_EXTERNAL_IP -spi SPI_OUT -proto esp -addr B_INTERNAL_NETWORK B_INTERNAL_NETMASK A_EXTERNAL_IP 255.255.255.255 .Ed .Pp Furthermore, unless manual keying is used, both security gateways need to start the .Xr photurisd 8 key management daemon with the .Fl v flag and make sure it is configured properly on both sides to provide the required security services (typically, encryption and authentication). .Ss Configuring Firewall Rules .Xr ipf 8 needs to be configured such that all packets from the outside are blocked by default. Only successfully IPSec-processed packets (from the .Xr enc0 4 interface), or key management packets (for .Xr photurisd 8 , .Tn UDP packets with source and destination ports of 468) should be allowed to pass. .Pp The .Xr ipf 5 rules for a tunnel which uses encryption (the ESP IPsec protocol) and .Xr photurisd 8 on security gateway A might look like this: .Bd -literal # ne0 is the only interface going to the outside. block in log on ne0 from any to any block out log on ne0 from any to any block in log on enc0 from any to any # Passing in encrypted traffic from security gateways pass in proto esp from gatewB/32 to gatewA/32 pass out proto esp from gatewA/32 to gatewB/32 # Passing in traffic from the designated subnets. pass in on enc0 from netB/netBmask to netA/netAmask # Passing in Photuris traffic from the security gateways pass in on ne0 proto udp from gatewB/32 port = 468 to gatewA/32 port = 468 pass out on ne0 proto udp from gatewA/32 port = 468 to gatewB/32 port = 468 .Ed .Pp If there are no other .Xr ipf 5 rules, the "quick" clause can be added to the last three rules. .Sh EXAMPLES To create a manual keyed VPN between two class C networks using 3DES encryption and the following IP addresses: .Pp .Bd -literal A_INTERNAL_IP = 10.0.50.1 A_EXTERNAL_IP = 192.168.1.254 B_EXTERNAL_IP = 192.168.2.1 B_INTERNAL_IP = 10.0.99.1 .Ed .Pp .Bl -enum .It Choose the shared secrets using a suitably random method: .Pp .Bd -literal # dd if=/dev/urandom bs=1024 count=1 | sha1 cd28c327c7fd0943596a96cc7bf9108cd896f33c # dd if=/dev/urandom bs=1024 count=1 | sha1 44aedc8aa8acf0b8c74acd626cd1b1057fb12c76 # dd if=/dev/urandom bs=1024 count=1 | sha1 c9fff55b501206a6607fb45c392c5e1568db2aaf .Ed .Pp .It Create the Security Associations (on both endpoints): .Pp .Bd -literal # /sbin/ipsecadm new esp -src 192.168.2.1 -dst 192.168.1.254 \e\ -forcetunnel -spi 1000 -enc 3des -auth sha1 \e\ -key 596a96cc7bf9108cd896f33c44aedc8aa8acf0b8c74acd62 \e\ -authkey c9fff55b501206a6607fb45c392c5e1568db2aaf # /sbin/ipsecadm new esp -src 192.168.1.254 -dst 192.168.2.1 \e\ -forcetunnel -spi 1001 -enc 3des -auth sha1 \e\ -key 596a96cc7bf9108cd896f33c44aedc8aa8acf0b8c74acd62 \e\ -authkey c9fff55b501206a6607fb45c392c5e1568db2aaf .Ed .Pp .It Create the ipsec route on machine A: .Pp .Bd -literal # /sbin/ipsecadm flow -dst 192.168.2.1 -spi 1001 -proto esp \e\ -addr 192.168.1.254 255.255.255.255 \e\ 192.168.2.1 255.255.255.255 -local # /sbin/ipsecadm flow -dst 192.168.2.1 -spi 1001 -proto esp \e\ -addr 10.0.50.0 255.255.255.0 10.0.99.0 255.255.255.0 # /sbin/ipsecadm flow -dst 192.168.2.1 -spi 1001 -proto esp \e\ -addr 192.168.1.254 255.255.255.255 \e\ 10.0.99.0 255.255.255.0 -local # /sbin/ipsecadm flow -dst 192.168.2.1 -spi 1001 -proto esp \e\ -addr 10.0.50.0 255.255.255.0 192.168.2.1 255.255.255.255 .Ed .It Create the ipsec flow on machine B: .Bd -literal # /sbin/ipsecadm flow -dst 192.168.1.254 -spi 1000 -proto esp \e\ -addr 192.168.2.1 255.255.255.255 \e\ 192.168.1.254 255.255.255.255 -local # /sbin/ipsecadm flow -dst 192.168.1.254 -spi 1000 -proto esp \e\ -addr 10.0.99.0 255.255.255.0 10.0.50.0 255.255.255.0 # /sbin/ipsecadm flow -dst 192.168.1.254 -spi 1000 -proto esp \e\ -addr 192.168.2.1 255.255.255.255 \e\ 10.0.50.0 255.255.255.0 -local # /sbin/ipsecadm flow -dst 192.168.1.254 -spi 1000 -proto esp \e\ -addr 10.0.99.0 255.255.255.0 192.168.1.254 255.255.255.255 .Ed .It Configure the firewall rules on machine A: .Bd -literal # ne0 is the only interface going to the outside. block in log on ne0 from any to any block out log on ne0 from any to any block in log on enc0 from any to any # Passing in encrypted traffic from security gateways pass in proto esp from 192.168.2.1/32 to 192.168.1.254/32 pass out proto esp from 192.168.1.254/32 to 192.168.2.1/32 # Passing in traffic from the designated subnets. pass in quick on enc0 from 10.0.99.0/24 to 10.0.50.0/24 .Ed .It Configure the firewall rules on machine B: .Bd -literal # ne0 is the only interface going to the outside. block in log on ne0 from any to any block out log on ne0 from any to any block in log on enc0 from any to any # Passing in encrypted traffic from security gateways pass in proto esp from 192.168.1.254/32 to 192.168.2.1/32 pass out proto esp from 192.168.2.1/32 to 192.168.1.254/32 # Passing in traffic from the designated subnets. pass in quick on enc0 from 10.0.50.0/24 to 10.0.99.0/24 .Ed .El .Sh FILES .Bl -tag -width /etc/photuris/photuris.conf -compact .It Pa /usr/share/ipsec/rc.vpn Sample VPN configuration file .It Pa /etc/photuris/photuris.conf Photuris configuration file .It Pa /etc/ipf.rules Firewall configuration file .El .Sh BUGS .Xr photurisd 8 can not be used in VPN mode unless both of the security gateway IP addresses lie within the network ranges being tunnelled to. In situations where the gateway IP is outside the desired netrange, such as with private (RFC 1918) networks, manual keying must be used. This should be fixed in the next release. .Sh SEE ALSO .Xr enc 4 , .Xr ipsec 4 , .Xr options 4 , .Xr ipf 5 , .Xr ipf 8 , .Xr ipsecadm 8 , .Xr isakmpd 8 , .Xr photurisd 8