IPsec

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This Provides an overview of IPsec in general. For information on the vtluug IPsec tunnel, see Infrastructure:IPsec

IPsec is a method of running an encrypted overlay network, so as to protect traffic originating from an unencrypted and/or untrusted network, such as a coffee shop's open WAP. It is among a number of other protocols which can be used. L2TP/IPsec is one of the most common methods, although OpenVPN and IKEv2 also are viable, faster, and arguably more secure methods. The latter is supported in openiked developed by the OpenBSD project. Most of this article assumes the use of IPsec/IKEv1

Network-to-Network

For purposes of this tutorial, we are setting up two endpoints, vpn1 and vpn2, both using IPv6 with the subnets 2001:db8:1::/64 and 2001:db8:2::/64, respectively.

Linux with OpenSWAN

Tested with OpenSWAN 2.6.41 on Arch Linux (updated on 2014-09-12).

  • Generate a new host key on both endpoints:
sudo ipsec newhostkey --output /etc/ipsec.secrets
  • Configure /etc/ipsec.conf on vpn1:
config setup
    protostack=netkey
    nat_traversal=off

conn vpn2
    authby=rsasig
    connaddrfamily=ipv6
    type=tunnel

    ike=aes256-sha2_256;modp2048
    phase2alg=aes256-sha2_256;modp2048
    sha2_truncbug=yes

    left=vpn1.example.com
    leftid=@vpn1.example.com
    leftsubnet=2001:db8:1::/64
    leftrsasigkey=0s...

    right=vpn2.example.com
    rightid=@vpn2.example.com
    rightsubnet=2001:db8:2::/64
    rightrsasigkey=0s...

    auto=start

Make sure to change leftrsasigkey to the public key of the RSA key that was generated in the above command, which can be found in /etc/ipsec.secrets. Replace rightrsasigkey with the RSA generated by the above command on the other endpoint, which can be found in the same location.

  • Configure /etc/ipsec.conf on vpn2:
config setup
    protostack=netkey
    nat_traversal=off

conn vpn1
    authby=rsasig
    connaddrfamily=ipv6
    type=tunnel

    ike=aes256-sha2_256;modp2048
    phase2alg=aes256-sha2_256;modp2048
    sha2_truncbug=yes

    left=vpn2.example.com
    leftid=@vpn2.example.com
    leftsubnet=2001:db8:2::/64
    leftrsasigkey=0s...

    right=vpn1.example.com
    rightid=@vpn1.example.com
    rightsubnet=2001:db8:1::/64
    rightrsasigkey=0s...

    auto=start

Make sure to change leftrsasigkey to the public key of the RSA key that was generated in the above command, which can be found in /etc/ipsec.secrets. Replace rightrsasigkey with the RSA generated by the above command on the other endpoint, which can be found in the same location.

  • After configuring OpenSWAN, restart the daemon on each endpoint and your tunnels should be established after a minute or two.

OpenBSD

Tested on OpenBSD 5.0 (updated on 2012-02-25).

  • Setting up IPsec on OpenBSD is a fairly straightforward task due to improvements in recent releases. Enabling it is as simple as changing the following in your /etc/rc.conf:
isakmpd_flags="-K"
ipsec=YES
  • Configure /etc/ipsec.conf on vpn1:
ike esp from 2001:db8:1::/64 to 2001:db8:2::/64 \
    peer vpn2.example.com \
    main auth hmac-sha2-256 enc aes-256 group modp2048 \
    quick auth hmac-sha2-256 enc aes-256 group modp2048 \
    srcid vpn1.example.com tag ipsec-vpn1
  • Configure /etc/ipsec.conf on vpn2:
ike esp from 2001:db8:2::/64 to 2001:db8:1::/64 \
    peer vpn1.example.com \
    main auth hmac-sha2-256 enc aes-256 group modp2048 \
    quick auth hmac-sha2-256 enc aes-256 group modp2048 \
    srcid vpn2.example.com tag ipsec-vpn1
  • We will be using RSA public key authentication, similar to what is commonly done with SSH, here. When you installed OpenBSD, the file /etc/isakmpd/local.pub was generated. This file will need to be copied to the other endpoint and vice versa. To set this up on vpn1, simply copy /etc/isakmpd/local.pub on vpn1 to /etc/isakmpd/pubkeys/fqdn/vpn1.example.com on vpn2. Next do this process in reverse for vpn2.
  • After you make the necessary changes, starting IPsec is simply a matter of running the following command on each endpoint to start your tunnels:
sudo /etc/rc.d/isakmpd start
sudo ipsecctl -f /etc/ipsec.conf

The changes we made to rc.conf above ensure that your IPsec tunnels will be reestablished on boot.

Roadwarrior

Linux with OpenSWAN

Tested with OpenSWAN 2.6.41 on Arch Linux (updated on 2014-09-12).

  • Generate a new host key on both endpoints:
sudo ipsec newhostkey --output /etc/ipsec.secrets
  • Configure /etc/ipsec.conf on your VPN server:
config setup
    protostack=netkey
    nat_traversal=on

conn myvpn
    authby=rsasig
    connaddrfamily=ipv6
    type=tunnel

    ike=aes256-sha2_256;modp2048
    phase2alg=aes256-sha2_256;modp2048
    sha2_truncbug=yes

    left=vpn1.example.com
    leftid=@vpn1.example.com
    leftsubnet=2001:db8:1::/64
    leftrsasigkey=0s...

    right=%any
    rightid=@vpn2.example.com
    rightsubnet=2001:db8:2::/64
    rightrsasigkey=0s...

    auto=start

Make sure to change leftrsasigkey to the public key of the RSA key that was generated in the above command, which can be found in /etc/ipsec.secrets. Replace rightrsasigkey with the RSA generated by the above command on the other endpoint, which can be found in the same location.

  • Configure /etc/ipsec.conf on the machine that will connect to your VPN:
config setup
    protostack=netkey
    nat_traversal=on

conn vpn1
    authby=rsasig
    connaddrfamily=ipv6
    type=tunnel

    ike=aes256-sha2_256;modp2048
    phase2alg=aes256-sha2_256;modp2048
    sha2_truncbug=yes

    left=%defaultroute
    leftid=@vpn2.example.com
    leftsubnet=2001:db8:2::1/128
    leftsourceip=2001:db8:2::1
    leftrsasigkey=0s...

    right=vpn1.example.com
    rightid=@vpn1.example.com
    rightsubnet=2001:db8:1::/64
    rightrsasigkey=0s...

    auto=start

Make sure to change leftrsasigkey to the public key of the RSA key that was generated in the above command, which can be found in /etc/ipsec.secrets. Replace rightrsasigkey with the RSA generated by the above command on the other endpoint, which can be found in the same location.

  • After configuring OpenSWAN, restart the daemon on each endpoint and your tunnels should be established after a minute or two.

OpenBSD

Tested on OpenBSD 5.1 (updated on 2012-06-27).

  • Setting up IPsec on OpenBSD is a fairly straightforward task due to improvements in recent releases. Enabling it is as simple as changing the following in your /etc/rc.conf:
isakmpd_flags="-K"
ipsec=YES
  • Configure /etc/ipsec.conf on your VPN server:
ike esp from 2001:db8:1::/64 to 2001:db8:2::1 \
    peer any \
    main auth hmac-sha2-256 enc aes-256 group modp2048 \
    quick auth hmac-sha2-256 enc aes-256 group modp2048 \
    srcid vpn1.example.com tag ipsec-vpn1
  • Configure /etc/ipsec.conf on the machine that will connect to your VPN:
ike esp from 2001:db8:2::1 to 2001:db8:1::/64 \
    peer vpn1.example.com \
    main auth hmac-sha2-256 enc aes-256 group modp2048 \
    quick auth hmac-sha2-256 enc aes-256 group modp2048 \
    srcid vpn2.example.com tag ipsec-vpn1
  • We will be using RSA public key authentication, similar to what is commonly done with SSH, here. When you installed OpenBSD, the file /etc/isakmpd/local.pub was generated. This file will need to be copied to the other endpoint and vice versa. To set this up on vpn1, simply copy /etc/isakmpd/local.pub on vpn1 to /etc/isakmpd/pubkeys/fqdn/vpn1.example.com on vpn2. Next do this process in reverse for vpn2.
  • After you make the necessary changes, starting IPsec is simply a matter of running the following command on each endpoint to start your tunnels:
sudo /etc/rc.d/isakmpd start
sudo ipsecctl -f /etc/ipsec.conf

The changes we made to rc.conf above ensure that your IPsec tunnels will be reestablished on boot.

Linux with OpenSWAN (laptop) to OpenBSD (router)

Tested on OpenBSD 5.1 (updated on 2012-06-27).

Assume router has an IPv4 only hostname of home.example.org and you want to route the IPv6 subnet 2001:420:1:9A8::/64 Assume the laptop is called laptop.example.org (does not have to be an actuall DNS entry) and will round the org-local subnet fd20:50::1/128 (which is actually just 1 ip)

  • Setting up IPsec on OpenBSD is a fairly straightforward task due to improvements in recent releases. Enabling it is as simple as changing the following in your /etc/rc.conf:
isakmpd_flags="-K"
ipsec=YES
  • Configure /etc/ipsec.conf on home.example.org:
ike esp from 2001:420:1:9A8::/64 to fd20:50::1/128 \
    peer any \
    main auth hmac-sha2-256 enc aes-256 group modp2048 \
    quick auth hmac-sha2-256 enc aes-256 group modp2048 \
    srcid home.example.org tag ipsec-vpn1
  • Generate a new host key on laptop.example.org:
sudo ipsec newhostkey --output /etc/ipsec.secrets
  • Configure /etc/ipsec.conf on laptop.example.org:
config setup
    protostack=netkey
    nat_traversal=off

conn vpn2
  authby=rsasig
  connaddrfamily=ipv6
  type=tunnel

  ike=aes256-sha2_256;modp2048
  phase2alg=aes256-sha2_256;modp2048
  sha2_truncbug=yes

  left=%defaultroute
  leftid=@laptop.example.org
  leftsubnet=fd20:50::1/128
  leftsourceip=fd20:50::1
  leftrsasigkey=<laptop_pubkey> # from /etc/ipsec.secrets on laptop.example.org

  right=home.example.org
  rightid=@home.example.org
  rightsubnet=2001:420:1:9A8::/64
  rightrsasigkey=<server_pubkey> # converted later from key on home.example.org

  auto=start

The trickiest part (and its not actually *that* tricky) is to convert the the pubkey on Linux to the format OpenBSD uses, and vice versa. There is a handy perl script found here that takes in a Linux or OpenBSD formated pubkey in stdin and outputs a OpenBSD or Linux formated pubkey.

On OpenBSD the pubkey is found in /etc/isakmpd/local.pub and in Linux it is found in /etc/ipsec.secrets. In ipsec.secrets, you will find a public key like: 

#pubkey=0s...
  • To convert this to OpenBSD format, run
echo ": PUB 0s..." | ./ipsec.pl

where 0s... is your full public key.

  • For the OpenBSD key, it is possible to pipe in local.pub like:
cat local.pub | ./ipsec.pl
  • Place the output from the OpenBSD pubkey into /etc/ipsec.conf on laptop.example.org here:
rightrsasigkey=<server_pubkey>

and put the output for the Linux pubkey into /etc/isakmpd/pubkeys/fqdn/laptop.example.org

  • After you make the necessary changes, starting IPsec is simply a matter of running the following command on home.example.org:
sudo /etc/rc.d/isakmpd start
sudo ipsecctl -f /etc/ipsec.conf

and on laptop.example.org restart openswan (generally under the rc script name ipsec) in whatever manner perscribed by your favorite distro.

Linux with strongSwan (laptop) to OpenBSD (router)

Tested on OpenBSD 5.5 and Arch Linux (updated on 2014-10-05).

Assume your router has the hostname home.example.org and you want to route the IPv6 subnet 2001:db8:1::/64 from your laptop, laptop.example.org. Note that DNS entries are not required for either of these. We will be using IKEv1 for key exchange, as IKEv2 support on OpenBSD was not complete at the time of writing.

  • Setting up IPsec on OpenBSD is a fairly straightforward task due to improvements in recent releases. Enabling it is as simple as changing the following in your /etc/rc.conf:
isakmpd_flags="-K"
ipsec=YES
  • Configure /etc/ipsec.conf on home.example.org:
ike passive esp from 2001:db8:1::/64 to any \
    peer any \
    main auth hmac-sha2-256 enc aes-256 group modp2048 \
    quick auth hmac-sha2-256 enc aes-256 group modp2048 \
    srcid home.example.org tag ipsec-vpn1
  • Generate a new host key on laptop.example.org:
sudo openssl genrsa -out /etc/ipsec.d/private/laptop.example.org.pem 4096
  • Add the path to that private key you generated to /etc/ipsec.secrets:
: RSA home.example.org.pem
  • Extract the corresponding public key for your private key:
sudo openssl rsa -in /etc/ipsec.d/private/laptop.example.org.pem -pubout -out /etc/ipsec.d/certs/laptop.example.org.pem
  • Configure /etc/ipsec.conf on laptop.example.org:
config setup

conn home
    keyexchange=ikev1
    authby=pubkey
    connaddrfamily=ipv6
    type=tunnel

    ike=aes256-sha256-modp2048
    esp=aes256-sha256-modp2048

    left=%defaultroute
    leftid=@laptop.example.org
    leftsubnet=fdf0:f00::1/128
    leftrsasigkey=laptop.example.org.pem

    # if you don't have home.example.org in DNS or don't want strongswan to do a DNS lookup when it starts, hardcode the right IP
    right=home.example.org
    rightid=@home.example.org
    rightsubnet=2001:db8:1::/64
    rightrsasigkey=home.example.org.pem

    auto=add

Note that leftsubnet should correspond to the IPv6 source address you want to use. You will need to manually configure this address on your interface, and add a route for traffic to rightsubnet, if one does not exist already.

  • Copy the /etc/ipsec.d/certs/home.example.org.pem from laptop.example.org and place it at /etc/isakmpd/pubkeys/fqdn/home.example.org on home.example.org.
  • Download the /etc/isakmpd/local.pub file from home.example.org and place it at /etc/ipsec.d/certs/home.example.org.pem.
  • After you make the necessary changes, starting IPsec is simply a matter of running the following command on home.example.org:
sudo /etc/rc.d/isakmpd start
sudo ipsecctl -f /etc/ipsec.conf

and on laptop.example.org, restart strongswan: 

sudo systemctl restart strongswan.service

External links

Retrieved from "https://vtluug.org/w/index.php?title=IPsec&oldid=7396"