Introduction

Here be dragons. This section should cover the basics:

IKEv1
Three stages: Key distribution, IPSec setup, GRE setup
In theory, BGPd can set up IPSec flows itself, but we're not using that here because that prevents you from using another BGP daemon such as bird
Debugging

Key generation and distribution

Using pre-generated keys

OpenBSD generates keys suitables for IPSec usage during the installation. The public key can be found in /etc/isakmpd/local.pub

Generating your own keys

If you don't want to use a pre-generated key, refer to isakmpd(8).

Distributing keys

Send your public key to your peer, preferrably digitally signed. A signature can be created with gpg -sb -a local.pub and checked with gpg --verify local.pub.asc. Since the key is not private, it can be transmitted in the open and on a public forum, such as a Pastebin service.

Once your peer sent you their public key, it under /etc/isakmpd/pubkeys/fqdn, /etc/isakmpd/pubkeys/ipv4 or /etc/isakmpd/ipv6, depending on the ID type the peer is using. The key file should be named after the peers ID. For example, if your peer is 1.3.3.7, you place their public key under /etc/isakmpd/pubkeys/ipv4/1.3.3.7.

If your peers public key is not in PEM format, you can use pubkey-converter to convert between key formats.

IPSec Setup

Change the value of the isakmpd_flags variable in /etc/rc.conf.local to "-K", or add the "-K" flag if you already have flags in there.

Next, add the right flow parameters to /etc/ipsec.conf. We are using the following parameters in this example:

Encryption: AES-128
Authentication hash: HMAC-SHA1
DH Group: modp1536
Phase 1 lifetime: 28800 seconds
Phase 2 lifetime: 3600 seconds
Peer address: 1.3.3.7
Local address: 3.4.5.6

The configuration file should look like this:

mymachine = "3.4.5.6"
mypeer    = "1.3.3.7"
ike esp transport proto gre from $mymachine to $mypeer \
  main auth hmac-sha1 enc aes-128 group modp1536 lifetime 28800 \
  quick auth hmac-sha1 enc aes-128 group modp1536 lifetime 3600

Load the configuration file into isakmpd: ipsecctl -f /etc/ipsec.conf. Once the connection is established, the IPSec flows can be listed with ipsecctl -sa:

# ipsecctl -sa
FLOWS:
flow esp in proto gre from 1.3.3.7 to 3.4.5.6 peer 1.3.3.7 srcid 3.4.5.6/32 dstid 1.3.3.7/32 type use
flow esp out proto gre from 3.4.5.6 to 1.3.3.7 peer 1.3.3.7 srcid 3.4.5.6/32 dstid 1.3.3.7/32 type require

SAD:
esp transport from 1.3.3.7 to 3.4.5.6 spi 0xdeadbeef auth hmac-sha1 enc aes
esp transport from 3.4.5.6 to 1.3.3.7 spi 0xf00df00d auth hmac-sha1 enc aes

GRE Setup

Next, we will set up the GRE device. The gre(4) device encapsulates IPv4 and IPv6 traffic, which allows you to speak both address families over one tunnel if you only have native connectivity for one address family. The addresses configured onto the GRE device should come from a private address range that is not used anywhere in DN42, or a registered transfer net. For IPv6, you should use either ULAs or Link-Local addresses. In this example, we assume you are using 10.20.30.0/31 as the IPv4 transfer "net" (it has only two addresses, so calling it a network is a bit of an overstatement) and Link-Local addresses for IPv6.

# ifconfig gre0 tunnel 3.4.5.6 1.3.3.7
# ifconfig gre0 inet 10.20.30.0 10.20.30.1 # reverse these on your peer's side
# ifconfig gre0 inet6 eui64

These settings should also be added to /etc/hostname.gre0, .i.e.

tunnel 3.4.5.6 1.3.3.7
inet 10.20.30.0 10.20.30.1
inet6 eui64