2020-09-12: Configuring OpenIKED VPNs for Road Warriors       rak
=================================================================

A few weeks ago I configured a road warrior VPN setup. The
remote end is on a VPS running OpenBSD and OpenIKED, the VPN is
an IKEv2 VPN using x509 authentication, and the local end is
StrongSwan. I also configured an IKEv2 VPN between my VPSs. Here
are the notes for how to do so.

In all cases, to use x509 authentication, you will need to
generate a bunch of certificates and keys:

* a CA certificate
* a key/certificate pair for each client

Fortunately, OpenIKED provides the ikectl utility to help you do
so. Before going any further, you might find it useful to edit
/etc/ssl/ikeca.cnf to set some reasonable defaults for your
certificates.

Begin by creating and installing a CA certificate:

# ikectl ca vpn create
# ikectl ca vpn install

For simplicity, I am going to assume that the you are managing
your CA on the same host as one of the hosts that you want to
configure for the VPN. If not, see the bit about exporting
certificates at the beginning of the section on persistent
host-host VPNs.

Create and install a key/certificate pair for your server.
Suppose for example your first server is called
server1.example.org:

# ikectl ca vpn certificate server1.example.org create
# ikectl ca vpn certificate server1.example.org install


## Persistent host-host VPNs

For each other server that you want to use, you need to also
create a key/certificate pair on the same host as the CA
certificate, and then copy them over to the other server.
Assuming the other server is called server2.example.org:

# ikectl ca vpn certificate server2.example.org create
# ikectl ca vpn certificate server2.example.org export

This last command will produce a tarball
server2.example.org.tgz. Copy it over to server2.example.org and
install it:

# tar -C /etc/iked -xzpvf server2.example.org.tgz

Next, it is time to configure iked. To do so, you will need to
find some information about the certificates you just generated.
On the host with the CA, run

$ cat /etc/ssl/vpn/index.txt
V       210825142056Z           01      unknown /C=US/ST=Pennsylvania/L=Pittsburgh/CN=server1.example.org/[email protected]
V       210825142208Z           02      unknown /C=US/ST=Pennsylvania/L=Pittsburgh/CN=server2.example.org/[email protected]

Pick one of the two hosts to play the "active" role (in this
case, server1.example.org). Using the information you gleaned
from index.txt, add the following to /etc/iked.conf, filling in
the srcid and dstid fields appropriately.

ikev2 'server1_server2_active' active esp from server1.example.org to server2.example.org \
       local server1.example.org peer server2.example.org \
       srcid '/C=US/ST=Pennsylvania/L=Pittsburgh/CN=server1.example.org/[email protected]' \
       dstid '/C=US/ST=Pennsylvania/L=Pittsburgh/CN=server2.example.org/[email protected]'

On the other host, add the following to /etc/iked.conf

ikev2 'server2_server1_passive' passive esp from server2.example.org to server1.example.org \
       local server2.example.org peer server1.example.org \
       srcid '/C=US/ST=Pennsylvania/L=Pittsburgh/CN=server2.example.org/[email protected]' \
       dstid '/C=US/ST=Pennsylvania/L=Pittsburgh/CN=server1.example.org/[email protected]'

Note that the names 'server1_server2_active' and
'server2_server1_passive' in the two stanzas do not matter and
can be omitted. Reload iked on both hosts:

# ikectl reload

If everything worked out, you should see the negotiated security
associations (SAs) in the output of

# ikectl show sa

On OpenBSD, you should also see some output on success or errors
in the file /var/log/daemon.



## For a road warrior

Add the following to /etc/iked.conf on the remote end:

ikev2 'responder_x509' passive esp \
       from 0.0.0.0/0 to 10.0.1.0/24 \
       local server1.example.org peer any \
       srcid server1.example.org \
       config address 10.0.1.0/24 \
       config name-server 10.0.1.1 \
       tag "ROADW"

Configure or omit the address range and the name-server
configurations to suit your needs. See iked.conf(5) for details.
Reload iked:

# ikectl reload

If you are on OpenBSD and want the remote end to have an IP
address, add the following to /etc/hostname.vether0, again
configuring the address to suit your needs:

inet 10.0.1.1 255.255.255.0

Put the interface up:

# ifconfig vether0 up

Now create a client certificate for authentication. In my case,
my road-warrior client was client.example.org:

# ikectl ca vpn certificate client.example.org create
# ikectl ca vpn certificate client.example.org export

Copy client.example.org.tgz to client and run

# tar -C /etc/ipsec.d/ -xzf client.example.org.tgz -- \
       ./private/client.example.org.key \
       ./certs/client.example.org.crt ./ca/ca.crt

Install StrongSwan and add the following to /etc/ipsec.conf,
configuring appropriately:

ca example.org
 cacert=ca.crt
 auto=add

conn server1
 keyexchange=ikev2
 right=server1.example.org
 rightid=%server1.example.org
 rightsubnet=0.0.0.0/0
 rightauth=pubkey
 leftsourceip=%config
 leftauth=pubkey
 leftcert=client.example.org.crt
 auto=route

Add the following to /etc/ipsec.secrets:

# space is important
server1.example.org : RSA client.example.org.key

Restart StrongSwan, put the connection up, and check its status:

# ipsec restart
# ipsec up server1
# ipsec status

That should be it.


Sources:

https://wiki.strongswan.org/projects/strongswan/wiki/IKEv2ClientConfig
https://www.openbsd.org/faq/faq17.html
ikectl(8)
iked.conf(5)

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