OpenVPN : Configure VPN Server2024/09/23

Install OpenVPN to Configure Virtual Private Network.

This example is based on the environment like follows.
By settings of OpenVPN Server/Client, [tun] interface will be configured automatically and when connecting with VPN from Client to Server, Client can access to the the local network of the Server.

On this example, it needs to set IP Masquerading on Router, too.

  +----------------------+
  | [  OpenVPN Server  ] |172.16.100.1
  |    dlp.srv.world     +--------+
  |                      |tun     |
  +-----------+----------+        |
        vtnet0|10.0.0.30          |
              |                   |
              |  Local Network    |
      10.0.0.1|                   |
       +------+-----+             |
-------|   Router   |-------------|-----
       +------+-----+             |
              |                   |
              |  Internet         |
--------------+-------------------|-----
              |                   |
              |  Local Network    |
  192.168.0.30|                   |
  +-----------+----------+        |
  |                      |tun     |
  |      VPN Client      +--------+
  |                      |172.16.100.x
  +----------------------+

[1]	Install OpenVPN.

root@dlp:~ #

pkg install -y openvpn easy-rsa

[2]	Create CA and Certificates.

root@dlp:~ #

easyrsa init-pki


Notice
------
'init-pki' complete; you may now create a CA or requests.

Your newly created PKI dir is:
* /root/pki

Using Easy-RSA configuration:
* undefined

# create CA

root@dlp:~ #

easyrsa build-ca

No Easy-RSA 'vars' configuration file exists!

Using SSL:
* openssl OpenSSL 3.0.13 30 Jan 2024 (Library: OpenSSL 3.0.13 30 Jan 2024)

# set any pass-phrase
Enter New CA Key Passphrase:
Re-Enter New CA Key Passphrase:
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Common Name (eg: your user, host, or server name) [Easy-RSA CA]:Server-CA

Notice
------
CA creation complete. Your new CA certificate is at:
* /root/pki/ca.crt

# create server certificates
# any name is OK for [server1] name
# (it is set for file name of certs or commonName)

root@dlp:~ #

easyrsa build-server-full server1 nopass

No Easy-RSA 'vars' configuration file exists!

Using SSL:
* openssl OpenSSL 3.0.13 30 Jan 2024 (Library: OpenSSL 3.0.13 30 Jan 2024)

.....
.....

Notice
------
Private-Key and Public-Certificate-Request files created.
Your files are:
* req: /root/pki/reqs/server1.req
* key: /root/pki/private/server1.key

You are about to sign the following certificate:
Request subject, to be signed as a server certificate
for '825' days:

subject=
    commonName                = server1

Type the word 'yes' to continue, or any other input to abort.
  Confirm request details: yes

Using configuration from /root/pki/openssl-easyrsa.cnf
# answer with pass-phrase set on CA
Enter pass phrase for /root/pki/private/ca.key:
Check that the request matches the signature
Signature ok
The Subject's Distinguished Name is as follows
commonName            :ASN.1 12:'server1'
Certificate is to be certified until Dec 27 00:25:48 2026 GMT (825 days)

Write out database with 1 new entries
Database updated

Notice
------
Certificate created at:
* /root/pki/issued/server1.crt

Notice
------
Inline file created:
* /root/pki/inline/server1.inline

# create client certificates
# any name is OK for [client1] name
# (it is set for file name of certs or commonName)

root@dlp:~ #

easyrsa build-client-full client1 nopass

No Easy-RSA 'vars' configuration file exists!

Using SSL:
* openssl OpenSSL 3.0.13 30 Jan 2024 (Library: OpenSSL 3.0.13 30 Jan 2024)

.....
.....

Notice
------
Private-Key and Public-Certificate-Request files created.
Your files are:
* req: /root/pki/reqs/client1.req
* key: /root/pki/private/client1.key

You are about to sign the following certificate:
Request subject, to be signed as a client certificate
for '825' days:

subject=
    commonName                = client1

Type the word 'yes' to continue, or any other input to abort.
  Confirm request details: yes

Using configuration from /root/pki/openssl-easyrsa.cnf
# answer with pass-phrase set on CA
Enter pass phrase for /root/pki/private/ca.key:
Check that the request matches the signature
Signature ok
The Subject's Distinguished Name is as follows
commonName            :ASN.1 12:'client1'
Certificate is to be certified until Dec 27 00:27:59 2026 GMT (825 days)

Write out database with 1 new entries
Database updated

Notice
------
Certificate created at:
* /root/pki/issued/client1.crt

Notice
------
Inline file created:
* /root/pki/inline/client1.inline

# generate Diffie Hellman ( DH ) parameter

root@dlp:~ #

easyrsa gen-dh

No Easy-RSA 'vars' configuration file exists!

Using SSL:
* openssl OpenSSL 3.0.13 30 Jan 2024 (Library: OpenSSL 3.0.13 30 Jan 2024)
Generating DH parameters, 2048 bit long safe prime

.....
.....

DH parameters appear to be ok.

Notice
------

DH parameters of size 2048 created at:
* /root/pki/dh.pem

# create TLS-Auth key

root@dlp:~ #

openvpn --genkey secret ./pki/ta.key

# copy generated certs

root@dlp:~ #

mkdir /usr/local/etc/openvpn

root@dlp:~ #

cp -pR ./pki/issued /usr/local/etc/openvpn/

root@dlp:~ #

cp -pR ./pki/private /usr/local/etc/openvpn/

root@dlp:~ #

cp -pR ./pki/ca.crt /usr/local/etc/openvpn/

root@dlp:~ #

cp -pR ./pki/dh.pem /usr/local/etc/openvpn/

root@dlp:~ #

cp -pR ./pki/ta.key /usr/local/etc/openvpn/

[3]	Configure OpenVPN.

# copy sample configuration

root@dlp:~ #

cp /usr/local/share/examples/openvpn/sample-config-files/server.conf /usr/local/etc/openvpn/openvpn.conf

root@dlp:~ #

vi /usr/local/etc/openvpn/openvpn.conf

# line 32 : change if need (listening port of OpenVPN)

port 1194

# line 35 : change if need (use udp on this example)

;proto tcp
proto udp

# line 53 : change if need (use tun on this example)

;dev tap
dev tun

# line 86 : specify certificates

ca.crt

cert

issued/server1.crt

key

private/server1.key

# line 93 : specify DH file

dh.pem

# line 115 : specify network to be used on VPN
# any network are OK except your local network

server

172.16.100.0 255.255.255.0

# line 156 : uncomment and change to your local network

push "route

10.0.0.0 255.255.255.0

# line 245 : keepalive settings

keepalive 10 120

# line 258 : uncomment and specify TLS-Auth key

tls-auth

ta.key 0

# line 276 : enable persist options

persist-key
persist-tun

# line 301 : specify log level (0 - 9, 9 means debug level)

verb 3

root@dlp:~ #

service openvpn enable

openvpn enabled in /etc/rc.conf
root@dlp:~ #

service openvpn start

Starting openvpn.

[4]	Transfer certificates below to VPN client host. * /usr/local/etc/openvpn/ca.crt * /usr/local/etc/openvpn/ta.key * /usr/local/etc/openvpn/issued/client1.crt * /usr/local/etc/openvpn/private/client1.key

[5]	Configure packet filters to allow VPN clients to access to local network.

root@dlp:~ #

sysctl net.inet.ip.forwarding=1

net.inet.ip.forwarding: 0 -> 1
root@dlp:~ #

echo 'net.inet.ip.forwarding=1' >> /etc/sysctl.conf

root@dlp:~ #

vi /etc/pf.conf

# create new

ext_if = "vtnet0"
wg_net = "172.16.100.0/24"
set skip on lo
scrub in on $ext_if all fragment reassemble
nat on $ext_if from $wg_net to any -> ($ext_if)

root@dlp:~ #

service pflog enable

pflog enabled in /etc/rc.conf
root@dlp:~ #

service pf enable

pf enabled in /etc/rc.conf
root@dlp:~ #

service pf start

root@dlp:~ #

service pflog start

# if your openvpn server is running on virtual machine, disable checksum offload

root@dlp:~ #

ifconfig vtnet0 -rxcsum -txcsum -rxcsum6 -txcsum6 -tso -lro

root@dlp:~ #

echo "ifconfig vtnet0 -rxcsum -txcsum -rxcsum6 -txcsum6 -tso -lro" >> /etc/rc.conf

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