Installing and configuring OpenVPN server in CentOS 5.4

First assuming you already had rpmforge yum repos.
Just need to get open rpm installed..

 yum install openvpn -y

Now start configure it :
get into the OpenVPN configuration folder

  cd /etc/openvpn/

Generate the secret key at the server ..
(this file shall be transferred to each client too..)

 openvpn --genkey --secret ta.key

Now get the rest of cert and generate appropriate keys/pair.
The tools are provided under the following directory

  cd /usr/share/doc/openvpn-2.0.9/easy-rsa/

make all the script there it executable ..

  chmod a+x *

Prepare the output keys folder

  mkdir keys
  ./vars

Clean it up..

 ./clean-all

Start building server key first ..

 ./build-ca
./build-key-server home.namran.net

Okay .. now try to add a client cert to it..

 ./build-key nbnamran

Some encryption/decipher thing..

 ./build-dh

Now copied the generated keys/cert into openvpn configuration folder.

  cp /usr/share/doc/openvpn-2.0.9/easy-rsa/keys/* /etc/openvpn/

Time to config the configuration file ..

[ad#postad]

  cd /etc/openvpn

Let’s just copy from sample first ..

 cp /usr/share/doc/openvpn-2.0.9/sample-config-files/server.conf .

Edit it ..

   vi server.conf

.. so that it become something like this :

diff -up /usr/share/doc/openvpn-2.0.9/sample-config-files/server.conf /etc/openvpn/server.conf 
--- /usr/share/doc/openvpn-2.0.9/sample-config-files/server.conf        2006-01-07 05:49:27.000000000 +0800
+++ /etc/openvpn/server.conf    2010-02-01 21:10:48.000000000 +0800
@@ -32,8 +32,8 @@
 port 1194
 
 # TCP or UDP server?
-;proto tcp
-proto udp
+proto tcp
+;proto udp
 
 # "dev tun" will create a routed IP tunnel,
 # "dev tap" will create an ethernet tunnel.
@@ -75,16 +75,16 @@ dev tun
 # Any X509 key management system can be used.
 # OpenVPN can also use a PKCS #12 formatted key file
 # (see "pkcs12" directive in man page).
-ca ca.crt
-cert server.crt
-key server.key  # This file should be kept secret
+ca /etc/openvpn/ca.crt
+cert /etc/openvpn/home.namran.net.crt
+key /etc/openvpn/home.namran.net.key  # This file should be kept secret
 
 # Diffie hellman parameters.
 # Generate your own with:
 #   openssl dhparam -out dh1024.pem 1024
 # Substitute 2048 for 1024 if you are using
 # 2048 bit keys. 
-dh dh1024.pem
+dh /etc/openvpn/dh1024.pem
 
 # Configure server mode and supply a VPN subnet
 # for OpenVPN to draw client addresses from.
@@ -93,14 +93,14 @@ dh dh1024.pem
 # Each client will be able to reach the server
 # on 10.8.0.1. Comment this line out if you are
 # ethernet bridging. See the man page for more info.
-server 10.8.0.0 255.255.255.0
+server 192.168.144.0 255.255.255.0
 
 # Maintain a record of client <-> virtual IP address
 # associations in this file.  If OpenVPN goes down or
 # is restarted, reconnecting clients can be assigned
 # the same virtual IP address from the pool that was
 # previously assigned.
-ifconfig-pool-persist ipp.txt
+ifconfig-pool-persist /etc/openvpn/ipp.txt
 
 # Configure server mode for ethernet bridging.
 # You must first use your OS's bridging capability
@@ -121,7 +121,7 @@ ifconfig-pool-persist ipp.txt
 # to know to route the OpenVPN client
 # address pool (10.8.0.0/255.255.255.0)
 # back to the OpenVPN server.
-;push "route 192.168.10.0 255.255.255.0"
+push "route 192.168.133.0 255.255.255.0"
 ;push "route 192.168.20.0 255.255.255.0"
 
 # To assign specific IP addresses to specific
@@ -193,7 +193,7 @@ ifconfig-pool-persist ipp.txt
 # To force clients to only see the server, you
 # will also need to appropriately firewall the
 # server's TUN/TAP interface.
-;client-to-client
+client-to-client
 
 # Uncomment this directive if multiple clients
 # might connect with the same certificate/key
@@ -206,7 +206,7 @@ ifconfig-pool-persist ipp.txt
 # CERTIFICATE/KEY PAIRS FOR EACH CLIENT,
 # EACH HAVING ITS OWN UNIQUE "COMMON NAME",
 # UNCOMMENT THIS LINE OUT.
-;duplicate-cn
+duplicate-cn
 
 # The keepalive directive causes ping-like
 # messages to be sent back and forth over
@@ -228,7 +228,7 @@ keepalive 10 120
 # a copy of this key.
 # The second parameter should be '0'
 # on the server and '1' on the clients.
-;tls-auth ta.key 0 # This file is secret
+tls-auth /etc/openvpn/ta.key 0 # This file is secret
 
 # Select a cryptographic cipher.
 # This config item must be copied to
@@ -251,8 +251,8 @@ comp-lzo
 #
 # You can uncomment this out on
 # non-Windows systems.
-;user nobody
-;group nobody
+user nobody
+group nobody
 
 # The persist options will try to avoid
 # accessing certain resources on restart
@@ -264,7 +264,7 @@ persist-tun
 # Output a short status file showing
 # current connections, truncated
 # and rewritten every minute.
-status openvpn-status.log
+status /var/log/openvpn-status.log
 
 # By default, log messages will go to the syslog (or
 # on Windows, if running as a service, they will go to

Start the openvpn server services :

  service openvpn start

setup the client and then Monitor the incoming connection..

 tail -f /var/log/messages

… ops.. firewall might need to open the port accordingly first!

  vi /etc/arno-iptables-firewall/firewall.conf
  /etc/init.d/arno-iptables-firewall restart

.. the client preparation is as below :

  cp /usr/share/doc/openvpn-2.0.9/easy-rsa/keys/nbnamran.* /home/namran/Desktop/vpn
  cp /usr/share/doc/openvpn-2.0.9/easy-rsa/keys/ca.crt /home/namran/Desktop/vpn
 
 
  cp /etc/openvpn/ta.key /home/namran/Desktop/vpn
  chown namran:namran /home/namran/Desktop/vpn/nbnamran.*
  chown namran:namran /home/namran/Desktop/vpn/ta.key
[namran@nb-namran openvpn]$ cat client.ovpn 
##############################################
# Sample client-side OpenVPN 2.0 config file #
# for connecting to multi-client server.     #
#                                            #
# This configuration can be used by multiple #
# clients, however each client should have   #
# its own cert and key files.                #
#                                            #
# On Windows, you might want to rename this  #
# file so it has a .ovpn extension           #
##############################################
 
# Specify that we are a client and that we
# will be pulling certain config file directives
# from the server.
client
 
# Use the same setting as you are using on
# the server.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap
dev tun
 
# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel
# if you have more than one.  On XP SP2,
# you may need to disable the firewall
# for the TAP adapter.
;dev-node MyTap
 
# Are we connecting to a TCP or
# UDP server?  Use the same setting as
# on the server.
proto tcp
;proto udp
 
# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
remote home.namran.net 1194
;remote my-server-2 1194
 
# Choose a random host from the remote
# list for load-balancing.  Otherwise
# try hosts in the order specified.
;remote-random
 
# Keep trying indefinitely to resolve the
# host name of the OpenVPN server.  Very useful
# on machines which are not permanently connected
# to the internet such as laptops.
resolv-retry infinite
 
# Most clients don't need to bind to
# a specific local port number.
nobind
 
# Downgrade privileges after initialization (non-Windows only)
;user nobody
;group nobody
 
# Try to preserve some state across restarts.
persist-key
persist-tun
 
# If you are connecting through an
# HTTP proxy to reach the actual OpenVPN
# server, put the proxy server/IP and
# port number here.  See the man page
# if your proxy server requires
# authentication.
;http-proxy-retry # retry on connection failures
;http-proxy [proxy server] [proxy port #]
 
# Wireless networks often produce a lot
# of duplicate packets.  Set this flag
# to silence duplicate packet warnings.
;mute-replay-warnings
 
# SSL/TLS parms.
# See the server config file for more
# description.  It's best to use
# a separate .crt/.key file pair
# for each client.  A single ca
# file can be used for all clients.
ca ca.crt
cert nbnamran.crt
key nbnamran.key
 
# Verify server certificate by checking
# that the certicate has the nsCertType
# field set to "server".  This is an
# important precaution to protect against
# a potential attack discussed here:
#  http://openvpn.net/howto.html#mitm
#
# To use this feature, you will need to generate
# your server certificates with the nsCertType
# field set to "server".  The build-key-server
# script in the easy-rsa folder will do this.
ns-cert-type server
 
# If a tls-auth key is used on the server
# then every client must also have the key.
tls-auth ta.key 1
 
# Select a cryptographic cipher.
# If the cipher option is used on the server
# then you must also specify it here.
;cipher x
 
# Enable compression on the VPN link.
# Don't enable this unless it is also
# enabled in the server config file.
comp-lzo
 
# Set log file verbosity.
verb 3
 
# Silence repeating messages
;mute 20

and the files needed for the client is as below :

[namran@nb-namran openvpn]$ ls
ca.crt  client.ovpn  nbnamran.crt  nbnamran.csr  nbnamran.key  ta.key

.. that’s it.!

p/s : .. pretty nice as it also work on windows machine…
only the part of cert would make it a bit difficult to connect from other native device such as handphone!
.. if someone happen to hack the way for IPSec on this.. kindly leave your note below .. hehe..

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