CentOS OpenVPN Server + Mikrotik OVPN client + Policy Based Routing guide.

Tested on CentOS 6.5 OpenVPN (as server) and MikroTik hAP lite (RB941-2nD-TC, smips 6.39.1) (as client).

Step 1. CentOS OpenVPN Server installation.

You already have server with installed CentOS 6.5. Let's install OpenVPN!

wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
rpm -Uvh epel-release-6-8.noarch.rpm
yum install openvpn easy-rsa

This method activates TLS/SSL encryption on the server, let's find our easy-rsa (/usr/share/easy-rsa):

cd /etc/openvpn
mkdir easy-rsa
cp -R /usr/share/easy-rsa/2.0/* easy-rsa/
chmod -R +x easy-rsa/

Initializing the script:

cd easy-rsa/
source ./vars
./clean-all

Create a CA certificate and key:

./build-ca

Create a certificate/key for the server:

./build-key-server server

Generating keys for encryption of SSL/TLS connections:

./build-dh

And create the keys for yourself:

./build-key client

Creating/deleting additional keys/certificates:

Creating additional OpenVPN keys/certificates:

cd /etc/openvpn/easy-rsa
source ./vars
./build-key your_new_key

Deleting OpenVPN keys/certificates:

cd /etc/openvpn/easy-rsa
source ./vars
./revoke-full sertificate_name

Then delete invalid certificates from '/etc/openvpn/easy-rsa/keys' and delete certs with marker 'I' from 'keys/index.txt':

cd /etc/openvpn/easy-rsa
source ./vars
nano keys/index.txt

Create and tune your openvpn.config:

cp /usr/share/doc/openvpn-2.3.2/sample/sample-config-files/server.conf /etc/openvpn

Edit your /etc/openvpn/server.conf:

local xxx.xxx.xxx.xxx #external ip of our vpn-server
port 1194
proto tcp
dev tun

ca  /etc/openvpn/easy-rsa/keys/ca.crt
cert    /etc/openvpn/easy-rsa/keys/server.crt
key     /etc/openvpn/easy-rsa/keys/server.key
dh  /etc/openvpn/easy-rsa/keys/dh2048.pem

server 10.0.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt

push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"
keepalive 10 120

user nobody
group nobody
persist-key
persist-tun
status /var/log/openvpn-status.log
log /var/log/openvpn.log
verb 3

Now you can start the OpenVPN service:

service openvpn start

Add openvpn service in autoload:

chkconfig openvpn on

Check if the device for the tunnel has appeared:

ifconfig tun0

Is assigned address and port for OpenVPN server?:

netstat -tupln

Edit the file /etc/sysctl.conf:

net.ipv4.ip_forward = 1

Loading kernel variables from updated sysctl.conf:

sysctl -p

Add rules into iptables /etc/sysconfig/iptables:

*nat
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [1:124]
:OUTPUT ACCEPT [1:124]
-A POSTROUTING -s 10.0.0.0/24 -o eth0 -j MASQUERADE #openvpn
COMMIT
*filter
:INPUT ACCEPT [126:10528]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [112:13370]
-A INPUT -i tun0 -j ACCEPT #openvpn
-A INPUT -p tcp -m tcp --dport 1194 -j ACCEPT #openvpn
COMMIT

Restart the service:

service iptables restart

That's all. Your OpenVPN server is ready! :) Please note, if your OpenVPN server assigns the same IP's for all OpenVPN clients you need to use different certificates for all your vpn clients (go to 'Creating/deleting additional keys/certificates' step from this guide). Also keep in mind, commonName and name in your clients keys must be uniqe. For instance: client1, client2, client3, etc.

---

Step 2. Mikrotik router as OpenVPN Client.

Mikrotik OVPN client installation.

Please, keep in mind:

• UDP is not supported
• LZO compression is not supported
• username/passwords are not mandatory

Let's go:

ssh admin@192.168.1.1

  MMMM    MMMM       KKK                          TTTTTTTTTTT      KKK
  MMM MMMM MMM  III  KKK  KKK  RRRRRR     OOOOOO      TTT     III  KKK  KKK
  MMM  MM  MMM  III  KKKKK     RRR  RRR  OOO  OOO     TTT     III  KKKKK
  MMM      MMM  III  KKK KKK   RRRRRR    OOO  OOO     TTT     III  KKK KKK
  MMM      MMM  III  KKK  KKK  RRR  RRR   OOOOOO      TTT     III  KKK  KKK

  MikroTik RouterOS 6.39.1 (c) 1999-2017       http://www.mikrotik.com/

[?]             Gives the list of available commands
command [?]     Gives help on the command and list of arguments

[Tab]           Completes the command/word. If the input is ambiguous,
                a second [Tab] gives possible options

/               Move up to base level
..              Move up one level
/command        Use command at the base level

Check your Mikrotik OS version

All the code in this repo is for version 6.39.1. If yours is older than that go ahead and upgrade it first.

system package update download

Import OpenVPN certificates

You'll need some files from your OpenVPN server or VPN provider, only 2 files are required: client.crt client.key. Upload and import these certificates to your Mikrotik.

scp client.crt admin@192.168.1.1:/
scp client.key admin@192.168.1.1:/
certificate import file-name=client.crt
certificate import file-name=client.key

You can check that it's worked:

certificate print

Flags: K - private-key, D - dsa, L - crl, C - smart-card-key, A - authority, I - issued, R - revoked, E - expired, T - trusted 
 #          NAME               COMMON-NAME        SUBJECT-ALT-NAME      FINGERPRINT              
 0 K      T client.crt_0       OpenVPN                                  12911f9e101be5b3e15cd...

Create an OpenVPN PPP profile

This section contains all the details of how you will connect to the server, the following worked for me.

ppp profile add name=OVPN-client change-tcp-mss=yes only-one=yes use-encryption=yes use-mpls=no use-compression=no

You can check that it's worked:

ppp profile print

Flags: * - default 
 0 * name="default" use-mpls=default use-compression=default use-encryption=default only-one=default change-tcp-mss=yes use-upnp=default 
     address-list="" on-up="" on-down="" 
 1   name="OVPN-client" use-mpls=no use-compression=no use-encryption=yes only-one=yes change-tcp-mss=yes use-upnp=default address-list="" 
     on-up="" on-down="" 
 2 * name="default-encryption" use-mpls=default use-compression=default use-encryption=yes only-one=default change-tcp-mss=yes 
     use-upnp=default address-list="" on-up="" on-down=""

Create an OpenVPN interface

Here we actually create an interface for the VPN connection. Important! Change xxx.xxx.xxx.xxx to your own server address (ip address or domain name). User/password properties seem to be mandatory on the client even if the server doesn't have auth-user-pass-verify enabled.

interface ovpn-client add name=ovpn-client connect-to=xxx.xxx.xxx.xxx port=1194 mode=ip user="openvpn" password="" profile=OVPN-client certificate=client.crt_0 auth=sha1 cipher=blowfish128 add-default-route=yes

Check out your new open-vpn connection:

interface ovpn-client print

Flags: X - disabled, R - running 
 0  R name="ovpn-client" mac-address=xx:xx:xx:xx:xx:xx max-mtu=1500 connect-to=xxx.xxx.xxx.xxx port=1194 mode=ip user="openvpn" password="" profile=OVPN-client certificate=client.crt_0 auth=sha1 cipher=blowfish128 add-default-route=yes

interface ovpn-client monitor 0

  status: connected
  uptime: 18h38m31s
  encoding: BF-128-CBC/SHA1
  mtu: 1500

Configure the firewall

ip firewall filter print

Flags: X - disabled, I - invalid, D - dynamic 
 0  D ;;; special dummy rule to show fasttrack counters
      chain=forward action=passthrough 
 1    ;;; fasttrack
      chain=forward action=fasttrack-connection connection-state=established,related log=no log-prefix="" 
 2    ;;; accept established,related
      chain=forward action=accept connection-state=established,related log=no log-prefix="" 
 3    ;;; drop invalid
      chain=forward action=drop connection-state=invalid log=no log-prefix="" 
 4    ;;; drop all from WAN not DSTNATed
      chain=forward action=drop connection-state=new connection-nat-state=!dstnat in-interface=ether1 log=no log-prefix="" 
 5    chain=input action=accept protocol=icmp log=no log-prefix="" 
 6    chain=input action=accept connection-state=established log=no log-prefix="" 
 7    chain=input action=accept connection-state=related log=no log-prefix="" 
 8    chain=input action=drop in-interface=pppoe-out1 log=no log-prefix="" 

Configure masquerade

We add new masquerade NAT rule:

ip firewall nat add chain=srcnat action=masquerade out-interface=ovpn-client log=no log-prefix=""

Check out it:

ip firewall nat print

Flags: X - disabled, I - invalid, D - dynamic 
 0    chain=srcnat action=masquerade out-interface=pppoe-out1 log=no log-prefix="" 
 1    chain=srcnat action=masquerade out-interface=ovpn-client log=no log-prefix=""

Configure Policy Based Routing

Here we add some resources that we wanna using through our OpenVPN client. We can use domains or ip's in address:

ip firewall address-list add list="OpenVPN" address="somehost.com"
ip firewall address-list add list="OpenVPN" address="xxx.xxx.xxx.xxx"
ip firewall address-list add list="OpenVPN" address="xxx.xxx.xxx.xxx/xx"

Configure mangle

Then we set up mangle rule which marks packets coming from the local network and destined for the internet with a mark named 'vpn_traffic':

ip firewall mangle add chain=prerouting action=mark-routing new-routing-mark=vpn_traffic passthrough=yes dst-address-list=OpenVPN log=no

Check out it:

ip firewall mangle print

Flags: X - disabled, I - invalid, D - dynamic
 0  D ;;; special dummy rule to show fasttrack counters
      chain=prerouting action=passthrough
 1  D ;;; special dummy rule to show fasttrack counters
      chain=forward action=passthrough
 2  D ;;; special dummy rule to show fasttrack counters
      chain=postrouting action=passthrough
 3    chain=prerouting action=mark-routing new-routing-mark=vpn_traffic passthrough=yes dst-address-list=OpenVPN log=no log-prefix=""

Configure routing

Next we tell the router that all traffic with the 'vpn_traffic' mark should go through the VPN interface:

ip route add gateway="ovpn-client" type="unicast" routing-mark="vpn_traffic"

Check out it:

ip route print

Flags: X - disabled, A - active, D - dynamic, C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme, 
B - blackhole, U - unreachable, P - prohibit 
 #      DST-ADDRESS        PREF-SRC        GATEWAY            DISTANCE
 0 A S  0.0.0.0/0                          ovpn-client               1
 1 ADS  0.0.0.0/0                          10.10.1.4                 0
 2  DS  0.0.0.0/0                          10.0.0.1                  1
 3 ADC  10.0.0.1/32        10.0.0.6        ovpn-client               0
 4 ADC  10.10.1.4/32       10.10.16.25     pppoe-out1                0
 5 ADS  xxx.xxx.xxx.xxx/xx                 10.10.1.4                 0
 6 ADC  192.168.1.0/24     192.168.1.1     bridge                    0

Please note, if you not see ADS route with your OpenVPN server ip you have forgotten add-default-route=yes in your ovpn-client.

---

Using Policy Based Routing for disabling blocking resources by your ISP

If you want to use this manual for disabling blocking resources by your ISP, use not your ISP DNS. For instance you can use free DNS by Google (8.8.8.8 or 8.8.4.4).

Step 1. Disable providers DNS's.

Go to PPP > Interface > Your connection (in this case it's pppoe-out1) > Dial Out and disable 'Use Peer DNS' option.

interface pppoe-client set name="pppoe-out1" max-mtu=auto max-mru=auto mrru=disabled interface=ether1 user="########" password="########" profile=default keepalive-timeout=60 service-name="" ac-name="" add-default route=yes default-route-distance=0 dial-on-demand=no use-peer-dns=no allow=pap,chap,mschap1,mschap2

Step 2. Add new DNS.

ip dns set servers=8.8.8.8

Step 3. Clear your old DNS cache.

ip dns cache flush

---

Happy End

That's all! Your Mikrotik Policy Based Routing should now be routed through your OpenVPN server. Cheers!