IPsec VPN Mikrotik to Linux

After writing the Mikrotik IPsec VPN article and I got some questions about how Mikrotik will work with a Linux device to build an IPsec VPN. I did notice that the questions were more oriented for a copy / paste solution, so I’ll provide one that it’s working. If you need more details about why the solution is like it this, please let me know.
Also don’t forget to customize the solution as you need.

I’ll start with the same topology like in the last post, just that the right side now it’s a Linux device.

Mikrotik-IPsec-VPN-Linux

Please consider the minimum ports needed to be open on your firewall from my earlier article. Just don’t forget to open these ports also on the Linux device.

First let’s configure the Mikrotik.

The IPsec Proposal

CLI

ip ipsec proposal add name=MyProposal auth-algorithms=sha1 enc-algorithms=aes-256-cbc pfs-group=none

GUI

IP > IPsec > Proposals

Name: MyProposal
Auth. Algorithm: sha1
Encr. Algorithm: aes-256 cbc
PFS Group: none

The IPsec Policy

CLI

ip ipsec policy add src-address=192.168.0.0/24 dst-address=172.30.0.0/24 protocol=all action=encrypt level=require ipsec-protocols=esp tunnel=yes sa-src-address=11.11.11.11 sa-dst-address=22.22.22.22 proposal=MyProposal

GUI

IP > IPsec > Policies

SRC ADDR: 192.168.0.0/24
DST ADDR: 172.30.0.0/24
Protocol: all
Action: Encrypt
Level: require
IPsec protocols: esp
Tunnel: check
SA SRC: 11.11.11.11
SA DST: 22.22.22.22
Proposal: MyProposal

The IPsec Peer

CLI

ip ipsec peer add address=22.22.22.22 port=500 auth-method=pre-shared-key secret=my_preshared_key exchange-mode=main send-initial-contact=yes nat-traversal=yes proposal-check=obey hash-algorithm=sha1 enc-algorithm=3des,aes-128 dh-group=modp1024 generate-policy=no

GUI

IP > IPsec > Peers

Address: 22.22.22.22
Port: 500
Auth. Method: pre shared key
Passive: not checked
Secret: my_preshared_key
Policy Template Group: default
Exchange mode: main
Send Initial Contact: checked
NAT Traversal: checked
My ID: Auto - empty
Proposal Check: obey
Hash Algorithm: sha1
Encryptions Algorithm: 3des aes-128
DH Group: modp1024
Generate policy: no

Now, the Linux part. I’m using Ubuntu, but I’m not going to advocate here for one flavour or another. So, just use any device with Linux or you try solutions such as Amazon AWS. Install Openswan (compile it from source or install via your Linux flavour package system).

The main file for Openswan is ipsec.conf. For me this file is in /etc, but I assume it can reside in another location.

For the above example, the ipsec.conf file looks like this:

version 2.0

# basic configuration
config setup
        nat_traversal=yes
        oe=off
        protostack=netkey
        force_keepalive=yes
        keep_alive=60
        #nhelpers=0

# Add connections here
conn mikrotik-to-linux
        authby=secret
        auto=start
        type=tunnel
        left=22.22.22.22
        leftid=22.22.22.22
        leftsourceip=172.30.0.1
        leftsubnet=172.30.0.0/24
        right=11.11.11.11
        rightsubnet=192.168.0.0/24
        rightid=11.11.11.11
        pfs=no
        forceencaps=yes
        ike=aes256-sha1;modp1024
        phase2=esp
        phase2alg=aes256-sha1

You need to associate the keyword “left” with “local” and “right” with “remote” and it will be easier to read the configuration above.

Also in the /etc location I have another file called ipsec.secrets which has the pre-shared secret key:

22.22.22.22 11.11.11.11 : PSK "my_preshared_key"

This is the minimal configuration that I need to apply to have the IPsec VPN up and running. I’m sure that it can be fine tuned to add more security or features, but that is not in scope of this post.

As always if you have problems please let me know in Comments.

Published by

Calin

Calin is a network engineer, with more than 15 years of experience in designing, installing, troubleshooting, and maintaining large enterprise WAN and LAN networks.

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