HOWTO: OPNsense and Wireguard to AirVPN

[Sj0rs 3]

This HOWTO describes how to connect to AirVPN with a Wireguard VPN tunnel from OPNsense.
This is the first draft of this howto, i might add (more) screenshots later on.
 

• Version: 0.1
• Date: 20231029

What we are going to achieve

1. We'll create a single Wireguard VPN Tunnel, IPv4 Only.
2. Traffic to the tunnel will be NATted

Requirements

1. OPNsense firewall is up-and-running and updated. This howto is based on version 23.7.7_1
2. You have basic knowledge on using OPNsense i.e. firewall rules, NAT, routing, gateways and aliases.
3. AirVPN Premium Access

Step 1. Information gathering
We'll grab some info that we need to configure the Wireguard Tunnel.

1. Go to the Client Area.
2. Got to VPN Devices.
3. Add a device or edit your existing device.
4. Note your Public Key and IPv4 under the heading "Wireguard"
5. Go back to the Client Aerea.
6. Go to Config Generator
7. Select "router" under "Choose your OS"
8. Select "Wireguard under "Choose protocols"
9. Select your country under "By Countries". I selected Netherlands
10. Scroll way down and download your config.

This is an example of a Wireguard config:
(the keys and IP are random and will not work, use your own)
 

[Interface]
Address = 10.45.95.123/32
PrivateKey = X72xgdx23XDomnSXmcy#S4Jc#9Y5G*vU$wg^n499yn6
MTU = 1320
DNS = 10.128.0.1

[Peer]
PublicKey = VTSQ77Uk4^&RY4h%S$#9h8PR2T&xyya&yPTtk6oD^m$
PresharedKey = b7&&7bntmCS5q%&4J*mSKBAUvV4XEqHerwscvbappXQ
Endpoint = nl3.vpn.airdns.org:1637
AllowedIPs = 0.0.0.0/0
PersistentKeepalive = 15

Step 2. Create the Tunnel configuration
Peer configuration:

1. in OPNsense go to VPN|Wireguard|Settings|Peers.
2. Create a peer with the following information:
   1. Name: wg_airvpn_<country code>. mine is called wg_airvpn_nl
   2. Public key: <PublicKey under heading [Peer] of your generated WG Config>
   3. Pre-shared key <presharedKey under heading [Peer] of your generated WG Config>
   4. Allowed IP's: 0.0.0.0/0
   5. Endpoint Address: <Endpoint under heading [Peer] of your generated WG Config>
   6. Endpoint port: 1637 (default port)
   7. Keepalive interval: 15 (default interval)

Instance configuration:

1. in OPNsense go to VPN|Wireguard|Settings|Instances
2. Create an instance with the following information:
   1. Enable Advanced Mode.
   2. Name: <Endpoint Name i.e. nl.vpn.airdns.org>
   3. Public Key: <Public Key as noted with step 1.4>
   4. Private Key: <PrivateKey under heading [Interface] of your generated WG Config>
   5. Listen Port: 1637
   6. MTU: 1320
   7. Tunnel Address: <Address including /32 under harding [Interface] of your generated WG Config>
   8. Peers: <select peer that you created with step 2.2>
   9. Disable routes: Enabled.

Step 3. Make an exception on your WAN interface

1. in OPNsense go to Firewall|Rules
2. Select your WAN interface, mine is called WAN_PPPOE
3. Create a Pass rule for IPv4/UDP port 1647 to your WAN-address.

Step 4. Assign Wireguard Interface

1. in OPNsense go to Interfaces|Assignments
2. You'll find a "wg1(Wireguard - nl.vpn.airdns.org)" (or similiar) interface.
3. bind it to an interface with a name of your choice. mine is called WAN_WG1 as is is the first site-to-site Wireguard tunnel on my WAN interface.

Step 5. Create a gateway.
Remember we disabled the routes for the WG instance configuration? Because of that we need to create a gateway.

1. In OPNsense go to System|Gateways|Single
2. Add a Gateway with the following information:
   1. Name: WAN_WG_GW
   2. Description: Interface WAN_WG1 Gateway
   3. Interface: Select WAN_WG1 as created in step 4.
   4. Address Family: IPv4
   5. IP address: Dynamic (leave empty)
   6. Far Gateway: Enabled (this i am not sure of but for now i'm happy it works)
   7. Disable Gateway Monitoring: enabled

Step 6. Aliases
We set up some aliases. This will make it more easy to redirect some hosts or networks to the Wireguard tunnel.

1. in OPNsense, go to Firewall|Aliases
2. Create host entries for the specific hosts you'll redirect
3. Create network entries for the specific network(s) you'll redirect.
4. Create a Network Group Entry with the host and network entries to group them together. My alias is called networkgroup_wireguard

Step 7. Create Outbound NAT for Wireguard.
(In my setup, i use Manual Outbound Rule Generation because i like to have control)

1. In OPNsense go to Firewall|NAT|Outbound
2. Create a new Outbound NAT rule with the following information:
   1. Interface: WAN_WG1
   2. TCP/IP version: IPv4
   3. Protocol: Any
   4. Source Address: <alias networkgroup_wireguard from step 6>
   5. Translation /target WAN_WG1 address
   6. Description: Wireguard VPN Outbound NAT rule

Step 8. Create Outbound Redirect rule.
In this example we create 2 rules on our LAN interface, one for redirecting to WG, the other to prevent leaks.

1. In OPNsense go to Firewall|Rules
2. Select your LAN interface
3. add an outbound Pass rule:
   1. Action: Pass
   2. Source: Networkgroup_wireguard
   3. Destination: Any (in my case i use an inverted network group called networkgroup_local where all my local vlans are grouped together)
   4. Gateway: WAN_WG1_GW (the gateway you created in step 5.)
4. Add an outbound block rule below that:
   1. Action: Block
   2. Source: Networkgroup_wireguard
   3. Destination: Any
   4. Gateway: default

Your WG VPN tunnel should now work. Test with https://ipleak.net

The following steps are more advanced and i'm still finetuning/experimenting with the settings. your experience may vary.

Step 9. Prevent VPN leakage
I'm new to OPNsense and i am not sure what the default setting is, but from my pfSense experience i know the following setting is important when you want to make sure your VPN does not leak when for instance the tunnel is down.

1. In OPNsense go to Firewall|Settings|Advanced
2. Under "Gateway Monitoring" enable "Skip Rules when gateway is down"

Step 10. MTU/MSS optimization
For now i have set thte MTU according to the default setting of AirVPN. I want it to be higher but for now i'm just happy it works.
My settings are as follows:

1. In the properties of the WAN_WG1 interface i set the MTU to 1320 and the MSS to 1280.
2. I created a normalize rule (Firewall|Settings|Normalization) with the following settings. this should enable me to clamp the MSS to 1280 for the wireguard group but leave the MSS to the desired setting (1452) as defined on my LAN interface for the rest of the hosts on my LAN;
   1. Interface: LAN
   2. Direction, Protocol: Any
   3. Source: networkgroup_wireguard
   4. Max MSS: 1280

 

[OpenSourcerer 1468]

Guides are always appreciated, thank you for the time you invested into it. Screenshots would be a blast.

[OPN-UserGuide 2]

This guide is outdated, please consider using this guide:
 

[kaymio 7]

Thank you for this HowTo. Seems to work great, though running just a few minutes and only checked for leaks.

Did you put this in a Network Security Forum to get it checked?

What would be needed to also enable IPv6?

[sse450 1]

Thank you for this post.

How to make an exemption for one of the PCs on LAN so that it can go out without VPN.

 

[OPN-UserGuide 2]

On 4/8/2024 at 9:23 PM, kaymio said:

Thank you for this HowTo. Seems to work great, though running just a few minutes and only checked for leaks.

Did you put this in a Network Security Forum to get it checked?

What would be needed to also enable IPv6?

Hi, I only saw your post today.
Which Forum you mean ?

I have not planned to include IPv6, but I will look into this. It might take a while, as I need to start from the scratch to make sure I got everything covered.

 

6 hours ago, sse450 said:

Thank you for this post.

How to make an exemption for one of the PCs on LAN so that it can go out without VPN.

 

If the client in on the LAN interface. Create a rule which is on top of the VPN out rule. Source the one client, destination any. Gateway the WAN GW
That should do it.

[sse450 1]

Many thanks for the help.

Actually, our office people complained about our VOIP as they cannot call outside. In a panic, I had to reverse all the rules I created in this how to.
I would like to re-enable them. But before it, UDP ports 5060, 10000-20000 should be open freely to get a working VOIP. Somehow, the rules in this how to prevented these ports. Following the disble all the steps, VOIP startted working.

Please find below a screenshot from my NAT | Port Forward and WAN rules.

I would appreciate any hint.
 

[go558a83nk 371]

1 hour ago, sse450 said:

Many thanks for the help.

Actually, our office people complained about our VOIP as they cannot call outside. In a panic, I had to reverse all the rules I created in this how to.
I would like to re-enable them. But before it, UDP ports 5060, 10000-20000 should be open freely to get a working VOIP. Somehow, the rules in this how to prevented these ports. Following the disble all the steps, VOIP startted working.

Please find below a screenshot from my NAT | Port Forward and WAN rules.

I would appreciate any hint.
 

You're looking at port forward and WAN rules which would control connections initiated from outside your network.  But aren't VoIP services reliant on first creating a connection to a server, therefore no port forwarding is required because the connection is initiated from your network?

I believe that's the case, therefore you need to be looking at your LAN rules.  Something prevented your VoIP devices from creating *outgoing* connections most likely.  Or if VoIP was forced out the VPN interface perhaps the VoIP service blocks connections from VPN servers.

[OPN-UserGuide 2]

Hi @sse450 I have to agree with @go558a83nk, if you would post your LAN rules that should help us to support you

[sse450 1]

Thank you for the support.

Attached is the LAN rules after disabling the rules (last three) in this how to. When they were enabled I had disabled the first two Default allow LAN to any rule as per the Step 8 ("You need to disable the existing Default rules"). Now you see them back to enabled after disabling VPN rules.

As far as I understand, disabling the default LAN rules prevents devices on LAN net go out freely without any VPN. I think I need to put a rule at the beginning of the rules for VOIP server (10.10.1.10) as source to allow destination any on WAN. This way VOIP server will act as if there is no VPN. Am I right?

[sse450 1]

Update:
I put an exemption rule for VPN_Free alias (composed of PCs to go out without VPN) at top of LAN Rules with all the other steps as described in this How To.

This time, the PCs in VPN_Free alias can not access any DNS server. I think, it needs an exemption for DNS server as well.

Sorry for my dumb questions. I am trying to wrap my head around firewall concept. Your help is much appreciated.


 

[OPN-UserGuide 2]

Yeah, my setup did not take any of this into consideration. Maybe I should add a warning.

Your issue is, as you mentioned, with the DNS not being available for those clients.
You need to add another rule, that's step 9 in my guide, but you do not need to create an extra alias, you got one already.

Try the following:

1. Create NAT port forward rule. Firewall → NAT → Port Forward
2. Click Add
3. Interface: LAN
4. TCP/IP Version: IPv4
5. Protocol: TCP/UDP (DNS traffic is usually UDP, but I thought it's better to do it like this)
6. Source: VPN_Free
7. Destination: This Firewall
8. Destination port range: DNS
9. Redirect target IP: This Firewall
10. Redirect target port: DNS
11. NAT reflection: Disable
12. Filter rule association: None

make sure this rule sits between the "Anti lockout" and "DNS to VPN" rule in my screenshot.
Let me know what the results are

edit: you could also see if excluding the "VPN_Free" alias from the "DNS to VPN" rule does the trick (instead of adding another rule). Make sure to test if you got DNS leaks in any case.

[sse450 1]

Thank you very much for your kind help. It worked.

With a small quirk.

15 hours ago, OPN-UserGuide said:

Redirect target IP: This Firewall 

There is no "This Firewall" option here. Instead I entered IP of the OPNsense (10.10.1.1).
 

15 hours ago, OPN-UserGuide said:

edit: you could also see if excluding the "VPN_Free" alias from the "DNS to VPN" rule does the trick (instead of adding another rule).

I think I should create a new alias as (LAN Net minus VPN_Free) instead of source whole LAN Net. I couldn't find a way to negate an alias within another alias. !VPN_Free is not working, at least I don't know how.

Without finding a way to use !VPN_Free in another alias, it is possible to do it long way as attached.

But, this time, there will be two aliases to maintain. In this case, first option looks more practical unless there is a way to negate an alias.
 

[sse450 1]

Trying to achieve forwarding port 9999 as per Step 10.

1. Created Firewall | Rule | WAN_WG1. Yes, I changed reply-to to  WAN_WG1_GW.
2. Created Firewall | NAT | Port Forward. With NAT reflection: Disable and Filter rule association: None.

Still, AirVPN client area says "No ports open". Probably, I am doing something wrong.

I would appreciate any help. Thank you.

[OPN-UserGuide 2]

This looks fine to me.

You need to have a service running on that port on client 192.168.2.10 btw to make the test work (imho).
You can also enable logging and check the logs during the test.

[DiSHd 0]

On 6/10/2024 at 9:48 PM, sse450 said:

Trying to achieve forwarding port 9999 as per Step 10.

1. Created Firewall | Rule | WAN_WG1. Yes, I changed reply-to to  WAN_WG1_GW.
2. Created Firewall | NAT | Port Forward. With NAT reflection: Disable and Filter rule association: None.

Still, AirVPN client area says "No ports open". Probably, I am doing something wrong.

I would appreciate any help. Thank you.

turn on NAT reflection. 
you only turn it off for redirecting LAN to LAN services on IPs that are directly accessible and thus dont require NAT.

[sapincher 0]

This guide did not fully work on OPNsense 24.7.8... Honestly I'm not sure it works at all. There are a few things to add to gateway rules to make it work.

On setting up the Wireguard instance, it is important that if "Disable routes" is checked, it is required that "advanced mode" is selected to enter a Gateway of 10.128.0.1 at the WG instance.

That same IP address of 10.128.0.1 should be used as the IPv4 address of the created Wireguard gateway and should be the same for all configurations for AirVPN.

Also why does this guide repeatedly reference port 1647 and forwarding that port out to WAN when it seems to me that port forwarding to WAN is completely unnecessary and 1647 is just a typo?

 

Edited ... by sapincher

[sapincher 0]

Also: It took me a while to figure out what was keeping port forwarding from the Wireguard interface to work on OPNsense, so hopefully the following helps somebody.

It turns out that with the default rules created by NAT port forwards on OPNsense, even if you correctly select your WG interface, OPNsense may correctly route through to your local device, but outbound traffic from that device will be sent via the default gateway. This is not useful.

Under Firewall -> NAT -> Port Forward, set up your port forward with your WG interface selected as the "Interface" and disable automatic rule generation and its buggy behavior (pic #1). If you are using a different external port than your internal/local port, this area is where you would add the external port to "Destination port range" and the internal port to "Redirect target port".

Under Firewall -> Rules -> [your_WG_interface], create a new rule with WG as your interface. Select the protocol to enable port range. Set your local device, making sure to change the /24 subnet to /32 to refer to a single specific address. If you are using different external/internal ports, only enter the internal port in this screen. Select the "default" gateway, not the WG interface. Click the "Advanced features" "Show/Hide" button to enable fixing the buggy behavior: clicking the "allow options" checkbox and setting the reply-to gateway as your WG gateway. Which, again, is 10.128.0.1 (pic #2).

You would think that, obviously, setting the gateway here to the WG interface instead of "default" would mean outbound traffic would be routed through that specific gateway. But you'd be wrong, and I don't know why.

You port forward exclusively with the WG interface and do not need to do anything with WAN, as you are using the WG gateway for internet and not WAN. So port forwarding with AirVPN works even if your ISP allots you an internal IP address for your WAN connection.
 

Edited ... by sapincher

[Nebulizer0031 0]

With the help of this thread, I managed to get it up and running.  However, I was having issues getting to some web pages.  After hours of troubleshooting and some help from ChatGPT, I appear to have it working now.  In case it helps someone, I needed to set MSS to 1300 on the Interface.  I don't pretend to fully understand why this helped.