Validating the WireGuard VPN Communication Flow in OPNsense

[marsk]

Hi,

To better understand what I was actually configuring in the OPNsense web UI, I created a logical diagram to help me.
The diagram (Attached file) shows how traffic flows through OPNsense when using a WireGuard VPN.

However, I need help verifying that the diagram is correct. Could you please verify it for me?

//marsk

[meyergru]

I think the main problem with the diagram is that it mixes different abstraction layers and then shows them as if they were consecutive hops in the packet path.

For example:

• The gateway and the VLAN interface are not really separate hops. From the client's point of view, the gateway normally is an IP address on the OPNsense VLAN interface.
• A WireGuard interface, instance and peer are not three consecutive network elements either. The instance provides the WireGuard interface, while the peer is configuration belonging to that instance.
• The firewall is not one single box which the packet passes only once. Filtering happens at specific interfaces/directions and state tracking is involved.
• With WireGuard there are also two packet layers: the inner IP packet and the outer encrypted UDP packet.

Very simplified, outbound traffic would look more like:

Code Select Expand

Client
-> VLAN
-> OPNsense VLAN interface
-> firewall / routing decision
-> WireGuard interface
-> WireGuard processing / peer selection / encryption
-> WAN interface
-> ISP / Internet
-> remote WireGuard peer

And incoming traffic:

Code Select Expand

remote WireGuard peer
-> Internet / ISP
-> WAN
-> firewall (encrypted UDP packet)
-> WireGuard processing / decryption
-> WireGuard interface
-> firewall / routing (inner IP packet)
-> VLAN interface
-> Client

So I would probably either draw a packet-flow diagram, or a configuration-object diagram showing the relationships between VLANs, interfaces, WireGuard instances and peers.

Mixing both concepts into one left-to-right chain is what makes the current diagram somewhat misleading.