PiHole DHCP not giving address when connecting via OpenVPN

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1

Sorry for additional post, but I haven't been able to get any insights to solving this yet.

OpenVPN (SoftEther server) works fine using PiHole and my router DHCP.

When I switched to PiHole for DHCP (and turned off the Router DHCP), everything works fine, except for OpenVPN does not connect and gives Authentication Failed.

I switched back to router DHCP and OpenVPN is still ok. Just something with the PiHole DHCP and OpenVPN that I'm missing here.

Is there something else needed to route the OpenVPN client to the PiHole DHCP specifically? All other DHCP connects work fine.

Expected Behaviour:

I would expect that the OpenVPN worked same whether using the Router DHCP or Pi-Hole DHCP.

Actual Behaviour:

When using the Pi-Hole DHCP, I get the following error in OpenVPN.

It looks like the OpenVPN is not seeing the PiHole DHCP. PiHole DHCP is working well for all the other client connections, but for some reason, not the SoftEther OpenVPN server. When I use the Router DHCP, then the Softether OpenVPN works ok.

"Channel 0: Acquiring an IP address from the DHCP server failed. To accept a PPP session, you need to have a DHCP server. Make sure that a DHCP server is working normally in the Ethernet segment which the Virtual Hub belongs to. If you do not have a DHCP server, you can use the Virtual DHCP function of the SecureNAT on the Virtual Hub instead."

Generated Debug Log: https://tricorder.pi-hole.net/rH79c5ey/

2

DHCP relies on broadcast packets for operation. This means that only clients and servers on the same network segment are able to configure via DHCP. If you want clients outside of the network segment then you'll need to use a DHCP helper or DHCP relay between the network segments.

A quick search of OpenVPN and DHCP relay mentions layer-2 bridging as an option as well.

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Dan, thanks for the info. What I still don't understand is that the DHCP from the Linksys works for OpenVPN, but just not OpenVPN with the PiHole DHCP. Linksys and PiHole are both on the same network, so not sure why a layer-2 bridging would be needed. Normal Operation the DHCP is working great either with Linksys Router or with PiHole (Linksys disabled).

Using OPENVPN, works with Linksys DHCP no problem, but not with PiHole DHCP.

Do you have any additional insight here, on the difference? Any debugging things I can try to verify?

Thanks, Carl

4

Your VPN server is operating its own virtual link. Your Pi-hole machine has to be on that same link.

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