DHCP leases out of WAN interface?

  • Hi all - I have the following set up as a little lab environment:

    ISP wifi router: IP, with DHCP for other devices (phones, laptops etc) on the network

    PfSense VM: WAN port: IP, LAN port:

    Lab server VMs: various IPs on the network

    All works as intended, if I use fixed IPs on the Lab network. However, I'd like to be able to use DHCP on the Lab network so I don't have to manage all those IPs manually. I've tried doing this a couple of ways, by using a Windows 2012 DNS server and by using PfSense's in-built DHCP server on its LAN interface, but both hit the same weird problem:

    Devices out on the network, attached via Wifi to the ISP router, are given DHCP leases from the server. This means that they break in various ways.

    Why is this happening? My understanding is that DHCP should not traverse the PfSense router at all, and there should be no way for DHCP leases to be handed out of the WAN interfaces.

  • You definitely have something misconfigured.  Out of the box, pfSense wouldn't respond to any DHCPREQUEST from WAN.  You either have something cabled wrong and you're running multiple networks on the same wire, or you have done something strange in pfSense.

  • I have a very basic config config, pretty much all I've done is add a fixed IP on the LAN port and let the WAN port receive it's IP from DHCP with a reserved address. I don't see what I could have done to break anything - any suggestions?

    Also in terms of the networking - again it's very basic, there's only one 'cable' and just the two networks, so I can't see what I could have misconfigured?

  • The only way a DHCP server could be sending out leases to the WAN is if there are requests coming in.  That shouldn't be happening, if you haven't opened up the firewall to allow it.  What does Packet capture show?

  • so I can't see what I could have misconfigured?

    Neither can we because we can't see what you've done.  Post screens of your WAN and LAN interface details, your DHCP Server config and your WAN rules.

    You didn't happen to enable the DHCP Relay, did you?

  • Not sure if this would be helpful but I had the same issue while I was building the firewall as my firewall was not sitting directly behind the router. As already suggested above this sounds more like a misconfiguration.  It may sound silly but make sure that you have: ROUTER/WAN -> FIREWALL -> SWITCH/LAN and Not ROUTER/WAN -> SWITCH/LAN -> FIREWALL.

  • LAYER 8 Netgate

    It is obvious to me that the pfSense LAN device can "see" the DHCP requests from the network you think is in front of the firewall.

    It obviously is misconfigured.

    I would packet capture on the SWITCH that is on the network. If you can see the MAC addresses of the devices that are supposed to be on network you have somehow crossed the streams.

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