Help troubleshooting a weird DHCP issue. pfSense not responding to DHCPDISCOVER



  • I have something weird going on with my setup, and could use some help and/or suggestions on how to troubleshoot this.

    I have a pfSense machine that is plugged into a Cisco 3560 switch.  That switch is the main switch for my entire house, with no other switch gear in the network.

    My problem is that I am able to get a DHCP address for every single device in my network….except one.  A Raspberry Pi2.  This RPi2 was destined to be a Plex Media Player machine, but I cannot get it to get a DHCP address.  I have tried running a few different distros on it, and it will randomly get an IP address from pfSense, but thats a very rare occasion.

    I have done the following to troubleshoot:  I have configured a port/session monitoring on my Cisco switch such that it looks like this:

    sw1>show monitor session 1
    Session 1

    Type                  : Local Session
    Source Ports          :
        Both              : Gi0/5,Gi0/24
    Destination Ports      : Gi0/3
        Encapsulation      : Native
              Ingress      : Disabled

    Ports GiO/5 is the port my Raspberry Pi is on and port Gi0/24 is the port for my pfSense machine.  These are setup as source ports for the monitoring session, and its supposed to send a "copy" of all the traffic to port Gi0/3, which is a port in my office that I have plugged into an ethernet adapter on my Mac that is running a packet capture on the ethernet adapter, so as to capture the flow of packets from both the pfSense machine as well as the RPi2.

    When I filter just for bootp traffic, I can see the Raspberry Pi2 send about 6 DHCPDISCOVER packets spaced about 5 seconds apart.  However, I DO NOT see my pfSense machine returning any DHCPOFFER packets at all.  Likewise, looking in the logs of the pfSense machine, I do not see anything in the dhcpd logs.

    I guess where I have having trouble is trying to find out if the DHCPDISCOVER packets are even making it out of the switch or if the pfSense machine is just ignoring them for some reason.  I am not very strong with Cisco iOS, so I am not sure how to troubleshoot fully on that end.  I have tried the Pi2 in several different network jacks with same results.

    The only thing I haven't tried yet, which I might in a few, is to plug the Pi2 Directly into the pfSense machine (where I have my Cisco plugged) to see if it can make a DHCPDISCOVER and get a response in the logs.

    I know this problem could possibly span outside the scope of my pfSense machine and be an issue in my switch, but I wanted to post here because there is a lot of smart networking folks that may have seen this before or could tell me where to check next.

    Thanks in advance!



  • I guess where I have having trouble is trying to find out if the DHCPDISCOVER packets are even making it out of the switch or if the pfSense machine is just ignoring them for some reason.  I am not very strong with Cisco iOS, so I am not sure how to troubleshoot fully on that end.  I have tried the Pi2 in several different network jacks with same results.

    Couple of things you could do to determine this. Firstly, you could set up a SPAN port on your Cisco switch, capture the egress traffic on interface Gi0/24. You could also use tcpdump from the pfSense shell and filter by the MAC address of the Pi.

    tcpdump host aa:bb:cc:11:22:33
    

    You could even use the basic packet capture facility in pfSense under Diagnostics > Packet Capture however this is fairly limited.



  • I run DHCP from my Cisco layer 3 switch and not pfsense.  I guess this might be another option.


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