DHCP server on VLAN



  • Hello everybody

    I have created 3 vlans (10, 20 and 30) on a parent NIC type emx (Intel E1000 like seen as em3). I have enabled a DHCP server on each vlan with ranges 192.168.6.10-245/24, 7.10-245/24 and 8.10-245/24

    In the menu Status->Interfaces I verify :

    VLAN10 up interface vlan0 …
    VLAN20 up interface vlan1 ...
    and so on. The mac address of each vlan card is the mac address of the parent NIC. IP are OK

    On the switch I have a trunk port (1) where I have plugged my PFSense.server

    Example vlan 10 port 1 tagged, port 2 untagged
                vlan 20 port 1 tagged, port 3 untagged
    and so on

    On switch port 2 I have plugged a Debian machine with a NIC Intel E1000 like

    When I run a DHCP request (dhclient eth0) from my Debien machine I see a suite of DHCPDISCOVER until it fails ...

    In the PFSense logs I see the request : (newer top)

    DHCPOFFER on 192.168.6.245 to mac_address_client via vlan0
    DHCPDISCOVER from mac_address_client via vlan0

    I connect now my Debian to port 3 : same problem but with "via vlan1" with a good IP address given by DHCP. The switch config seems good.

    No logs in the firewall.

    I have changed the MTU to 1496 on one side on the other side or on the two sides looking Debian notes but the things continue going wrong.

    I have also changed the macc address of each vlan card without effect ...

    I don't know where I can go ?

    Any idea ?

    Anticipated thanks.

    Best regards.



  • Do you have hardware checksums enabled? If so, disable and try again.

    Suggest you run a tcpdump trace (type the shell command # tcpdump -i eth0) on the Debian system to make sure the DHCPOFFER from pfSense is being seen. It may be that tcpdump will show the DHCPOFFER and report a problem with it.



  • Hello everybody

    Where can I disable the hardware cheksum (Switch, PFsense …) ?

    I have ran a tcpdum client side, server side and I have read the capture with wireshark.

    Server side I see frame in for DHCPREQUEST and the frame out for the DHCPOFFER. All seems go right but never arrive to the client.

    I have tried the same capture with a ping and all is OK server side but nothing arrive on the client.

    I think this is a switch problem, it is an old Netgear FS726T and the 802.1Q is probably a little buggy.

    News on Tuesday.

    Best regards





  • Thank you everybody,

    I have disabled the hardware checksum, I have also changed the model of NIC without success.

    I think that my switch has an implementation 802.1q buggy.

    Question : if I plug a cross cable between my server and my client Debian on which I have installed and configured the vlan packet, is it functional ?

    Best regards.



  • @tux3132:

    I think that my switch has an implementation 802.1q buggy.

    Might be worth checking the switch support web pages to so see if there is a firmware upgrade or if others have reported similar problems. What switch are you using?

    @tux3132:

    Question : if I plug a cross cable between my server and my client Debian on which I have installed and configured the vlan packet, is it functional ?

    If both ends of the cable support VLANs and are configured compatibly it should work. (I know nothing about configuring VLANs in Linux.) You probably won't need a cross over cable since it seems your NICs are pretty modern. Using a cross over cable won't hurt.


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