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David_Collins
David_Collins
New Member
February 16, 2012
Question

Device not receiving DHCP address

  • February 16, 2012
  • 7 replies
  • 24245 views
I am using a FortiGate 50B in my office (running 4.0 MR2), and we have it configured with several VLANs, and each VLAN has a DHCP server configured in the FortiGate. We also have a WAP configured with multiple SSIDs, one for each of the VLANs I am having an issue with a laptop in my office that is not getting an IP address through DHCP from the router. The problem only occurs with this one laptop when it tries to connect to VLAN2, and only wirelessly. If the laptop is connected hard-wired to VLAN2, or it connects wirelessly or hard-wired to any of the other VLANs, it works fine. If I set a static IP for the laptop, and connect wirelessly to VLAN2, it works fine. The machine is running WinXP. All other devices on the network are receiving their IP assignments properly. When I look at the logs, I see that sometimes the laptop is trying to find a DHCP server, and the router responds, but the laptop never sees the response. Other times, the laptop will make it past that step and will then ask for an address assignment, and the router is responds back with an IP address assignment for it, reserving that IP in the DHCP table, but the laptop never sees that response back with the assigned IP. The laptop will ask again a few moments later, and never see the response back from the router. So the entries in the log look something like: A client broadcasts a DHCPDISCOVER message Server responds with offer of configuration parameters A client broadcasts a DHCPDISCOVER message Server responds with offer of configuration parameters A client broadcasts a DHCPDISCOVER message Server responds with offer of configuration parameters or other times like: A client broadcasts a DHCPDISCOVER message Server responds with offer of configuration parameters Client requests IP address/configuration parameters Assigns IP address/configuration parameters to the client Client requests IP address/configuration parameters Assigns IP address/configuration parameters to the client Client requests IP address/configuration parameters Assigns IP address/configuration parameters to the client It would seem that this is an issue more with the laptop, and not the router, but I am at a loss of why this might be happening for this one VLAN only. Any suggestions on what I can do to troubleshoot this further? Thanks.

    7 replies

    Federico_Vecchiatti
    Federico_Vecchiatti
    New Member
    February 16, 2012
    Same problem here. Two DHCP relay defined on two different interface, wifi devices are not getting ip. Removing one dhcp relay (that I added yesterday) users are now able to connect again. Same debug at the DHCP server. 4.0 MR2 Patch 10. I' ve opened a ticket, but I see that I' m not alone. Federico
    emnoc
    emnoc
    New Member
    February 16, 2012
    Just curious, have you ran wireshark on the effected machine to see if the DHCP offer is being pass thru the 802.11 network back to the client? If you only have one machine exhibiting a problem, than I would suspect it' s that host imho suggestion: I know my wireless overlay won' t allow for DHCP-offer outside of the approved dhc-servers that we have instances for .
    rwpatterson
    rwpatterson
    New Member
    February 16, 2012
    Welcome to the forums. Can ANY device receive an IP on that SSID?
    David_Collins
    David_CollinsAuthor
    New Member
    February 16, 2012
    Can ANY device receive an IP on that SSID?
    Yes, ALL other devices on that SSID are receiving IP addresses. Other laptops, iPhones, etc... One thing I did notice, and forgot to mention above, is that when the router reserves the IP address for the laptop having trouble, it shows up in the list, but the expiration time is only a couple minutes, where all the other leases are for 1 week. I don' t know if this is normal behavior for the router or not. I could see it issuing a short-term lease to get the process started, then bumping it to the full lease period after the negotiation is complete, but in this case the process doesn' t complete. That' s just a guess.
    Two DHCP relay defined on two different interface, wifi devices are not getting ip.
    It sounds like your problem might be a little different. I only have one device that isn' t getting an IP. Perhaps they are related in some way, though.
    Just curious, have you ran wireshark on the effected machine to see if the DHCP offer is being pass thru the 802.11 network back to the client?
    I haven' t done any packet captures yet. That laptop is not in the office today, but I was planning on doing that the next chance I get.
    emnoc
    emnoc
    New Member
    February 16, 2012
    one more thing, I see you have or assuming reservations, if this is correct. What if you don' t reserve an address for this client, Does the client get accepts a blind offer? it might something wrong with the client reservation e.g mac_address dhcp vrs bootp etc.... So just review your configurations with regards to the reservation.
    rwpatterson
    rwpatterson
    New Member
    February 16, 2012
    If you do have a reservation, it must be inside the DHCP scope, not outside.
    David_Collins
    David_CollinsAuthor
    New Member
    February 17, 2012
    Sorry for the confusion; I am not using any DHCP reservations on any of the VLANs. I should not have used the term " reservation" in that context. I was referring to the way the router will offer an IP address when asked for one, and then hold that address aside for the client until the negotiation is complete, at which point the IP address is " leased." I' ll do some more testing when I have that laptop available and follow up with the results. Thanks for the help.
    Federico_Vecchiatti
    Federico_Vecchiatti
    New Member
    February 17, 2012
    For us, problem with DHCP started when we added a second DHCP relay configuration. At that point, clients under the first DHCP_relay were not able to get the IP address (only wifi clients, cabled users were working fine). We had to remove the second DHCP relay configuration to fix the problem. The tcpdump at the DHCP servers show the DHCP flow completed. Federico
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