DHCP Relay with Windows Server 2008 R2

Posted on 2011-10-18
Last Modified: 2012-05-12
Hi, We have a Windows 2008R2 DC which is also used as a DHCP server. The users are currently in the same IP range as the DHCP server which is 192.168.1.x. We are in the process of moving our users to a different subnet 10.0.1.x/16. A new VLAN has been created for this purpose on our Nortel switches. DHCP relay has been enabled on the Nortel 5520 and 4550 switches. The test desktops running XP & Windows 7 don't get an IP from the DHCP server although the DHCP server indicates that an IP has been leased to the MAC address of the test desktop. The test desktop is connected through an IP phone which has VLAN tagging. The ports on the switch are tagged with the new VLAN. Is there anything that is being overlooked to get DHCP working for the users on the new subnet?

Question by:cpcit
    LVL 4

    Expert Comment

    The port of your switch must be configured in a specific way to allow tagged trafic (IP Phone) and none-tagged trafic (pc).
    On Avaya/Nortel switches, this is done by configuring your port as "Untagged PVID Only", which will tag all your VLANs except one (your pc in your example)

    * Configure your port to "Untagged PVID Only" (It must be "tagged" currently)
    * Add VLAN "Ip Phone" to your port
    * Add VLAN "Pc" to your port
    * Configure the PVID of your port to the VLAN "Pc"
    * Check the config: both your Pc (with ip static first to test the VLAN config) and your IP Phone must have access to their respective gateway, through the same port.
    * Then you can debug the DHCP thing...

    Author Comment

    The port on the switch is already configured as "Untagged PVID only" with the default VLAN as "pc". Static IP on the pc works fine, its only the DHCP that is causing a problem.
    LVL 4

    Assisted Solution

    I guess you'll have to take a packet capture with Wireshark both on your pc and on the DHCP server, to see if the whole flow is ok.

    * Do packets arrive systematically to the DHCP server (It seems yes if a lease is granted, but we must be sure)
    * Do Pc receive an answer from the DHCP server ? If not, it maybe a route/VLAN problem on the way back, or a misconfiguration in the DHCP relay.

    A packet capture on the pc will definitely to narrow down the problem.

    Accepted Solution

    Thanks iwaxx. We managed to sort out the issue by using the second NIC on the DHCP server and tagging its port on the switch with "pc" VLAN as default. The desktops are now working fine with DHCP.

    Author Closing Comment

    Solution provided by iwaxx has partially correct although it was not the solution to the problem.

    Featured Post

    Highfive + Dolby Voice = No More Audio Complaints!

    Poor audio quality is one of the top reasons people don’t use video conferencing. Get the crispest, clearest audio powered by Dolby Voice in every meeting. Highfive and Dolby Voice deliver the best video conferencing and audio experience for every meeting and every room.

    Join & Write a Comment

    Ever wondered why you had to use DHCP options (dhcp opt 60, 66 or 67) in order to use PXE? Well, you don't!
    A Cisco router can be configured as a DHCP Server. There are advantages and disadvantages in making your Cisco router work as DHCP Server. Almost all the features for windows DHCP can be configured on Cisco-based DHCP server. Some of the features me…
    how to add IIS SMTP to handle application/Scanner relays into office 365.
    This video is in connection to the article "The case of a missing mobile phone (". It will help one to understand clearly the steps to track a lost android phone.

    733 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    21 Experts available now in Live!

    Get 1:1 Help Now