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DCHP relay agent (Help)

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  • DCHP relay agent (Help)

    I am currently doing a lab, which entails having two subnets each of which contain 1 ( 2008 RRAS server for LAN routing and DHCP relay agent) (one 2008 dhcp server configured with scopes for each subnet) and (one DHCP client). The main goal of this lab is to get DHCP address to you client in the event you primary DHCP server goes down and it should work in both directions. I have added DCHP relay agents to both RRAS servers and configured the correct adapter to point to the DHCP server on the other subnet. All nodes on the network can communicate with each other just fine, but when i bring down one of the DHCP servers, the Relay agent isn't forwarding the requests. I've fallowed all the documentation i can find and everything appears to be correct. Does anyone have any idea of what is going wrong with my setup???

    My Diagram is below...
    Attached Files

  • #2
    Re: DCHP relay agent (Help)

    Just a thought but, has the DHCP lease expired on the client machine to allow the DHCP relay to provide another IP addess lease.

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    • #3
      Re: DCHP relay agent (Help)

      Yes once I shutdown/disconnect my dhcp server i preform an ipconfig /release and /renew on my client in an attempt to get an address from the dhcp server on the other subnet. No luck my dchp request just seems to timeout. error message below.

      "An error pccurred while renewing interface Local Area Connection : unable to contact your DHCP server, Request has timed out."

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      • #4
        Re: DCHP relay agent (Help)

        Do you have routes (static or otherwise) in place to tell your clients how to get from one subnet to the other? Last time I set something like this up I was using HP ProCurve switches and the IP Helper option needed to be set there along with a static route on the default gateway pointing to the switch as the gateway to the second subnet.
        BSc, MCSA: Server 2008, MCSE, MCSA: Messaging, MCTS
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        • #5
          Re: DCHP relay agent (Help)

          So, its not clear, at least to me, where the DHCP server sits. You have two subnets each with a RRAS server, but what subnet does the DHCP server sit on?

          This is a pretty straightforward lab. If you have mutliple subnets, you do need to have routing set up properly. You mentioned that all clients can communicate so that would indicate to me that routing is set up properly.

          Then as far as the RRAS servers, the relay agents need to be configured on the interface (in RRAS) that the clients are on.

          With regard to the DHCp server, you just have to make sure that your scopes match the subnets where the relay agents are sitting.

          If needed, you could always start a network capture to help you track the flow of traffic between the networks.
          JM @ IT Training & Consulting
          http://www.itgeared.com

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          • #6
            Re: DCHP relay agent (Help)

            I have a DHCP server obn each subnet, and I should have DHCP relay working in both directions when the lab is finished. All routes have been setup and are working correctly. When I look at my Adapter attached to frame relay i notice it discard exactly half of my requests...

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            • #7
              Re: DCHP relay agent (Help)

              I understand your setup as follows:

              Two subnets. Each subnet has an RRAS Server w Relay, DHCP server, and client. What you are trying to do is have a client obtain a DHCP address from either DHCP server.

              What I do know is that if your Relay agent is working properly, what you should see (with a packet capture) are broadcast requests on the same side of the relay agent, and unicast packets coming from the relay agent to the DHCP server on the remote side. If you see the unicast packets, the relay is working, if you dont then your focus is on the relay configuration.

              This is a pretty straightforward design. So, I am not sure about the "frame relay" and discarding of requests.... This may not be a DHCP problem but something with your frame relay configuration?
              JM @ IT Training & Consulting
              http://www.itgeared.com

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              • #8
                Re: DCHP relay agent (Help)

                Thank you all for you help!!! But I figured out what my issue was, after using wireshark to examine my DHCP packets.. Any yes your right JM prob wasn't wit my relay agent it ended up being a problem with my scope... In the advanced tab i changed it from the BOOTP option to the BOTH option and it solved my issue... I'm a little sad i didn't figure it out sooner.

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                • #9
                  Re: DCHP relay agent (Help)

                  The important thing is that you were able to work through the issue and gain additional experience.
                  JM @ IT Training & Consulting
                  http://www.itgeared.com

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