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DHCP assigned duplicate IP

ArunGupta

In UTM9, I have configured a DHCP server. Using the "Make Static" button, I created a fixed IP for a laptop (192.168.250.238). This is working fine, I have been using it for more than a year now. In the meantime, I added some more DHCP devices, including a Roku express. The Roku express has also been working fine for last 2 months. Yesterday, it stopped working, complaining about internet connectivity. On checking the network settings, I found that DHCP server had assigned the laptop's IP address (192.168.250.238) to the Roku express. There is no way to release the lease manually. The lease time is set to just 2 hours, but the DHCP server keeps assigning the same IP to the Roku even when the laptop is on and is already assigned that IP. I have restarted the Roku many times, but the it is not getting a new IP. I also noticed that Roku has been assigned three DNS servers, 192.168.250.1 (which is configure in UTM9 DHCP settings) and Google's public DNS servers, 8.8.8.8 and 4.4.4.4 and I have no idea where these servers are coming from. How can this happen? Any explanation?

Thanks,

Arun



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  • +1

    DHCP in the UTM doesn't work like it does in a Windows Server.  In Windows, "Reservations" are made, and there are none of those in the UTM.  You must assign static IPs outside of the dynamic range assigned by the DHCP server.  Was that the issue?

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
  • 0 in reply to BAlfson

    Okay. My fault. I did not do the RTFM properly. It is clearly documented in the UTM9 documentation:

    • Make the following settings:

      Action: Select Create a new host.

      Name: Enter a descriptive name for the new host.

      DHCP server: Select the DHCP server to be used for static mapping. The corresponding DHCP range is displayed below the drop-down list.

      IPv4 address: Change the IP address to an address outside the DHCP pool range.

      Note – When converting a lease to a static mapping you should change the IP address so that it is no longer inside the scope of the DHCP pool. However, if you change the IP address, the address used by the client will not change immediately, but only when it tries to renew its lease for the next time.

    So, the UTM9 is working as documented. Thanks Bob for pointing it out.

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  • 0 in reply to BAlfson

    Okay. My fault. I did not do the RTFM properly. It is clearly documented in the UTM9 documentation:

    • Make the following settings:

      Action: Select Create a new host.

      Name: Enter a descriptive name for the new host.

      DHCP server: Select the DHCP server to be used for static mapping. The corresponding DHCP range is displayed below the drop-down list.

      IPv4 address: Change the IP address to an address outside the DHCP pool range.

      Note – When converting a lease to a static mapping you should change the IP address so that it is no longer inside the scope of the DHCP pool. However, if you change the IP address, the address used by the client will not change immediately, but only when it tries to renew its lease for the next time.

    So, the UTM9 is working as documented. Thanks Bob for pointing it out.

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