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Damian Gardner

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DHCP fails to properly assign IP's for a 2nd subnet on network

Hello - we have a SuperScope on our 2008 R2 DGCP AD server, which runs DHCP for 2 subnets - 192.168.1.x and 192.168.5.x.  The respective VLANs for each subnet are VLAN2 & VLAN 6, respectively.  What we are seeing is the following scenario:

1) Computers that do not have a lease previously on the network (they have been off for several days) will be properly assigned a new lease on the 2nd subnet of 5.x on VLAN6, and work fine.  

2) Computers that have an active lease, however, on the 1st subnet of 1.x on VLAN2, will not receive a new IP on the 2nd subnet when they are in our neighboring building that has a WIFI network going thru a switch that is configured for VLAN6.  Cisco captured and inspected packets from test clients coming thru a VLAN6 port on the network, and see the DHCP Request is made by the client, and the DHCP server answers, but does not properly hand out a 5.x IP address - and the client ends up retaining the 1.x IP it had originally.  Even if we issue a "ipconfig /release" it does not help.  

3) If I hard-code a static address on the 5.x subnet, however, the client will connect properly.  

Is there something that is not configured correctly on the DHCP server to cause this?  I will attach a screenshot of our Superscope.  Let me know what else I can send that might help disagnose this.  

Thanks for your help!
* tcpipCiscoDHCPWindows NetworkingNetworking

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Damian Gardner

8/22/2022 - Mon