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DHCP giving out out-of-scope addresses RRS feed

  • Question

  • I am in charge of IT for two schools in a single building (infants downstairs, juniors upstairs). Each school has it's own server, running MS Server 2012. Both schools are on the same domain with the same subnet, but they each have different IP ranges. Each server provides the DNS for the clients in its own range and each client has DNS set to its school's server.

    I have set up DHCP on each server. The scope for the infants is the infants' IP range and the scope for the juniors is the juniors' IP range. I have also set up many reservations for all the classroom PCs and the pupils' netbooks and iPads. However, I have noticed recently that some of the juniors' clients are being given infants' IP addresses and vice versa - even though many of them have IP reservations set up. If I go to DNS and DHCP on both servers and delete the incorrect IP addresses, then release and renew the addresses on the clients, they get their correct address again, but how could it have happened in the first place? Also, we have Ruckus wireless on our network. The zone director for each school is set up with the appropriate school's subnet mask, gateway and DNS settings, but if I turn the wifi off and on on my iPhone by a particular AP in the juniors, say, sometimes the phone is given a juniors IP address and sometimes it gets an infants IP.

    Is this to be expected on a shared domain or should I be concerned - especially as the DHCP IP reservations seem to be being overridden.

    I'm using a mix of Windows 7 and 10 clients.

    Thanks.

    Wednesday, May 24, 2017 1:54 PM

All replies

  • Hi Reinwood

    >>Both schools are on the same domain with the same subnet, but they each have different IP ranges.

    Did you configure two servers in different segments? If it is.

    The DHCP client requests an IP address by broadcasting a DHCPDiscover message to the local subnet.

    Generally, broadcast cannot pass different segments. So, please check your configuration to verity if you configure some devices like relay agent to allow DHCP messages to travel.

    Best Regards,

    Candy


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    Thursday, May 25, 2017 7:15 AM
  • Hi

    Thanks for the reply. To be honest, I'm not entirely sure if they're in different segments.

    The internet comes into a main router in the juniors, then one Cat5 cable goes from that router to a switch in the juniors' cabinet and then cables go from there to the juniors clients via other switches.

    Another Cat5 cable goes from the main router to a switch in the infants' cabinet downstairs and, again, cables go from there to the infants clients via other switches.

    Does this count as two different segments or do I need to put a router between the main router and the juniors' cabinet and another between the main router and the infants' cabinet? Sorry for being dim.

    Paul

    Thursday, May 25, 2017 11:37 AM
  • Hi Reinwood,

    >>I'm not entirely sure if they're in different segments.

    You could post the result of running ipconfig/all at the command prompt on the two servers to let us know if they are in different network segments.

    Best Regards,

    Candy


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    Friday, May 26, 2017 5:40 AM
  • Hi. Here are the results. The Primary DNS Suffix and DNS Suffix Search List are all the same domain name on both servers.

    INFANTS:

    Windows IP Configuration

       Host Name . . . . . . . . . . . . : SERVERINF
       Primary Dns Suffix  . . . . . . . : ****.local
       Node Type . . . . . . . . . . . . : Hybrid
       IP Routing Enabled. . . . . . . . : No
       WINS Proxy Enabled. . . . . . . . : No
       DNS Suffix Search List. . . . . . : ****.local

    Ethernet adapter Ethernet 2:

       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : Broadcom BCM5716C NetXtreme II GigE (NDIS
     VBD Client) #36
       Physical Address. . . . . . . . . : **-**-**-**-**-**
       DHCP Enabled. . . . . . . . . . . : Yes
       Autoconfiguration Enabled . . . . : Yes

    Ethernet adapter Ethernet:

       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : Broadcom BCM5716C NetXtreme II GigE (NDIS
     VBD Client) #35
       Physical Address. . . . . . . . . : **-**-**-**-**-**
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes
       IPv4 Address. . . . . . . . . . . : 10.75.92.10(Preferred)
       Subnet Mask . . . . . . . . . . . : 255.255.252.0
       Default Gateway . . . . . . . . . : 10.75.92.1
       DNS Servers . . . . . . . . . . . : 10.75.92.10
                                           10.75.124.10
       NetBIOS over Tcpip. . . . . . . . : Enabled

    Tunnel adapter isatap.{2605A1B6-F75A-4474-9CC9-DE89CCDF05D8}:

       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : Microsoft ISATAP Adapter
       Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes

    Tunnel adapter isatap.{9692019C-D646-4A49-9F90-C24F4A87909D}:

       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : Microsoft ISATAP Adapter #3
       Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes

    Tunnel adapter Teredo Tunneling Pseudo-Interface:

       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
       Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes

    JUNIORS:

    Windows IP Configuration

       Host Name . . . . . . . . . . . . : ServerJun
       Primary Dns Suffix  . . . . . . . : ****.local
       Node Type . . . . . . . . . . . . : Hybrid
       IP Routing Enabled. . . . . . . . : No
       WINS Proxy Enabled. . . . . . . . : No
       DNS Suffix Search List. . . . . . : ****.local

    Ethernet adapter Ethernet:

       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : HP Ethernet 1Gb 4-port 331i Adapter
       Physical Address. . . . . . . . . : **-**-**-**-**-**
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes
       IPv4 Address. . . . . . . . . . . : 10.75.124.10(Preferred)
       Subnet Mask . . . . . . . . . . . : 255.255.252.0
       Default Gateway . . . . . . . . . : 10.75.124.1
       DNS Servers . . . . . . . . . . . : 10.75.124.10
                                           127.0.0.1
       NetBIOS over Tcpip. . . . . . . . : Enabled

    Tunnel adapter Teredo Tunneling Pseudo-Interface:

       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
       Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes

    Tunnel adapter isatap.{B1FF47D7-FB38-4604-8340-5508CBF1D0DB}:

       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . :
       Description . . . . . . . . . . . : Microsoft ISATAP Adapter #2
       Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes

    Friday, May 26, 2017 9:04 AM
  • Hi Reinwood

    >>IPv4 Address. . . . . . . . . . . : 10.75.124.10(Preferred)
         Subnet Mask . . . . . . . . . . . : 255.255.252.0
        IPv4 Address. . . . . . . . . . . : 10.75.92.10(Preferred)
        Subnet Mask . . . . . . . . . . . : 255.255.252.0

    I checked your post and find that they are in the different network segment.

    As I said before, DHCPDiscover message cannot pass different segments generally. So, you should first check the configuration in you environment to verity if you configure some devices like relay agent to allow DHCP messages to travel.

    Best Regards,

    Candy


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    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.

    Monday, May 29, 2017 9:20 AM
  • Hi Reinwood,

    Just checking in to see if the information provided was helpful.

    Please let us know if you would like further assistance.

    Best Regards,

    Candy


    Please remember to mark the replies as answers if they help.
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    Thursday, June 1, 2017 7:56 AM
  • Hi

    Sorry for the delay - we had a school holiday.

    Relay agent isn't configured on our router, so I don't know what's causing it. I think I'll wait until the summer holidays and put everything onto one IP range, just to simplify the setup.

    Thanks for your help.

    Tuesday, June 6, 2017 2:00 PM
  • Hi Reinwood,

    Thanks for your updating.

    If there is anything else we can do for you, please feel free to post in the forum.

    Best Regards,

    Candy


    Please remember to mark the replies as answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.

    Wednesday, June 7, 2017 1:36 AM