Why are Android Devices showing up in my DHCP Address Leases

Posted on 2012-08-27
Last Modified: 2012-08-28
I have broken up our company network into a couple of VLans.  

1.  VLan-1 = 192.168.1.X = Administrative VLan and Misclaneous Device Vlan.
     a.  Switches and Electrical/HVac panels

2.  Servers VLan (not relevant here)

3.  VLan-21 = 10.220.21.X = Windows Domain PC receiving DHCP.
     a.  DHCP Scope .55 - 254 for DHCP.

3.  VLan-40 = 10.220.40.X = Wireless VLan = for Ipad and Wireless Cell phones (to receive email and internet).

My question is regarding our DHCP address.  DHCP is woring just fine and has been woring for 3-Plus years now.  However, I now have noticed that the Address leases (in teh VLan-21 DHCP SCope) are shwowing some android devices.  It is if these android devices are getting IP Addresses for my VLan-21 Network.  Please see screen shot.

My 1st question is why are these 'android' devices and 'Blank' devices showing up in the Address Leases?  Is it because someone is connecting a "rouge" wireless router to an active 'VLan-21' jack and giving out connections that way?

When I connect my android device to my company wireless network(VLan-40), I can see my cell phone's wi-fi MAC address in the VLan-40 address leases.  I do not see it in the VLan-21 address leases(that is what I would expect).  What do you think is going on?
Question by:Pkafkas
    LVL 20

    Accepted Solution

    >Is it because someone is connecting a "rouge" wireless router to an active 'VLan-21' jack and giving out connections that way?

    Short answer.  Probably yes.
    LVL 21

    Assisted Solution

    by:Joseph Moody
    You may want to look at this:

    Or you may want to use 802.1X to dynamically manage VLANs.

    Author Comment

    My suspisions and everyone else's in this thread are correct.  It was a rouge DHCP router that someone clicked the reset button and becasue of that it collected an IP address with DHCP and it gave out IP Addresses with DHCP (with no password).  

    There was 1 ehter net connection connected to the VLan-21 Vlan from teh rouge DHCP router.  That is where teh 192.168.1.X IP's were coming from.

    Very annoying.

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