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How to avoid rogue DHCP servers?

Posted on 2014-01-27
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Last Modified: 2014-01-28
Hi,

I had a DHCP problem in my network right now and the reason was that someone had plugged in his private Wifi router that started giving out IP address from its own range ...

How could I prevent (on a technical level) something like this happening again?

(Windows 2008 Domain)

Thank you!
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Question by:Xeronimo
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Expert Comment

by:Paul 1
ID: 39811642
The non-tech way is better, when you find the device disable it with a hammer!

here is the other way
http://technet.microsoft.com/en-us/library/cc754792.aspx
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by:Xeronimo
ID: 39811663
Haha, yes!

As for authorization, my DHCP server (who's also a DC) has been authorized though ... and doesn't your link there only refer to DHCP servers that run on Windows servers? In my case it was a wifi router that started attributing IP addresses ... how would I prevent it from doing this?
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by:cwstad2
ID: 39811664
Are you able to configure you network switches to block DHCP on all ports except that of the server?
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Author Comment

by:Xeronimo
ID: 39811667
cwstad: I guess I should be able to do that, it's a HP ProCurve. But if not yet done something like that ... Is it similar to restricting traffic on firewalls?
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by:cwstad2
ID: 39811677
I doubt if you can on that model. Our network guys have configured on CISCO equipment.
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by:Xeronimo
ID: 39811713
Ok, I'll see what I can do!
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by:Miftaul
ID: 39811960
If you use cisco switches, configure dhcp snooping on switchports to stop rogue dhcp servers.
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Expert Comment

by:TimotiSt
ID: 39812214
If you can post the exact model of your switch, I can check if it supports DHCP snooping.

Tamas
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Author Comment

by:Xeronimo
ID: 39812240
Hi, it's a HP ProCurve 4240vl

Thanks!
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cwstad2 earned 250 total points
ID: 39812269
Take a look here. Worth a try. We have a couple in IT but only for desktop Switches

http://integratingit.wordpress.com/2012/08/13/configuring-dhcp-snooping-on-hp-procurve-switches/
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Assisted Solution

by:TimotiSt
TimotiSt earned 250 total points
ID: 39812366
That's good, the 4200vl series supports DHCP snooping since firmware L.10.09.

Config example from a 3400 series box:
dhcp-snooping
no dhcp-snooping option 82
no dhcp-snooping verify mac
dhcp-snooping vlan 23 
!
interface 47
   mdix-mode mdix
   exit
interface 48
   mdix-mode mdix
   exit
interface 49
   dhcp-snooping trust
   exit
interface Trk4
   dhcp-snooping trust
   exit

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