How can I forbid access to customer that force their IP to static ...

Simon Hobson dhcp1 at
Sat Jul 7 07:15:05 UTC 2007

Sébastien CRAMATTE wrote:

>How can I forbid access to customer that force their IP to static ...
>Some customers change their windows property and force the IP as
>be a static one ...
>I would like to prevent this ...
>Does it exists a feature inside dhcpd to do this ?

You cannot do this with DHCP.

You will have to find/write some software that will do it outside of DHCP.

I vaguely recall a description from someone on 
this list some time ago of the setup they used :

Software interrogates DHCP for leases - you can 
read the leases file, or the "on commit" function 
may be useful. This might have been combined with 
a registration system, I can't recall now (try 
looking at Netreg and see what that does).

Once you have a list of addresses that SHOULD be 
in use, you can compare the traffic seen on the 
network with this list and flag up any rogue IPs.

Using SNMP (or whatever you prefer), you can 
track down which switch port the device is 
connected to, turn it off, send alert to admins, 

You possibly want to be monitoring what port(s) a 
device is connected to anyway in a public network 
so that you have an audit trail of "who was 
where" if you get complaints about one of your 
customers - the "one of your customers at a.b.c.d 
( is | was ) ( port scanning me | brute force 
pass attacking me | DOSing me | killing my DNS 
server with queries | whatever)" type complaints.

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