DHCP gives an IP when the DHCP relay is not in the subnet

[Bill Shirley]

Set up a class:
class "DHCP_relay_4" {
     match if (packet(24,4)) = 0a:01:01:04;        # 10.1.1.4
}

Then add to the pool definition:
pool {
   deny members of "DHCP_relay_4";
   range 192.168.1.2 192.168.1.254;
}


Bill

On 1/5/2017 1:42 PM, perl-list wrote:
> Without the bit about not giving an IP (or an IP from a different subnet) if the relay is 10.1.1.4, you could do it something 
> like this:
>
> shared-network SomeNetwork {
>   subnet 192.168.1.0 netmask 255.255.255.0 {
>     option routers 192.168.1.1;
>     option subnet-mask 255.255.255.0;
>     pool {
>       range 192.168.1.2 192.168.1.254;
>     }
>   }
>   subnet 10.1.1.0 netmask 255.255.255.0 {
>   }
> }
>
> which alerts the DHCP server that requests from 10.1.1.0/24 are in the same physical network as 192.168.1.0/24 and so it will 
> pick a pool address from 192.168.1.2 - 192.168.1.254
>
> as for how to not answer when 10.1.1.4 relays (or answer with a different subnet's IP), that is beyond my knowledge.
>
> --------------------------------------------------------------------------------------------------------------------------------
>
>     *From: *"Mik J" <mikydevel at yahoo.fr>
>     *To: *dhcp-users at lists.isc.org
>     *Sent: *Thursday, January 5, 2017 12:36:58 PM
>     *Subject: *DHCP gives an IP when the DHCP relay is not in the subnet
>
>     Hello,
>
>     Is it possible that the dhcp offers an IP but the dhcp relay is not in the subnet ?
>
>     I have a vlan 192.168.1.0/24 and 3 dhcp relay. Each dhcp relay will use a loopback to relay the dhcp request 10.1.1.1 or
>     10.1.1.2 or 10.1.1.3. The client machines will receive an IP in 192.168.1.0/24
>
>     Is it possible ?
>
>     NB: if there's a DHCP relay in 10.1.1.4, I don't want to offer an IP in 192.168.1.0/24
>
>     Do you have a link or keywords that would help to find the typical configuration for that
>
>     Thank you
>
>
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