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

perl-list perl-list at network1.net
Thu Jan 5 18:42:08 UTC 2017

Without the bit about not giving an IP (or an IP from a different subnet) if the relay is, you could do it something like this: 

shared-network SomeNetwork { 
subnet netmask { 
option routers; 
option subnet-mask; 
pool { 
subnet netmask { 

which alerts the DHCP server that requests from are in the same physical network as and so it will pick a pool address from - 

as for how to not answer when 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 and 3 dhcp relay. Each dhcp relay will use a
> loopback to relay the dhcp request or or The client
> machines will receive an IP in

> Is it possible ?

> NB: if there's a DHCP relay in, I don't want to offer an IP in

> Do you have a link or keywords that would help to find the typical configuration
> for that

> Thank you

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> dhcp-users at lists.isc.org
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