Interference between multiple DHCP instances on the same server

Abu Abdulla alhanbali montaqa at
Thu Apr 29 06:00:09 UTC 2010

yes the two IPs are in the same vlan (two different phyiscal
interfaces). actually i need this because the firewall port is open
for only one ip. i will try to look at the OS level if i can bind the
dhcp process with specific IP.

i noticed something (i don't know if it is related to a miss
configuration in my setup or not); i have the same pool configured in
the two instances but with different options, the request came to one
instance but the response came from the other dhcp instance through
the other IP (default IP). i removed the pool from the other instance
and it starts working giving the correct options. i really don't know
what happened at that time since i was trying many things at the same
time. in addition one instance is using a compiled version with
USE_SOCKETS support and the other one is not. i was monitoring the
traffic using the firewall/snoop and the test STB box in the test

On Thu, Apr 29, 2010 at 8:47 AM, Glenn Satchell
<glenn.satchell at> wrote:
> If the two interfaces are on the same subnet it shouldn't matter which
> interface they send their responses out. This is a function of the kernel's
> network stack and is outside the control of dhcpd.
> Use of server-identifier should tell the clients to send their response back
> to that particular server ip, rather than the source IP of the packet. I
> would assume that you have different IPs on the two interfaces.
> Apart from observing the traffic, are there any errors reported, or dhcpd
> not functioning correctly?
> regards,
> -glenn
> On 04/28/10 20:55, Abu Abdulla alhanbali wrote:
>> Hi,
>> I have installed additional DHCP instance on the same physical machine
>> (different interface) that has another DHCP.
>> I’m binding each server with the interface at the startup: dhcpd
>> <options>  <interface>
>> On the other hand, I’m noticing strange behavior:
>> The second server is receiving the request from the correct interface
>> but the response is sent from the other interface. I checked this by
>> ‘snoop’ the two interfaces. I tried also compiling the server
>> (solaris) with USE_SOCKETS support (even though it is designed for
>> another purpose) and define local-address / server-identifier without
>> success.
>> Any hint where could be the problem.
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