Running new dhcpd instance on same physical interface

Dario Aguilar daguilar at
Tue Mar 17 13:16:01 UTC 2009

Thanks you all for the help, I don´t have any intention to break any RFC or
best practice or simply my head on a non-scalable solution so by the moment
I will configure an unique dhcpd instance. But, I´m agree with Steinar that
it would be nice to have a little custom solution for unicast only traffic.

Best regards,

Dario Aguilar.

-----Mensaje original-----
De: dhcp-users-bounces at
[mailto:dhcp-users-bounces at] En nombre de David W. Hankins
Enviado el: Lunes, 16 de Marzo de 2009 08:48 p.m.
Para: Users of ISC DHCP
Asunto: Re: Running new dhcpd instance on same physical interface

On Sun, Mar 15, 2009 at 12:08:46AM -0500, Frank Bulk wrote:
> It would be atypical for a service provider to run a separate instance 
> of DHCP for each type of service.

It is.

But I don't remember seeing this part of the thread before, so I wanted to
make a quick reply to this part;

> I will appreciate very much if you have a better idea or another 
> suggestion on how to resolve this without adding another physical 
> interface that in fact it will be connected to the subnet that the other

Provided all of the server activity is IP unicast, there is a (seldom used,
often broken, and poorly documented) way to build the DHCP server to
"USE_SOCKETS" (#define in includes/site.h).  With this build method, the
server can not be guaranteed to be RFC 2131 compliant in messages it can
receive or transmit (raw sockets work around that for us).

But, provided USE_SOCKETS was used, the "local-address" configuration
parameter becomes available, so the single dhcpd instance may be bound (as
through the bind() system call) to a specific IPv4 address, possibly an
alias address.  Take care to also configure the server's server-identifier
option identically.

In this manner, a single box can house any number of DHCPv4 server instances
differentiated by IPv4 addresses.

I can't go into any greater detail than that, so good luck.

David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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