dhcp server testing programs

[Ed Ravin]

On Wed, Jan 11, 2012 at 12:05:36PM -0800, Paul B. Henson wrote:
> On Tue, Jan 10, 2012 at 11:59:40PM -0800, Christoph Pleger wrote:
> 
> > By the way, does anybody know about a DHCP client program that simply
> > retrieves information from the server and displays it (like bootpc
> > does), but does not try to configure things like IP address etc. locally
> > on the client machine and does not set itself to background?
> 
> dhcpcd (http://roy.marples.name/projects/dhcpcd/) supports a test mode:
> 
>      -T, --test
>              On receipt of DHCP messages just call
>              /lib64/dhcpcd/dhcpcd-run-hooks with the reason of TEST which
>              echos the DHCP variables found in the message to the console.
>              The interface configuration isn't touched and neither are any
>              configuration files.  To test INFORM the interface needs to be
>              configured with the desired address before starting dhcpcd.

What I need is a program that sends a DHCPDISCOVER and reports the
results, without actually getting a lease from the server or setting
up an IP address from the client.  The "dhclient -n" option is
documented as behaving fairly close to that, except when I tried
it with isc-dhclient-4.1.2 it turns out the "-n" option is silently
ignored.