dhcpcd-discuss

On 2011-12-09 20:59, Roy Marples wrote:
> Hi
>
> On Wed, 2011-12-07 at 15:26 +0100, Egil Hjelmeland wrote:
> > I want to be able to send a DHCP INFORM to request application
> > settings, independent of the network handling. The idea is allow
> > application settings to be served from a different DHCP server than
> > the one serving the network settings. It seems to me that it can not
> > be done with dhcpcd?
> >
> > What I would like to have is an option to dhcpcd which makes it send a
> > DHCP INFORM, call specified script for each DHCP ACK, and exit after
> > specified timeout. Don't touch any configuration. Don't interfere with
> > main dhcpcd operation.
> >
> > Would that be possible to make? Or do you know of other lightweight
> > tools that could do that for me?
> So on the same interface there are two DHCP servers, one handling
> network config and the other handling application settings? I am
> actually curious as to why this even sane network config or even
> desired?
>
> Well, we could add an option to broadcast INFORM at various intervals
> and run the script for each ACK and then timeout. Would that work for
> you?
>
> Thanks
>
> Roy
The use case is SIP phones and a SIP PBX. I want to use DHCP to 
provision the SIP server address to the phone (+plus possibly a http url 
for phone config). To make it easy for customers, I want to run a DHCP 
server in the SIP PBX to provide the SIP server address for the local 
network. But in many cases I anticipate that the customer has some other 
DHCP server which leases addresses. To minimize support calls due to 
conflicting DHCP servers, my idea is that by default, the SIP PBX only 
answer on DHCP INFORM. That I can do with dnsmasq. The SIP phone runs a 
DHCP(cd) client as a deamon. If the DHCP ACK leasing an address did not 
contain a SIP server address, the phone can try an DHCP INFORM to get 
the SIP server address (from the SIP PBX).

So what I had in mind was that you can invoke dhcpcd as a command to 
send DHCP INFORM and collect answers within a timeout, while the main 
dhcpcd deamon is still running. The ultimate would be if the second 
dhcpcd told the deamon dhcpcd to do the job, in order to avoid conflicts 
over port 68.

In the mean time, I have realised that sending DHCP INFORM and 
collecting DHCP ACK is not rocket science, much more simple than 
handling statefull leases. So I am 2/3 on the way of making my own 
little code which does the query I need. Thankfully, I have noticed that 
dhcpcd don't bind port 68 more than it needs. But yes, it would be great 
if you put something like that on the roadmap.

Best regards
Egil