[Dnsmasq-discuss] Feature request: make dnsmasq able to work as a proxydhcp

[Simon Kelley]

Guilherme Moro wrote:
> Hello all,
> 
> I have made a proxyDHCP server to my company, and I think  I can help to 
> implement this.
> 
> Unfortunately I dont have the permission to share my code ( that is 
> written in python ) but I think that can be pretty easy to make one 
> based on the dnsmasq code.
> 
> The spec is indeed a bit unclear. but after some packet sniffing of 
> other (closed source )ProxyDHCP server I have figured out what happens.
> Let me try to explain.
> 
> There are two scenarios:
> - the proxyDHCP server can run on the same machine that the DHCP server 
> are running
> - the proxyDHCP can stay in different machine that the DHCP server
> 
> for the first scenario we have the Proxy DHCP listening just in the 4011 
> port, but I need some kind of control of DHCP server, because the server 
> must respond "PXEClient" in the class identifier, so, when the client 
> see the PXEClient identifier, but no boot information, it request 
> (DHCPREQUEST) this information in the 4011 port.
> 
> the second scenario, we have the proxyDHCP running alone in other 
> machine of the network. In this scenario we make the server runs in the 
> 67 and 4011 ports . It will receive the DISCOVER in the 67 port, and 
> reply with a OFFER with the PXEClient class-identifier, and no ip 
> address ( 0.0.0.0 ), the client will just store the server IP address, 
> it will continue the normal DHCP process to get an IP address from the 
> DHCP server, and then, the client will make a DHCPREQUEST in the stored 
> IP, port 4011, to get the boot information.
> 
> If its still not so clear, its just ask for more clarifications, I'll be 
> happy to help. =)
> and let me know how to help you to code, if you want.
> 
> About the use of this kind of stuff, I see more and more people using 
> this kind of router/firewall/gateway hardware to setup remotely managed 
> networks ( see SonicWall for some example of hardware - 
> http://www.sonicwall.com/us/ ), and a lot of people dont even know about 
> proxyDHCP, and how it works, and like was said, theres no open source 
> server available (yet!) so people prefer to use other kind of setup to 
> achieve the same functionality.
> So this kind of support to boot will be a good thing, for a lot of 
> people, more than we can imagine right now
> 
> Regards,
> 
> Guilherme Moro

Many thanks, Guilherme, that is very useful information.

I guess it needs two configuration options, one to turn on port 4011, 
and one to enable the "reply with address 0.0.0.0 to PXE discover". None 
of that is a significant amount of code.

There should be tags set to tailor behavior in these two cases.

The other thing to worry about is sending the PXE DHCP options. As far 
as I can see, they are all sent as option 43 encapsulated vendor 
options, and dnsmasq supports those, which is good. The data formats of 
some of the options (things like the menu) are pretty complex, and not 
possible to produce with the existing --dhcp-option parsing code, except 
by entering them as pure hex. It probably makes sense to add some 
parsing code for that. Opinions on which options are used in real life 
and which can be ignored would be valuable.


Cheers,

Simon.