[Dnsmasq-discuss] Multiple server interaction with multiple subnets

Simon Kelley simon at thekelleys.org.uk
Wed Dec 6 08:07:19 GMT 2006


Data Control Systems - Mike Elkevizth wrote:
> Hi,
> 
> I have recently scrapped my Bind/DHCPd installation after a server crashed
> and not wanting to go through all the trouble setting up the new one. All
> seems to work well except that I can not figure out how to get one server
> running dnsmasq to return an address from another. I have one domain
> comprised of three subnets connected through a VPN. I would like to have
> each server be able to return all the addresses that all the servers have
> assigned via DHCP. For instance if server A assigns workstation Z an address
> and server B assigns workstation Y an address, I would like server A or B to
> be able to respond to a dns query for either workstation Y or Z. I'm sure
> this should be able to be done through forwarding, but I can't figure out
> how to make dnsmasq forward the requests and then respond properly. I tried
> just adding the all the dnsmasq servers to all the workstations as dns
> servers, but the local server must be responding with something which makes
> the workstation not use the other server. I'm sure I just have an option
> setup wrong, but If anyone could help point it out, I would be very
> appreciative.
> 

It is possible to configure multiple instances of dnsmasq the way you 
want, but it's probably not the best way to achieve the global goal. 
It's much better to have _one_ instance of dnsmasq and let it handle 
DHCP and DNS for all three subnets. If you have a machine which has 
interfaces on all three subnets then this is very easy: just provide 
dnsmasq with three "dhcp-range" options, one for each network. It will 
do everything else automagically.

If all three networks _don't_ meet on one router, then you will need to 
run a DHCP-helper on the ones which are remote from dnsmasq. Real IP 
routers (CISCO etc) normally have this facility. or you can use the ISC 
DHCP-relay, or DHCP-helper

http://www.thekelleys.org.uk/dhcp-helper

Just run the helper on a machine with an interface on the network in 
question, and tell the helper to send DHCP requests to the machine 
running dnsmasq.


HTH

Simon.



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