[Dnsmasq-discuss] Overlapping/duplicate subnets
rob0 at gmx.co.uk
Wed Feb 22 15:07:20 GMT 2017
On Wed, Feb 22, 2017 at 02:55:30PM +0100, S. M. Hossein Hamidi wrote:
> I am new to dnsmasq and my mind is busy with a DHCP scenario that I
> would like to consult with you before getting my hands dirty.
> Suppose that we have several subnets which are behind a NAT device
> which additionally acts as a DHCP relay agent. I know that using
> DHCP relay agent information option, I can distinguish between
> different subnets. However, the additional constraint is to use
> duplicate or overlapping subnets instead of distinct subnets.
That is a very strange constraint. RFC 1918 is quite large enough;
it's not necessary to share your netblocks. And how will your NAT
device distinguish one segment with a shared netblock from another
segment using the same netblock?
Sounds like broken IP networking to me. Compliant IP stacks do
routing based on IP address blocks.
> Since, the traffic comes from each segment goes through NAT, it
> wouldn't be any problem to use duplicate IP addresses, knowing
> that each segment has its own autonomy.
But again, how does the NAT device do this?
> So, may I know if can I exploit tagging feature of dnsmasq so
> that it can handle separate potentially overlapping leases for
> each subnet?
I'm pretty sure this would not be possible in dnsmasq nor in ISC
dhcpd. Either one could do a single netblock shared among many
distinct segments, but each would only be able to give out any one
address to only one client.
But wait and see what Simon says. :)
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