[Dnsmasq-discuss] Multiple subnets without IP aliases

[Simon Kelley]

On 21/08/13 16:34, Brian Rak wrote:
> I have a layer 2 vlan (all hosts in the same broadcast domain), that has
> multiple subnets active on it.  For example:
>
> interface ve 906
>   ip address 10.0.5.113 255.255.255.248
>   ip address 10.0.6.105 255.255.255.248
>
>
> I have a machine with this configuration:
>
> br0      inet addr:10.0.6.110  Bcast:10.0.6.111 Mask:255.255.255.248
>
> I'd like to serve addresses from both subnets from this machine
>
> I've found that I can do this if the machine running DNSMasq has an IP
> address in both subnets, but this is somewhat of a waste of IP
> addresses.  Is it possible to serve DHCP to both subnets without having
> an IP address on the machine in both subnets?
>
> Before I added the IP alias, I was seeing this:
>
> dnsmasq-dhcp[5848]: 3598047279 available DHCP subnet:
> 10.0.6.104/255.255.255.248
>
> DNSMasq wasn't even seeing the other subnet as being available.
>
> Once I added the alias, it did work properly:
>
> dnsmasq-dhcp[5952]: 1867860253 available DHCP subnet:
> 10.0.5.112/255.255.255.248
> dnsmasq-dhcp[5952]: 1867860253 available DHCP subnet:
> 10.0.6.104/255.255.255.248
>
>
> Renumbering the network isn't an option.
>

Not possible, I'm afraid. It was an early design decision to require 
that dnsmasq (or a relay) have an local interface with an IP address on 
each subnet, to allow automagic association of dhcp-ranges with 
broadcast domains.

Cheers,

Simon.