[Dnsmasq-discuss] DHCP ranges for 'supernetting'

[Simon Kelley]

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On 11/02/15 14:15, Jim Alles wrote:
> I have been contemplating this issue for some time, yet with
> minimal testing and no code-reading.
> 
> I have searched on several terms at 
> https://www.mail-archive.com/dnsmasq-discuss@lists.thekelleys.org.uk
> along with the man pages & the example.conf and got a general idea
> that my impression might be true.
> 
> The hypothesis: Given a standard class C subnet of 192.168.2.0/24
> and having outgrown it, I change my linux-based router to
> 192.168.2.0/23 (supernet two Class Cs). Due to the initial
> selection there are no surprises with the block range beginning
> address shifting, the broadcast address gets pushed out to 
> 192.168.3.255
> 
> I change my DHCP range to 192.168.2.100 -- 192.168.3.254.
> 
> dnsmasq seems to hand out DHCP address between 192.168.2.100 to 
> 192.168.2.254, but nothing in the 192.168.3.x block, unless I add a
> second dhcp-range statement for 192.168.3.1 -- 192.168.3.254, which
> does work as intended.
> 
> Is this expected behavior?

I'd expect dnsmasq to start using the larger range, but observe that
both DHCP clients and servers try very hard not change the address of
any machines that already have an address, or ever had one in the
past, so it's quite possible that you wouldn't see the new range used
for machines which are brand-new to the network, as long as there is
some space available in the old range.

Is dnsmasq sending the correct (255.255.254.0) netmask to clients?


Cheers,

Simon.


> Is it also true for changing subnets in the class A & B RFC1918
> address spaces?
> 
> Thanks for your consideration.
> 
> Jim Alles
> 
> 
> 
> _______________________________________________ Dnsmasq-discuss
> mailing list Dnsmasq-discuss at lists.thekelleys.org.uk 
> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
> 
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