[Dnsmasq-discuss] Multiple IP blocks on single ethernet segment

Simon Kelley simon at thekelleys.org.uk
Sat May 12 14:53:10 BST 2012

On 10/05/12 21:07, John Kinsella wrote:
> Guys - I've dug through the list archives and I haven't seen a clear answer
> to this, so excuse me if I'm repeating things.
> I'm running dnsmasq for DHCP services (as part of CloudStack). IP addresses
> are statically assigned via mac, defined in /etc/dhcphosts.txt. This all
> works perfectly fine for a single IP block.
> Until I try to assign IPs for another IP block, and then get
> May 10 01:28:49 dnsmasq-dhcp[1057]: no address range available for DHCP
> request via eth0
> Problem is, when I order IP blocks from my provider, they're routed to me
> via my VLAN. I have multiple /28s on this single Ethernet segment. I need
> dnsmasq to be able to answer DHCP requests to Ethernet addresses with IP
> addresses that are outside the network range of the listening interface.
> My understanding is this is a limitation in dnsmasq?
It is a limitation of dnsmasq to the extent that dnsmasq derives the 
relationship between IP ranges and network segments automatically, and 
it requires that the interfaces it's using has an address on the subnet 
it's assigning from to do that (with the exception of relays)
> On the DHCP side, I can't think of a technical limitation that causes this
> - DHCP is a layer 3 protocol, it doesn't care about IP ranges on
> interfaces. I'm presuming this limitation is in place because of the DNS
> caching side of the equation?

DHCP isn't pure layer 3, for an unconfigured client, the only thing 
known is the physical network segment on which the client exists. There 
has to be a way to get from that to an IP address. No DHCP server, as 
far a I know, allows arbitrary configuration of static IP addresses 
without some checks that the address assigned is on a subnet that the 
server knows about.
> If I'm completely wrong and dnsmasq (version 2.55) does support this, my
> apologies and I'd appreciate a pointer in the right direction.
It doesn't, sorry. The best suggestion might be to look at ISC dhcpd and 
the "shared network" keyword.



> John
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