[Dnsmasq-discuss] dnsmasq and multicast (

David Dombrowsky david.dombrowsky at redlion.net
Fri May 11 14:23:42 BST 2012

On 05/10/2012 12:39 PM, Simon Kelley wrote:
> On 09/05/12 21:00, David Dombrowsky wrote:
>> Please forgive the newbie question.
>> Is there anything in dnsmasq which implements listening on a
>> multicast address?
> No.
>> The IANA address allocation does say that
>> is a standard DHCP server address, on which I assume DHCP
>> servers can listen.
> That's a new one for me: do you have a reference to any standard for
> that?


> DHCP for IPv6 uses multicast, but it's possible there because hosts
> can assign themselves a link-local address before attempting DHCP.
> In the IPv4 world that's not possible and various nasty hacks are
> used to bootstrap things.
>> First: is this even a responsibility of this application layer of
>> the stack, or is it supposed to be implemented in kernel or network
>> configuration?
> I don't know. I imagine a standard document would tell us.

The interwebs don't really seem to help reveal how this multicast
addressed is used and how it relates to DHCP servers.  It seems to
be a mystery.

>> Second: the end goal is to have multiple dnsmasq-based DHCP servers
>> listening on not-well-known IP addresses on the network.  Also, the
>> servers should only receive requests from a proprietary relay agent,
>> which won't know the IP address of the DHCP servers.  I think
>> multicast is the way to solve this, but I'm not positive.  Any ideas?
> It's well out of the usual use-case. Why do you want multiple
> servers. for availability? If so, be aware that dnsmasq doesn't
> implement the DHCP failover protocol, and the ISC server may be a
> better choice.

We need two servers to avoid the single point of failure problem.
The servers really don't need any failover protocol, because all the
addresses are statically assigned anyway.

David Dombrowsky, Software Engineer
Sixnet, a Red Lion business | www.sixnet.com
+1 (518) 877‐5173 x161 office

More information about the Dnsmasq-discuss mailing list