[Dnsmasq-discuss] dnsmasq and multicast (

Simon Kelley simon at thekelleys.org.uk
Thu May 10 17:39:47 BST 2012

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?

> 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.
> 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.



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