[Dnsmasq-discuss] How small is a 'small network'?

Jonathan S. Fisher jonathan at springventuregroup.com
Tue Nov 17 01:00:49 GMT 2015


DnsMasq authors, please explain this better than I can... but here's my
understanding: The limit on number of clients on your network will be
bounded by DnsMasq's concurrency rate, not necessarily the sheer number of
clients. DnsMasq is single threaded and uses a simple select() fd_set loop (
http://daniel.haxx.se/docs/poll-vs-select.html) which means it takes a
bunch of file sockets in (I assume each UDP request is a socket) then it
processes them all and returns control to the OS. 1024 seems to be the
limit on linux, so I imagine once you approach that many concurrent
requests I imagine packets will simply be dropped since it's UDP.

With a network of 400 average business users, we see spikes to 200+ UDP
pps, steady state is around 70-80 pps.

On Mon, Nov 16, 2015 at 4:05 PM, Norman Gray <norman at astro.gla.ac.uk> wrote:

>
> Greetings.
>
> The dnsmasq documentation stresses that it's a good solution for 'small
> networks', but how small is small?  The overview seems to give as examples
> home networks, or mentions dnsmasq running in a router (implicitly a SOHO
> router).
>
> I have what I'd call a medium-sized network of machines to look after,
> which -- depending on how I/we organise the network -- could represent
> between 500 and 1000 machines.  I'd like to provide DHCP and caching DNS to
> a good fraction of them, and provide authoritative (intranet) records for
> perhaps half.  Dnsmasq looks like it would be very convenient to use for
> that, but would those numbers tax dnsmasq unduly?
>
> I would guess that DNS and DHCP wouldn't necessarily imply a huge load on
> a machine, but I'd guess also that the load would scale roughly with the
> square of the number of machines being served (or perhaps linearly both
> with the number of machines being served and with the number of
> authoritative local records).
>
> The machines are heterogenous in use, as opposed to being a compute farm,
> or something else which would suggest that cache hits would be unusually
> common.
>
> The manpage mentions that 'Dnsmasq is capable of handling DNS and DHCP for
> at least a thousand clients.'  That's about the number of clients I'm
> thinking of, so that's good, but is there a 'with ease' elided there, or a
> 'without overwhelming pain'?  Would I, in short, be storing up trouble for
> myself?
>
> I couldn't find discussion of this in a quick search of the list archives,
> but I wasn't really sure what best to search for.
>
> Thanks for any advice.
>
> Best wishes,
>
> Norman
>
>
> --
> Norman Gray  :  https://nxg.me.uk
> SUPA School of Physics and Astronomy, University of Glasgow, UK
>
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