[Sugar-devel] Notes on service discovery XS/XO
dr at jones.dk
Mon Apr 20 12:56:28 EDT 2009
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On Mon, Apr 20, 2009 at 04:08:30PM +0200, Martin Langhoff wrote:
>On Mon, Apr 20, 2009 at 3:53 PM, Jonas Smedegaard <dr at jones.dk> wrote:
>> DNS-SD using unicast DNS seems reasonable to me too.
>If we can do without the avahi gunk, and use it in a way that is not
>optimised for user driven browsing but for automated selection of
>services, then it might work.
>> Looking closer at the RFC, the initial service queries do have an
>> added overhead in that a layer of indirection is used (not SRV -> A,
>> but instead PTR -> SRV + TXT -> A). But standard DNS optimizations
>> apply, so SOA record should allow clients to preserve bandwidth
>> through caching.
>Can we teach dnsmasq to push all the relevant records with the SOA
I don't understand your question. Sounds like prefetching that isn't
part of dns (id you perhaps think of DHCP here?)
As I understand dns, if you request a SOA record, then you get a SOA
record and only that. You can request the whole domain, but that does
not seem bandwidth saving to me.
The main bandwidth saver, I believe, is that of sane query caching and
knowledge of the segments of the domain structure.
>> In other words: Install dnsmasq on the XOs, use plain standard DNS
>> internally and on the wire, setup DNS-SD entries in a standard
>> nameserver on the XS, and extend Sugar to support DNS-SD.
>> I'd be happy to help compose standard BIND9 files, if that is what
>> will be used on the XS.
>If we have a dnsmasq resident expert, I rather use your help
>transitioning to dnsmasq (note - with several bits of weird dhcp
>rules). There is no upside to BIND and plenty of downsides, starting
>with the >25MB memory footprint.
If that's me you titulate so nicely, then you are way too kind:
I have only little experience with dnsmasq used as a caching-only name
server, i.e. zero experience with dnsmasq as a "real" name server
containing local data.
You are right that BIND9 is a bastard with memory consumption, and it
makes sense to use dnsmasq on the XS. I just didn't think of that - I
suggested it as a caching-only on the XOs. ISC DHCPd has a complex
macro language, however, which might be the upsight you cannot live
without. Beware that it is DHCP, not DNS ;-)
It seems from its changelog that dnsmasq supports DNS-SD since version
Tell me more specifically what you fear can be tricky to handle in
dnsmasq, either DHCP or DNS parts, and I shall have a look if I am any
good at helping out.
* Jonas Smedegaard - idealist og Internet-arkitekt
* Tlf.: +45 40843136 Website: http://dr.jones.dk/
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