[Sugar-devel] Notes on service discovery XS/XO
dr at jones.dk
Mon Apr 20 09:53:25 EDT 2009
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On Mon, Apr 20, 2009 at 07:26:30AM -0400, Benjamin M. Schwartz wrote:
>Martin Langhoff wrote:
>> The short of it is that mdns/dns-sd make sense for a small,
>> underutilised network of peers. They assume that the network is a
>> cheap resource, that broadcast messages are cheap, and that there is
>> no coordinating server.
>mDNS assumes all of the above things. DNS-SD does not. DNS-SD is
>perfectly happy to work on a standard DNS server. From the spec
> This document proposes no change to the structure of DNS messages,
> and no new operation codes, response codes, resource record types,
> or any other new DNS protocol values. This document simply specifies
> a convention for how existing resource record types can be named and
> structured to facilitate service discovery.
>I'm not particularly knowledgeable about the XS service discovery
>requirements, nor about DNS, so I can't reasonably tell you to use
> What I can say is that it seems like it should be workable.
DNS-SD using unicast DNS seems reasonable to me too.
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
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.
* Jonas Smedegaard - idealist og Internet-arkitekt
* Tlf.: +45 40843136 Website: http://dr.jones.dk/
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