[JDEV] Service name in SRV records

[Ralph Siemsen]

matthew c. mead wrote:

> So for my (and hopefully the list's) benefit, can you provide a
> description of all the SRV record data supported by jabber
> servers and clients?  I don't quite understand what all the
> numerical data included means.

You mean the numbers that come back in the SRV lookup? These are defined 
in RFC 2782, see for example http://rfc.sunsite.dk/rfc/rfc2782.html.

Basically, SRV lookups are a bit like finding a mailserver.  You do the 
query and instead of getting back _one_ IP address, you might get 
several of them.  There is a simple process for deciding which of them 
to pick: each result has a "priority" and a "weight" factor.  You try 
the highest priority first.  In case of ties for priority, you try them 
essentially randomly, but weighted by the factor.

For most jabber servers there will be only one entry, so the priority 
and weighting is overkill, but its a reasonable standard and pretty easy 
to implement.

One other difference: normally DNS lookups are just used to resolve name 
to IP, the port number is not considered.  But SRV records tell you 
which port to connect on.  Think of an SRV query as asking "tell me how 
to reach the jabber service on host mycooldomain.com".

Hope this helps
-Ralph