[VoIP] ENUM Round Robin DNS?

[Mark Rudholm]

Greg Blakely wrote:
>  
> 
>> What is CNET using for ENUM DNS service presently?
>> More than one DNS server?
>>
> Usually 4 servers:  one at my work, one at home, and two at
> backupdns.com.
> 
> Currently, the two at backupdns.com have corrupt records, so I have
> dropped them for now.  As soon as I get that squared away, they'll be
> back.
> 
> If anyone wants to 'secondary' the zone, let me know off-list, and we'll
> work out the details.
> 
> As to multiple NAPTR records, Mark is correct:  we can make multiple
> entries.  I'll have to re-read my BIND documentation, but I believe that
> the 'named' server will respond with all records, if the querying end is
> capable of accepting more than one record, and responds in a round-robin
> method to those querying clients that are capable of accepting only one
> result.
> 
> Can anyone confirm or debunk this?

Sure.

The general case is that DNS does support multiple records
per resolved domain, as in your multiple A record example.

All records for a given query are returned to the querier
in all cases.

They are not returned in any order, they are returned as
an unordered set.  The decision about which to use is left
to the client if one must be selected.

Now, NAPTR records, like MX records, include a field for
priority, so this means the DNS database gives the client
instructions about which server to try first.

This provides *network* redundancy, but not necessarily
*application* redundancy.  For example, if I get two MX
records for ckts.com and I try to send email to
user at ckts.com via one of the MX records and that server
tells me "user unknown" my mail will come back undelivered,
as my MTA will not try the other MX record to see if "user"
exists on the other server.

-Mark