[Users] NEW FEATURE: DNS-based failover

Bogdan-Andrei Iancu bogdan at voice-system.ro
Thu Jan 25 17:04:35 CET 2007

Hi Christian,

note that as the DNS-based failover uses also the NAPTR records, the 
protocol may also change :). Of course, depends on your proxy settings 
(if tcp / tls is enabled).


Christian Schlatter wrote:

> That's very good news, this will definitely simplify our openser 
> config. I'll let you know once I've tested this new feature.
> I'm impressed,
> Christian
> Bogdan-Andrei Iancu wrote:
>> Hi everybody,
>> OpenSER 1.2.0 has now the capability to do DNS based failover, 
>> according to RFC3263 (http://www.ietf.org/rfc/rfc3263.txt).
>> The SIP resolver was enhanced to to be able to save and resume later 
>> the DNS queries in order to get all possible IP destinations. The 
>> resolving process is step-by-step done (get next IP only on demand) 
>> to minimize the total number of DNS queries. So having this support 
>> does not imply, in normal processing, more load on the DNS server. 
>> Additional queries are done only when needed (after failure detected).
>> The scanning for new IP destinations is done by the SIP resolver on 
>> all DNS levels: NAPTR, SRV, A.
>> Both core and TM are using this new feature.
>> In core, the stateless forwarding can do only DNS-based failover at 
>> transport level (if no egress interface found or send operation
>> failed due whatever reason).
>> In TM, the DNS-based failover is extended to transaction level. If 
>> the transaction completes with 503 or 408 with no reply, 
>> automatically, a new branch will be fork if any destination IP can be 
>> found by the DNS resolver.
>> Read more here http://www.openser.org/docs/modules/1.2.x/tm.html#AEN103
>> For controlling this feature use:
>>     - newly added core parameter "disable_dns_failover" - use to 
>> generally disable the DNS-based failover. By default is false.
>>     - in TM, t_relay() take a new flag for turning off the DNS-based 
>> failover. This setting is per transaction. By default, the failover 
>> is done.
>> Any feedback is appreciated.
>> regards,
>> Bogdan
>> _______________________________________________
>> Users mailing list
>> Users at openser.org
>> http://openser.org/cgi-bin/mailman/listinfo/users
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