[Users] Re: [Devel] NEW FEATURE: DNS-based failover

[Bogdan-Andrei Iancu]

Hi Klaus,

yes, that is more than correct. You example points out exactly what I 
was warning Christian of  - during DNS-based failover, the used protocol 
may changes, based on the DNS records and proxy configuration.

regards,
Bogdan

Klaus Darilion wrote:

> Hi Bogdan!
>
> Good news. How are the DNS lookups done in detail? E.g. the following 
> setup:
>
> t_relay to domain.com:
>
> @domain.com
>      NAPTR   90 50 "s" "SIP+D2T" "" _sip._tcp.domain.com.
>      NAPTR   100 50 "s" "SIP+D2U" "" _sip._udp.domain.com.
>
> @_sip._tcp.domain.com.
>      SRV     0 0 6060 sip1.domain.com.
>      SRV     1 10 6060 sip2.domain.com.
>
> @_sip._udp.domain.com.
>      SRV     0 0 6060 sip1.domain.com.
>      SRV     1 10 6060 sip4.domain.com.
>
> sip1.domain.com   A   1.2.3.4
>
> sip2.domain.com   A   2.2.3.4
> sip2.domain.com   A   2.2.3.5
>
> sip4.domain.com   A   4.2.3.4
>
>
> Is the following assumption correct?
>
> 1. lookup NAPTR domain.com
> 2. lookup SRV _sip._tcp.domain.com
> 3. lookup A sip1.domain.com
> 4. request to 1.2.3.4; if failure
> 5. lookup A sip2.domain.com
> 6. request to 2.2.3.4; if failure
> 7. request to 2.2.3.5; if failure
>
> 8. lookup SRV _sip._udp.domain.com
> 9. (sip1 cached) send request to 1.2.3.4; if failure
> 10. lookup A sip4.domain.com
> 11 request to 4.2.3.4; if failure
> 12 reply error
>
>
> regards
> klaus
>
>
>
> 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
>>
>> _______________________________________________
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>> Devel at openser.org
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>
>
>