[Users] SRV Lookups

Bogdan-Andrei Iancu bogdan at voice-system.ro
Thu Nov 24 12:56:54 CET 2005


Hi,

this problem (failover based on SRV) may  find a answer with the new 
serial forking support that I plan to add in core. See me post on devel:
    http://openser.org/pipermail/devel/2005-November/001184.html

regards,
bogdan


Mikael Magnusson wrote:

> Klaus Darilion wrote:
>
>> Douglas Garstang wrote:
>>
>>> All,
>>>
>>> I'm trying to get SRV lookups to work with OpenSER 1.0.0. I've
>>> exhausted every avenue of documentation including newsgroups, various
>>> forums etc.
>>>
>>> Using t_relay, OpenSER seems to be performing the correct DNS SRV
>>> queries and obtaining a list of hosts to try. Below are the relevant
>>> sections of my DNS zone file. We're  talking UDP, and based on the
>>> priority and weights below, OpenSER should be basically doing a
>>> round-robin approach, and it seems to be.
>>>
>>> The problem occurs when one of the hosts is not contactable. OpenSER
>>> simply stops and does not try the next host in it's list. I would
>>> have thought that for OpenSER to fully support SRV lookups, it should
>>> try each until it is successful. After all, that's a large part of
>>> the whole point of SRV records.
>>
>>
>>
>> (open)ser does not support SRV failover. It just looks for 
>> _sip._protocol and uses the first found record. No failover if there 
>> is a problem with the destination.
>>
>>> Does the t_relay() function have logic within itself to keep trying
>>> hosts until it gets a connection? What would be the definition a
>>
>>
>>
>> no
>>
>>> failure that would make it move onto the next host be anyway? Network
>>> failure certainly, but would a 'Not found' be considered a failure
>>> that would cause it to move on? Would anything other than an ACK be a
>>> failure?
>>
>>
>>
>> If you receive a SIP response, than there is no transport failure -> 
>> no failover to other SRV hosts.
>>
>
> The next SRV record should be tried if a 503 "Service Unavailable" SIP 
> response message is received, according to RFC3263 section 4.3.
>
> /Mikael
>
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