[Users] SRV Lookups

Daryl Sanders daryl.sanders at gmail.com
Thu Nov 24 14:02:14 CET 2005


I think many of us just assume that if SRV queries are supported, then
the failover piece will work as well. I had the same experience with
Asterisk. It only only reads the first record.

- Daryl

On 11/24/05, Bogdan-Andrei Iancu <bogdan at voice-system.ro> wrote:
> 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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> >
>
>
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