[Users] Best practice for DNS failover using OpenSER?

[Greg Fausak]

Jiri,

Thanks for the pointer!  I think I'll have to give this a look.
We are having specific problems with the DNS resolver on failover  
(when one
DNS resolver is not reachable, the next is queried, and openser is  
not acting
predictably when this happens).  It is as if the tm module is not
properly threaded.  Like when one thread gets stuck waiting for
a response from DNS resolver, another thread picks up a retry
SIP message and doesn't know about the retry in process!

We see the bad resolver behavior when 2 resolvers are listed in /etc/ 
resolv.conf, and
we turn off the first one.

The DNS failover is also interesting.  I think failover applies to A  
records
and SRV records (not NAPTR records).

-g

On Jan 16, 2007, at 7:12 AM, Jiri Kuthan wrote:

> indeed, the stuff is not well linked, we are working on it. Here  
> you go.
> http://cvs.berlios.de/cgi-bin/viewcvs.cgi/ser/sip_router/doc/ 
> dns.txt?rev=HEAD&content-type=text/vnd.viewcvs-markup
>
> -jiri
>
> At 02:46 16/01/2007, T.R.  Missner wrote:
>> Greg,
>>
>> This is a ref to SER. Apparently this functionality has been added  
>> to the new pre-release version. I did find some talk about it in  
>> the release notes.
>> I couldn’t find any specific documentation. Admittedly I don’t  
>> understand the layout of SER’s site very well as I haven’t spent  
>> much time there.
>>
>> -- TR
>>
>>
>> On 1/15/07 8:33 PM, "Greg Fausak" <lgfausak at gmail.com> wrote:
>>
>> In the text below I quote Kerker 'SER does support DNS failover.'.
>> Is this ser or openser?  Where can I read more about this?
>>
>> -g
>>
>> On Jan 15, 2007, at 10:40 AM, Klaus Darilion wrote:
>>
>>
>> Staffan,
>>
>>
>>
>>
>>
>> Kerker Staffan wrote:
>>
>>
>> ...
>>
>>
>>
>>
>> Now, if I disable one of the Gateways, I hang every second call.  
>> OpenSER does
>>
>>
>> not
>>
>>
>> try the second A record address if the first doesn't answer. How  
>> can I solve
>>
>>
>> this? Shouldn't OpenSER fail over to the second A record listed in  
>> the NAPTR
>>
>>
>> => SRV
>>
>>
>> resolving? Or will OpenSER continue to resend all SIP INVITES  
>> until timers
>>
>>
>> fire? Would
>>
>>
>> it help if the proxy recieved an ICMP port/destination unreachable  
>> from the
>>
>>
>> network? Is
>>
>>
>> there anyway to get around this? In the other direction, from POTS  
>> to sip,
>>
>>
>> the PGW2200
>>
>>
>> nicely switches over to the second of my two OpenSER servers if I  
>> shut one of
>>
>>
>> them down. These servers have the same DNS entries (but for  
>> another SIP domain, NAPTR =>
>>
>>
>> SRV => 2x A record).
>>
>>
>>
>>
>> Yes, OpenSER or for that matter every transaction stateful proxy  
>> should
>>
>>
>> do RFC 3263 based fail-over. But as you can imagine this is pretty
>>
>>
>> complex to implement and that's why openser does not support it  
>> yet, it
>>
>>
>> is listed on the development roadmap. The newest release of SER does
>>
>>
>> support DNS failover.
>>
>>
>>
>>
>>
>>
>>
>>
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>>
>>
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>
> --
> Jiri Kuthan            http://iptel.org/~jiri/
>