[Users] Best practice for DNS failover using OpenSER?

Klaus Darilion klaus.mailinglists at pernau.at
Thu Jan 11 17:31:43 CET 2007

openser does not support DNS based failover (nor NAPTR nor SRV nur 
multiple A records).

with openser you have to use the dispatcher module for this. you might 
also try ser CVS which has DNS based failover - but I have not tried it yet.


Kerker Staffan wrote:
> Hi
> I'm trying to get something to work that I thought should work
> out of the box, but when implemented didn't work the way I thought
> it would... Please comment.
> I'm using OpenSER as a core SIP proxy, among other things to connect
> to a POTS network via two independent Cisco PGW2200 SS7 GW. These
> gateways have fully DNS resolvable SIP domains (rfc 3263, NAPTR, SRV and A records).
> NAPTR (udp only) => SRV (udp only) => 2x A records (one for each redundant GW). Calls
> directed to POTS nicely load shares between the two A records. So far so good. 
> 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). 
> I would love some best practice implementation clues regarding OpenSER and multiple
> GW fail over, if anyone of you have such knowledge or experience. 
> Best regards,
> /Staffan
> ---
> Staffan Kerker, 
> Saab Communication
> Ljungadalsgatan 2, 35180 Växjö, Sweden
> p. +46 470 42185
> c. +46 705 391365
> m. staffan.kerker at saabgroup.com
> w. http://www.saabgroup.com 
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Klaus Darilion

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