What we've seen when doing the two PRI gateways as two separate unmanaged gateways is that if the first one in the list goes down, often the first couple of calls attempted don't work but it does seem to figure out what to do after that. Does sipX mark the gateway as "dead" and ignore it for a while? Or does it still try it for each and every outbound call? I guess most of my failover testing has been with failing the PSTN, as opposed to taking the actual gateway offline, which is to say that the AudioCodes gateway was still there to say "nope, sorry the PRI is down" as opposed to getting no response at all...
-Steve -----Original Message----- From: Dale Worley [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 22, 2008 11:56 AM To: [EMAIL PROTECTED] Cc: sipx-users Subject: Re: [sipx-users] Load balanced Gateways On Wed, 2008-10-22 at 08:27 +1000, Josh Marshall wrote: > My memory is a bit hazy, but when I was watching dns requests with > tcpdump when I first installed sipX (a few months back now) the sipX > server performs SRV lookups, and if they fail, perform A lookups. > > The thing I'm not certain of is whether the sipX will cache lookups / > choose a different gateway each time (I assume this is what you want by > load balance). I do believe that for high availability you're better to > put the two gateways in the config because if sipX fails connecting to > the gateway it will fail the call, rather than try the next gateway when > the DNS returns multiple results. sipX handles SRV records like it should. It can cache the DNS lookups, but even then, it does a proper randomization every time that it uses the DNS records to send a message to a destination. Having multiple gateways is a little more complicated. From SIP's point of view, a DNS name is a destination, and if DNS gives more than one address for it, those are alternative routes to the *same device*. So sipX will try each address in turn until it gets a response. If you have two gateways, and you put both their addresses onto one DNS name, sipX will try both addresses if it has to. If the first gateway is *down*, sipX will try the second gateway. But if the first gateway is *busy*, it will send a 486 (or some other failure response), and sipX, having gotten a response from "the device", won't attempt to contact "the device" using the second address. Unfortunately, fallback between redundant gateways is difficult to handle well in SIP. Dale _______________________________________________ sipx-users mailing list [email protected] List Archive: http://list.sipfoundry.org/archive/sipx-users Unsubscribe: http://list.sipfoundry.org/mailman/listinfo/sipx-users
