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
