asterisk users - Mar 2008 - DNS Changes never picked up with Asterisk 1.4.18 chan_sip?

Hello,

We're attempting to use Asterisk for distributing calls via SIP in a
large-scale speech recognition/VXML environment.  We currently use DNS SRV
with weights and priorities to instruct VoIP gateways (not Asterisk) to
route calls to pools of servers.  This works extremely well and provides for
load balancing, fail-over, and by setting the TTL low (several minutes) we
can easily take machines out of service for maintenance just by adjusting
the appropriate DNS SRV records.  For business reasons, we now need to
achieve a similar setup using Asterisk instances hosted by a partner of
ours.

We've done a lot of reading on Asterisk and based on that our current
understanding is:

- chan_sip DOES now process DNS SRV weights and priorities (as of 1.4.X) but
only uses the first record (but correctly sorted by priority & weight)
- chan_sip DOES NOT use the dnsmgr for caching/update of DNS records
- Asterisk in general DOES NOT respect DNS TTL values (unclear if that was
addressed in recent versions)

In testing Asterisk 1.4.18, we are running into an even more basic issue --
changes to a host in DNS (with a single DNS SRV record) are never picked up
by Asterisk.  Our simple test scenario is:

- Set SRV record in DNS for hostname X to point to server foo
- Place calls and observe that Asterisk correctly routes call to server foo
- Update SRV record in DNS for hostname X to point to server bar (with TTL
of hostname X originally set to 5 minutes)
- Subsequent calls still go to the original server foo, even after waiting
hours or even days

Asterisk never seems to pick up the changed DNS info.

There are vague references on the web to being able to configure Asterisk
with DNS related settings. ("Unless specifically configured, Asterisk
1.2does not honor DNS Time To Live (TTL)." from
*http://tinyurl.com/2ossv6) *We've tried doing:

[dnsmgr.conf]
enable=yes            ; enable creation of managed DNS lookups
refreshinterval=300  ; refresh managed DNS lookups every <n> seconds

But this doesn't work, apparently since chan_sip doesn't use dnsmgr.

We figure that many other people must need to have Asterisk process updated
DNS info and that we must just be missing some configuration.  Is that the
case or is this a fundamental limitation of Asterisk in its current form?

Thanks in advance for the help,
-Joe

P.S. I'm subscribed to the list in digest form so a copy to this e-mail on
replies would be most appreciated.  Thanks!
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