[asterisk-users] No retry after DNS failure

[James Harper]

> 
> Today I had a brief power outage which caused the Asterisk server and
> DSL modem to reboot. The Asterisk server came up before the internet
> connection was working, so it failed when try to look up some of the
> hosts for my outbound voip providers in sip.conf.
> 
> Asterisk never recovered from that, i.e. it never retried so those
> providers were unavailable. The only provider that was still available
> was one that I had entered the IP address for, rather than the host
name.
> 

<snip>

Are you sure that it was Asterisk? Did you try an nslookup after the
network came up while Asterisk wasn't working? How long did you leave it
before taking matters into your own hands?

DNS will do negative caching as well as positive. If sip.sometel.com
failed to resolve (because it doesn't exist or because your network
wasn't up), your caching dns server or resolver or both may remember
this as a 'negative cache' entry, so that it remembers that it doesn't
exist.

If your asterisk server is responsible for the network connection, then
the ifup/pon script should take care of flushing the dns cache for you
for exactly this reason.

If you have another server or router that is responsible for the
connection then the server running asterisk will have no idea that its
negative cache is no longer valid.

hth

James