asterisk users - Nov 2005 - DNS Server Failure wreaks havoc

I don't think this is a new issue--I've seen it talked about on the list
before.  I don't know if I've ever seen anyone post a fix.

My DNS server went out last night in a horrendous storm when an upstream 
link went down.  The madness is that the behavior of the whole server, 
including the part that's handling my POTS lines, gets wigged out on a 
DNS failure, making the whole system unusable.  I have two questions; 
being able to solve either would be wonderful:

* Is it true that if I hand-resolve the server names in all the config 
files, and then use those instead of the hostnames, this problem won't 
occur?  That's not exactly optimal, of course, since it defeats the 
whole purpose of dynamic name binding.  But it's hard to explain to my 
SOHO customers, who don't really need any IP-based functionality 
(although I give all of them some complimentary minutes on nufone) why 
their phones go down when the Internet is down.

* Is it true that there's no way to get applications in Linux, generally 
speaking, to try more than a single server when doing a name resolve? 
Only the first server listed in /etc/resolv.conf (on my systems, anyway) 
seems to ever get consulted.

I think both of these situations are pretty serious failings, if in fact 
they're failings in the systems and not this bedeviled cranium.

Thanks.

B.

Brian Capouch wrote:
> I don't think this is a new issue--I've seen it talked about on the
list
> before.  I don't know if I've ever seen anyone post a fix.
> 
> My DNS server went out last night in a horrendous storm when an upstream 
> link went down.  The madness is that the behavior of the whole server, 
> including the part that's handling my POTS lines, gets wigged out on a 
> DNS failure, making the whole system unusable.  I have two questions; 
> being able to solve either would be wonderful:
Asterisk is horrible at handleing DNS failures.  Don't use DNS with 
Asterisk.

Brian Capouch wrote:
> I don't think this is a new issue--I've seen it talked about on the
list
> before.  I don't know if I've ever seen anyone post a fix.
> 
> My DNS server went out last night in a horrendous storm when an upstream
> link went down.  The madness is that the behavior of the whole server,
> including the part that's handling my POTS lines, gets wigged out on a
> DNS failure, making the whole system unusable.  I have two questions;
> being able to solve either would be wonderful:
Why don't you cache the DNS locally.  That way if the remote DNS goes down
you'll only lose updates.

-- 
Cheers,

Matt Riddell
_______________________________________________

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> I don't think this is a new issue--I've seen it talked about on the
list
> before.  I don't know if I've ever seen anyone post a fix.
> 
> My DNS server went out last night in a horrendous storm when an upstream 
> link went down.  The madness is that the behavior of the whole server, 
> including the part that's handling my POTS lines, gets wigged out on a 
> DNS failure, making the whole system unusable.  I have two questions; 
> being able to solve either would be wonderful:
> 
> * Is it true that if I hand-resolve the server names in all the config 
> files, and then use those instead of the hostnames, this problem won't 
> occur?  That's not exactly optimal, of course, since it defeats the 
> whole purpose of dynamic name binding.  But it's hard to explain to my 
> SOHO customers, who don't really need any IP-based functionality 
> (although I give all of them some complimentary minutes on nufone) why 
> their phones go down when the Internet is down.
Asterisk's use of dns is less then optimal. It expects a response,
and if that response contains multiple entries, all entries past the
first are ignored. If no response, you already know what happens.
Use numeric addresses, etc/hosts, or a dns cache on asterisk. 
 
> * Is it true that there's no way to get applications in Linux,
generally
> speaking, to try more than a single server when doing a name resolve? 
> Only the first server listed in /etc/resolv.conf (on my systems, anyway) 
> seems to ever get consulted.
That's true in most systems. If there are multiple entries, the first
one will be attempted, and if no response, the second (etc) will be
attempted.  If the first responds with _anything_ (even an unknown host),
that is considered a response and the dns client will not attempt the
second entry in resolv.conf.
> I think both of these situations are pretty serious failings, if in fact 
> they're failings in the systems and not this bedeviled cranium.

Using IPs only and no domains didn't do the trick for me, but then I  
may have missed one or two without realising. I did find that putting  
a DNS server in the asterisk box works perfectly for asterisk, but  
the grandstream budgetone 101 phones i had relied on a dns (even if i  
replaced the ntp server with an IP) and would not work without them.  
the symptom would be the call comes in (over ISDN), rings , but the  
phones don't pickup. This was not an issue for SPA-841s or SNOM 190s,  
both of which are perfectly happy with just IPs.

Funny things was that they weren't happy using the asterisk box's dns  
either - even though i could dig @192.168.1.254 domain.com from my  
laptop without problems.

I installed a caching dns server on the * box itself 'cause when the 
external dns stopped resolving guess where my emailed voicemails went? 
Ya, I don't know either.  :P  They weren't in the mailq but showed up 
just a little while later when the names began resolving again :)

Brian Capouch wrote:
> I don't think this is a new issue--I've seen it talked about on the
list
> before.  I don't know if I've ever seen anyone post a fix.
> 
> My DNS server went out last night in a horrendous storm when an upstream 
> link went down.  The madness is that the behavior of the whole server, 
> including the part that's handling my POTS lines, gets wigged out on a 
> DNS failure, making the whole system unusable.  I have two questions; 
> being able to solve either would be wonderful:
> 
> * Is it true that if I hand-resolve the server names in all the config 
> files, and then use those instead of the hostnames, this problem won't 
> occur?  That's not exactly optimal, of course, since it defeats the 
> whole purpose of dynamic name binding.  But it's hard to explain to my 
> SOHO customers, who don't really need any IP-based functionality 
> (although I give all of them some complimentary minutes on nufone) why 
> their phones go down when the Internet is down.
> 
> * Is it true that there's no way to get applications in Linux,
generally
> speaking, to try more than a single server when doing a name resolve? 
> Only the first server listed in /etc/resolv.conf (on my systems, anyway) 
> seems to ever get consulted.
> 
> I think both of these situations are pretty serious failings, if in fact 
> they're failings in the systems and not this bedeviled cranium.
> 
> Thanks.
> 
> B.
> 
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