[asterisk-users] DNS A queries for channel

[John Todd]

On Nov 7, 2008, at 8:29 AM, samuel wrote:

> Hi folks,
>
> I've been using * for quite a few years and everyday it surprises me  
> more.
>
> I was recently analysing some captures with ethereal/wireshark and  
> found out that * was doing DNS A queries for domain names like  
> channel.mydomain.com where channel is the typical string of the  
> dstchannel or channel field in the CDR entries.
>
> Obviously those queries returned with negative answer because it  
> does not exists such domainname. My question is why is * asking the  
> DNS for the A entry of the channel? It looks like it does the DNS  
> query upon receiving a SIP message but none SIP header contains the  
> channel string in the SIP headers so it must be something internal,  
> maybe some end-point check?
> Considering how delicate is * to DNS failures I would like to know  
> whether this behaviour can be disabled in the config files because  
> it makes * block easier and charges the DNS server of senseless  
> queries.
>
> I don't know about * internals so it 's far beyond my knowledge  
> following the reception and treatment of SIP message throughout the  
> sip_channel.c code so I would really appreciate any hint about this  
> issue.
>
> The capture was done on a 1.4.18 version but I've checked same  
> behaviour (ngrep port 53) on other 1.4 and 1.2 installations. Does  
> anyone knows if this has changed in 1.6?
>
> Any help would be really appreciated.
>
> Thanks,
> Samuel.
>


That's an interesting discovery, but I suspect it has something to do  
with a Dial command on a SIP channel.  Do you have any idea where in  
your dialplan these events are occurring?

JT

---
John Todd
jtodd at digium.com        +1-256-428-6083
Asterisk Open Source Community Director