[asterisk-users] DNS A queries for channel

[samuel]

It not only happens on INVITE or BYE but also happens when a 18x is received
(180 Ringing or 183 Session Progess at least) so it's not directly related
where the Dial command is executed in the dialplan, isn't it? It looks more
as a SIP channel internal stuff...

It looks like there is some gethostbyname (or similar) call whenever a SIP
message (request or response) is received that triggers the DNS query.

Shall I try to post in dev list?

Best regards,
Samuel.


2008/11/7 John Todd <jtodd at digium.com>

>
> 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
>
>
>
>
>
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