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<p>Hello,</p>
<p>having use_dns_cache=no is not that bad if you have a local dns
cache application pointed by /etc/resolv.conf, provided that you
do not need srv based load balancing.<br>
</p>
<p>Not being the developer of dns resolving part in kamailio and the
dns cache, I investigated a bit and practically the /etc/hosts is
the pre-dns way of associating domains to ip addresses, without
ttl and other attributes specific to dns records. That seems the
reason the libc dns related functions do not use it implicitly,
thus also not reflected inside kamailio dns caching.</p>
<p>Now, you can add records to kamailio dns cache via rpc commands,
which can be done also from config using jsonrpc_exec() from
jsonrpcs module (e.g., using event_route[htable:mod-init] before
sip traffic is handled). The command should be liked:</p>
<p>kamctl rpc dns.add_a domain ttl ipaddr flags</p>
<p>The flags can be 1 to add it as a bad record (blacklisted domain)
or 2 to add it as permanent record (do not expire). You can use
dns.add_aaaa for ipv6.<br>
</p>
<p>Actually I am now thinking to add the possibility to add to dns
cache via modparam of ipops module, to make it easier overall.</p>
<p>Cheers,<br>
Daniel<br>
</p>
<div class="moz-cite-prefix">On 20.05.20 19:35, George
Diamantopoulos wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAPcKEYMmrLxoLvS1_hw_kKXFA7JGt5ohEk9_Pf5z5it94e0Mxg@mail.gmail.com">
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<div dir="ltr">
<div>Hello all,</div>
<div><br>
</div>
<div>Thank you for your enlightening answers. I ended up
creating DNS entries anyway, so it's all good now.
use_dns_cache=no sounded a little scary :-).<br>
</div>
<div><br>
</div>
<div>BR.</div>
<div>George<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, 19 May 2020 at
19:44, Daniel-Constantin Mierla <<a
href="mailto:miconda@gmail.com" moz-do-not-send="true">miconda@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">A quick follow up as I
found quite interesting that nowadays *BSDs allow<br>
specifying order of lookup in resolv.conf to include the
hosts file, but<br>
that doesn't seem to be in Linux:<br>
<br>
* <a href="https://man.openbsd.org/resolv.conf.5#lookup"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://man.openbsd.org/resolv.conf.5#lookup</a><br>
<br>
Cheers,<br>
Daniel<br>
<br>
<br>
On 19.05.20 17:48, Daniel-Constantin Mierla wrote:<br>
> Hello,<br>
><br>
> worth to clarify that Kamailio doesn't implement a dns
resolver from<br>
> scratch, it still uses the functions from libc. It only
does caching and<br>
> try to use cashing records first.<br>
><br>
> By default, the following dns functions are used
internally when the<br>
> cache doesn't have the record already -- they are set
in the dns_func<br>
> structure:<br>
><br>
> struct dns_func_t dns_func = {<br>
> res_init,<br>
> res_search,<br>
> gethostbyname,<br>
> #ifdef HAVE_GETHOSTBYNAME2<br>
> gethostbyname2<br>
> #else<br>
> NULL<br>
> #endif<br>
> };<br>
><br>
> So practically by leveraging res_init()/res_search() is
relying on<br>
> /etc/resolv.conf to do DNS queries, which is not using
the /etc/hosts<br>
> (iirc). For more see:<br>
><br>
> * <a href="https://linux.die.net/man/3/res_search"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://linux.die.net/man/3/res_search</a><br>
><br>
> Cheers,<br>
> Daniel<br>
><br>
> On 19.05.20 17:23, Alex Balashov wrote:<br>
>> You are correct that Kamailio does not use the libc
resolver /<br>
>> libresolv, but rather its own resolver, which
ignores /etc/hosts.<br>
>><br>
>> -- Alex<br>
>><br>
>> On 5/19/20 10:42 AM, George Diamantopoulos wrote:<br>
>>> Hello all,<br>
>>><br>
>>> I've come across this today when trying to
setup DMQ replication:<br>
>>><br>
>>> root@sbcpub0-stage-lhe0-cn1:/root# systemctl
restart kamailio<br>
>>> root@sbcpub0-stage-lhe0-cn1:/root# kamcmd
dmq.list_nodes<br>
>>> {<br>
>>> host: 172.30.154.189<br>
>>> port: 5090<br>
>>> resolved_ip: 172.30.154.189<br>
>>> status: active<br>
>>> last_notification: 0<br>
>>> local: 1<br>
>>> }<br>
>>> root@sbcpub0-stage-lhe0-cn1:/root# getent hosts<br>
>>> <a href="http://dmq-ng.services.domain.com"
rel="noreferrer" target="_blank" moz-do-not-send="true">dmq-ng.services.domain.com</a>
<<a href="http://dmq-ng.services.domain.com"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://dmq-ng.services.domain.com</a>><br>
>>> 172.30.154.189 <a
href="http://dmq-ng.services.domain.com" rel="noreferrer"
target="_blank" moz-do-not-send="true">dmq-ng.services.domain.com</a><br>
>>> <<a href="http://dmq-ng.services.domain.com"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://dmq-ng.services.domain.com</a>><br>
>>> 172.17.130.13 <a
href="http://dmq-ng.services.domain.com" rel="noreferrer"
target="_blank" moz-do-not-send="true">dmq-ng.services.domain.com</a><br>
>>> <<a href="http://dmq-ng.services.domain.com"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://dmq-ng.services.domain.com</a>><br>
>>><br>
>>> root@sbcpub0-stage-lhe0-cn1:/root# grep dmq-ng
/etc/kamailio/*<br>
>>>
/etc/kamailio/kamailio-module-params.cfg:modparam("dmq",<br>
>>> "notification_address", "sip:<a
href="http://dmq-ng.services.domain.com:5090"
rel="noreferrer" target="_blank" moz-do-not-send="true">dmq-ng.services.domain.com:5090</a><br>
>>> <<a
href="http://dmq-ng.services.domain.com:5090"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://dmq-ng.services.domain.com:5090</a>>")<br>
>>><br>
>>> In another case, where the resolving IPs for
the DMQ service hostname<br>
>>> were listed as A records in DNS, this worked as
expected.<br>
>>> In this case, the second host of the DMQ group
is not listed in<br>
>>> dmq.list_nodes, despite its being set in
/etc/hosts, as shown by the<br>
>>> getent command.<br>
>>><br>
>>> Doesn't kamailio use nss for hostname
resolution? Am I missing<br>
>>> something else? Thanks!<br>
>>><br>
>>> BR,<br>
>>> George<br>
>>><br>
>>><br>
>>> _______________________________________________<br>
>>> Kamailio (SER) - Users Mailing List<br>
>>> <a href="mailto:sr-users@lists.kamailio.org"
target="_blank" moz-do-not-send="true">sr-users@lists.kamailio.org</a><br>
>>> <a
href="https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users</a><br>
>>><br>
>> -- <br>
>> Alex Balashov | Principal | Evariste Systems LLC<br>
>><br>
>> Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free)<br>
>> Web: <a href="http://www.evaristesys.com/"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://www.evaristesys.com/</a>,
<a href="http://www.csrpswitch.com/" rel="noreferrer"
target="_blank" moz-do-not-send="true">http://www.csrpswitch.com/</a><br>
>><br>
>> _______________________________________________<br>
>> Kamailio (SER) - Users Mailing List<br>
>> <a href="mailto:sr-users@lists.kamailio.org"
target="_blank" moz-do-not-send="true">sr-users@lists.kamailio.org</a><br>
>> <a
href="https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users</a><br>
> -- <br>
> Daniel-Constantin Mierla -- <a
href="http://www.asipto.com" rel="noreferrer"
target="_blank" moz-do-not-send="true">www.asipto.com</a><br>
> <a href="http://www.twitter.com/miconda"
rel="noreferrer" target="_blank" moz-do-not-send="true">www.twitter.com/miconda</a>
-- <a href="http://www.linkedin.com/in/miconda"
rel="noreferrer" target="_blank" moz-do-not-send="true">www.linkedin.com/in/miconda</a><br>
> Funding: <a href="https://www.paypal.me/dcmierla"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://www.paypal.me/dcmierla</a><br>
><br>
-- <br>
Daniel-Constantin Mierla -- <a href="http://www.asipto.com"
rel="noreferrer" target="_blank" moz-do-not-send="true">www.asipto.com</a><br>
<a href="http://www.twitter.com/miconda" rel="noreferrer"
target="_blank" moz-do-not-send="true">www.twitter.com/miconda</a>
-- <a href="http://www.linkedin.com/in/miconda"
rel="noreferrer" target="_blank" moz-do-not-send="true">www.linkedin.com/in/miconda</a><br>
Funding: <a href="https://www.paypal.me/dcmierla"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://www.paypal.me/dcmierla</a><br>
<br>
<br>
_______________________________________________<br>
Kamailio (SER) - Users Mailing List<br>
<a href="mailto:sr-users@lists.kamailio.org" target="_blank"
moz-do-not-send="true">sr-users@lists.kamailio.org</a><br>
<a
href="https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users</a><br>
</blockquote>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
Kamailio (SER) - Users Mailing List
<a class="moz-txt-link-abbreviated" href="mailto:sr-users@lists.kamailio.org">sr-users@lists.kamailio.org</a>
<a class="moz-txt-link-freetext" href="https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users">https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users</a>
</pre>
</blockquote>
<pre class="moz-signature" cols="72">--
Daniel-Constantin Mierla -- <a class="moz-txt-link-abbreviated" href="http://www.asipto.com">www.asipto.com</a>
<a class="moz-txt-link-abbreviated" href="http://www.twitter.com/miconda">www.twitter.com/miconda</a> -- <a class="moz-txt-link-abbreviated" href="http://www.linkedin.com/in/miconda">www.linkedin.com/in/miconda</a>
Funding: <a class="moz-txt-link-freetext" href="https://www.paypal.me/dcmierla">https://www.paypal.me/dcmierla</a></pre>
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