[SR-Users] Kamailio not using system resolver for hostname resolution (DMQ)?

[George Diamantopoulos]

Hello all,

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.
George

On Tue, 19 May 2020 at 19:44, Daniel-Constantin Mierla <miconda at gmail.com>
wrote:

> A quick follow up as I found quite interesting that nowadays *BSDs allow
> specifying order of lookup in resolv.conf to include the hosts file, but
> that doesn't seem to be in Linux:
>
>   * https://man.openbsd.org/resolv.conf.5#lookup
>
> Cheers,
> Daniel
>
>
> On 19.05.20 17:48, Daniel-Constantin Mierla wrote:
> > Hello,
> >
> > worth to clarify that Kamailio doesn't implement a dns resolver from
> > scratch, it still uses the functions from libc. It only does caching and
> > try to use cashing records first.
> >
> > By default, the following dns functions are used internally when the
> > cache doesn't have the record already -- they are set in the dns_func
> > structure:
> >
> > struct dns_func_t dns_func = {
> >     res_init,
> >     res_search,
> >     gethostbyname,
> > #ifdef HAVE_GETHOSTBYNAME2
> >     gethostbyname2
> > #else
> >     NULL
> > #endif
> > };
> >
> > So practically by leveraging res_init()/res_search() is relying on
> > /etc/resolv.conf to do DNS queries, which is not using the /etc/hosts
> > (iirc). For more see:
> >
> >   * https://linux.die.net/man/3/res_search
> >
> > Cheers,
> > Daniel
> >
> > On 19.05.20 17:23, Alex Balashov wrote:
> >> You are correct that Kamailio does not use the libc resolver /
> >> libresolv, but rather its own resolver, which ignores /etc/hosts.
> >>
> >> -- Alex
> >>
> >> On 5/19/20 10:42 AM, George Diamantopoulos wrote:
> >>> Hello all,
> >>>
> >>> I've come across this today when trying to setup DMQ replication:
> >>>
> >>> root at sbcpub0-stage-lhe0-cn1:/root# systemctl restart kamailio
> >>> root at sbcpub0-stage-lhe0-cn1:/root# kamcmd dmq.list_nodes
> >>> {
> >>>          host: 172.30.154.189
> >>>          port: 5090
> >>>          resolved_ip: 172.30.154.189
> >>>          status: active
> >>>          last_notification: 0
> >>>          local: 1
> >>> }
> >>> root at sbcpub0-stage-lhe0-cn1:/root# getent hosts
> >>> dmq-ng.services.domain.com <http://dmq-ng.services.domain.com>
> >>> 172.30.154.189 dmq-ng.services.domain.com
> >>> <http://dmq-ng.services.domain.com>
> >>> 172.17.130.13 dmq-ng.services.domain.com
> >>> <http://dmq-ng.services.domain.com>
> >>>
> >>> root at sbcpub0-stage-lhe0-cn1:/root# grep dmq-ng /etc/kamailio/*
> >>> /etc/kamailio/kamailio-module-params.cfg:modparam("dmq",
> >>> "notification_address", "sip:dmq-ng.services.domain.com:5090
> >>> <http://dmq-ng.services.domain.com:5090>")
> >>>
> >>> In another case, where the resolving IPs for the DMQ service hostname
> >>> were listed as A records in DNS, this worked as expected.
> >>> In this case, the second host of the DMQ group is not listed in
> >>> dmq.list_nodes, despite its being set in /etc/hosts, as shown by the
> >>> getent command.
> >>>
> >>> Doesn't kamailio use nss for hostname resolution? Am I missing
> >>> something else? Thanks!
> >>>
> >>> BR,
> >>> George
> >>>
> >>>
> >>> _______________________________________________
> >>> Kamailio (SER) - Users Mailing List
> >>> sr-users at lists.kamailio.org
> >>> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users
> >>>
> >> --
> >> Alex Balashov | Principal | Evariste Systems LLC
> >>
> >> Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free)
> >> Web: http://www.evaristesys.com/, http://www.csrpswitch.com/
> >>
> >> _______________________________________________
> >> Kamailio (SER) - Users Mailing List
> >> sr-users at lists.kamailio.org
> >> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users
> > --
> > Daniel-Constantin Mierla -- www.asipto.com
> > www.twitter.com/miconda -- www.linkedin.com/in/miconda
> > Funding: https://www.paypal.me/dcmierla
> >
> --
> Daniel-Constantin Mierla -- www.asipto.com
> www.twitter.com/miconda -- www.linkedin.com/in/miconda
> Funding: https://www.paypal.me/dcmierla
>
>
> _______________________________________________
> Kamailio (SER) - Users Mailing List
> sr-users at lists.kamailio.org
> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users
>
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