Summary:ASTERISK-04965: DNS SRV lookups fail using BIND lightweight resolver
Reporter:Rick Alm (rickalm)Labels:
Date Opened:2005-09-01 14:07:47Date Closed:2011-06-07 14:02:43
Versions:Frequency of
Description:Using the following in sip.conf


causes the following error

Sep  1 13:56:33 WARNING[30580]: acl.c:226 ast_get_ip_or_srv: Unable to lookup ''

traced to a bug in srv.c where res_nsearch returns a 1 instead of a 0 on failed DNS lookups

patch included in comments


disclaimer on fax machine now

--- srv.c       2005-09-01 13:56:19.142079472 -0500
+++ srv.c.rea   2005-09-01 13:56:08.980624248 -0500
@@ -113,10 +113,11 @@
       if (chan)
               ret |= ast_autoservice_stop(chan);

-       if (ret <= 0) {
+       if (ret <= 1) {
               host[0] = '\0';
               *port = -1;
-               return ret;
+               ret=0;
       return ret;
Comments:By: Rick Alm (rickalm) 2005-09-01 14:20:22

uname -a

Linux server3.misdoctor.com 2.6.10-1.771_FC2smp #1 SMP Mon Mar 28 01:10:51 EST 2005 i686 athlon i386 GNU/Linux

By: Kevin P. Fleming (kpfleming) 2005-09-01 17:48:17

The only docs I can find say res_nsearch is supposed to return -1 in the case of a  failure... what version of the BIND resolver library is on your machine?

By: Brian West (bkw918) 2005-09-01 20:20:46

Do you have srv lookups on?


By: Rick Alm (rickalm) 2005-09-02 07:57:59

[root@server3 lib]# grep res_nsearch *
Binary file libnss1_dns-2.3.3.so matches
Binary file libnss_dns-2.3.3.so matches
Binary file libresolv-2.3.3.so matches

[root@server3 asterisk]# cat /proc/version
Linux version 2.6.10-1.771_FC2smp (bhcompile@porky.build.redhat.com) (gcc version 3.3.3 20040412 (Red Hat Linux 3.3.3-7)) #1 SMP Mon Mar 28 01:10:51 EST 2005

from sip.conf

srvlookup=yes                   ; Enable DNS SRV lookups on outbound calls

By: Brian West (bkw918) 2005-09-02 09:58:02

find me on #asterlink I wanna look at this.


By: Kevin P. Fleming (kpfleming) 2005-09-02 16:13:17

Unless you find documentation that says res_nsearch can return a positive value in a failure case, I'm very hesitant to change this code.

By: Rick Alm (rickalm) 2005-09-06 15:41:27

Still researching, recient version of srv.c uses ast_search_dns. Discovered that resololver is searching for


and then on failure trying

_sip._udp.switch-1.asterlink.com.misdoctor.com (misdoctor.com is my domain)

its matching with a CNAME (unexpected, doesnt do recursive and see that no SRV record is accociated) but since my DNS server has a "*" entry it resolves to my CNAME record. Thus returns a DNS result with NO valid data triggering the problems

Temporary workaround is to end all FQDN entries in sip.conf with a '.' preventing local domain lookups

When I have a valid patch will post it.

By: Mark Spencer (markster) 2005-09-13 11:05:39

The manual page for res_nsearch *clearly* states that -1 is returned on failure or the number of bytes of answer (which could be 0).  Clearly 1 is *not* a failure condition, and this is a bug in the resolver you are using, not in Asterisk.