[SR-Users] Iterative DNS resolution by enum module ?

Måns Nilsson mansaxel at besserwisser.org
Wed Apr 22 13:54:07 CEST 2015

Subject: [SR-Users] Iterative DNS resolution by enum module ? Date: Wed, Apr 22, 2015 at 11:36:56AM +0200 Quoting jyaim (jyaime at gmail.com):
> Hello everyone,
> Do you know if the kamailio enum module is able to process
> 'recursives' dns requests in case of CNAME or NS response, until a
> NAPTR answer is returned ?

For NS, any recursive resolver does that. 

For CNAME, beware. CNAME is dominant; on a node in the DNS tree where
there is a CNAME, no other record can be present. Of course, it is
entirely possible to have:

fancy.domain.tel. CNAME standard.domain.tel.

and then put for instance: 

standard.domain.tel. NAPTR 10 0 "S" "SIP+D2U" "" _sip._udp.telco.tel

What is explicitly forbidden is this: 

fancy.domain.tel. IN SOA strowger.axe.tel. root.tel. 17 .... 
fancy.domain.tel. IN CNAME lame.web.host.
www.fancy.domain.tel. IN CNAME lame.web.host.

Look here for something that does work: 

$ dig fancy.sub.besserwisser.org NAPTR

; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> fancy.sub.besserwisser.org NAPTR
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2322
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 0

;fancy.sub.besserwisser.org.    IN      NAPTR

fancy.sub.besserwisser.org. 27  IN      CNAME   simple.sub.besserwisser.org.
simple.sub.besserwisser.org. 27 IN      NAPTR   10 0 "S" "SIP+D2U" "" _sip._udp.boring.sub.besserwisser.org.

sub.besserwisser.org.   27      IN      NS      primary.se.

If you query for NAPTR but the resolver encounters a CNAME, it will
attempt to follow the redirection and then presents whatever answer or
lack thereof back. There is no need to do any resolver functionality in
the application layer; the answers are there. Perhaps the code handling
the response from the system resolver needs to be updated, but that is
another thing.

Måns Nilsson     primary/secondary/besserwisser/machina
MN-1334-RIPE                             +46 705 989668
Look!  A ladder!  Maybe it leads to heaven, or a sandwich!
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