[SR-Users] [sr-dev] dns resolver issue (RFC3263)

Iñaki Baz Castillo ibc at aliax.net
Tue Nov 6 18:39:19 CET 2012

2012/11/6 Klaus Darilion <klaus.mailinglists at pernau.at>:
> Kamailio does the following lookups:
> 1. NAPTR cisco.com (no result)
> 2. SRV _sip._udp.cisco.com (NXDOMAIN)
> 3. A cisco.com -> Bingo -> use SIP over UDP to Cisco's web server :-(

Then really wrong...

After NAPTR query (with no result) it should look for SRV records for
TLS, TCP and then UDP (maybe also SCTP) in an order configured by
local policy (Kamailio DNS settings).

This is really clear in RFC 3263 section 4.1:

   If no NAPTR records are found, the client constructs SRV queries for
   those transport protocols it supports, and does a query for each.
   Queries are done using the service identifier "_sip" for SIP URIs and
   "_sips" for SIPS URIs.  A particular transport is supported if the
   query is successful.  The client MAY use any transport protocol it
   desires which is supported by the server.

   If no SRV records are found, the client SHOULD use TCP for a SIPS
   URI, and UDP for a SIP URI.  However, another transport protocol,
   such as TCP, MAY be used if the guidelines of SIP mandate it for this
   particular request.

Why is this not implemented?

Issue open at http://sip-router.org/tracker/index.php?do=details&task_id=253

Iñaki Baz Castillo
<ibc at aliax.net>

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