[sr-dev] [tracker] Task opened: If no NAPTR then SRV must be queried for more than UDP

[sip-router]

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A new Flyspray task has been opened.  Details are below. 

User who did this - Iñaki Baz Castillo (ibc) 

Attached to Project - sip-router
Summary - If no NAPTR then SRV must be queried for more than UDP
Task Type - Bug Report
Category - dns / dns cache
Status - New
Assigned To - 
Operating System - All
Severity - Medium
Priority - Normal
Reported Version - Development
Due in Version - Undecided
Due Date - Undecided
Details - As discussed in the maillist, 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 :-(

Step 2 is 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.


More information can be found at the following URL:
http://sip-router.org/tracker/index.php?do=details&task_id=253

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