DNS A records not being queried RRS feed

  • Question

  • I posted this under another thread, but perhaps this is a better topic.  We have followed the Planning and Deployment Guides, and encountered the following text specific to DNS entries required for client connectivity:

    Client DNS Queries

    During DNS lookup, SRV records are queried in the following order:

    1.          _sipinternaltls._tcp.domain - for internal TLS connections

    2.         _sipinternal._tcp.domain - for internal TCP connections (performed only if TCP is allowed)

    3.         _sip._tls.domain - for external TLS connections

    4.        _sip._tcp.domain - for external TCP connections

    If any query succeeds, the client uses the SRV record that is returned and does not continue querying for any other SRV records.

    After the SRV record is returned, a query is performed for the DNS A record for the host name that is returned by the SRV record. If no records are found during the DNS SRV query, the client performs an explicit lookup of sip.domain. If the explicit lookup does not produce results, the client performs a lookup for sipinternal.domain. If the client does not find sipinternal.domain, it performs a lookup for sipexternal.domain.


    Our problem is that our non-Microsoft DNS server DOES NOT SUPPORT SRV RECORDS.  Therefore we have created A records for our servers for "sip.domain" as above assuming that the client will explicitly query for this A record once the SRV record queries fail.  However, we are finding that these queries do not occur - a packet sniffer run after an ipconfig /flushdns shows the four SRV record queries in the order above, but then the client returns the connection failed error message, without making any of the three explicit A record queries mentioned above.  What's going on here, is this an error in the documentation, or an error in the behaviour in the client, and will this be fixed for GA?  This will cause serious problems for any organizations that do not or cannot implement SRV records.


    Thanks, Ben.

    Wednesday, July 25, 2007 8:10 PM


  • FYI, this issue is somewhat resolved in the RTM release of the Live Meeting console, and therefore I assume the Communicator client also.  The client still does not query A records for sipinternal.domain or sipexternal.domain, but does query for sip.domain after the four SRV record queries fail.

    Tuesday, July 31, 2007 7:02 PM