SRV record target must not be CNAME
First, thanks for the RTC quickstart guide. However, it looks like
the instructions in  to set up the DNS for a RTC communication
server are incorrect with regard to the use of CNAMEs.
Following the instructions, my setup did only connect to some servers
(observed with XMPP s2s connections). After switching from CNAMEs to
A respectively AAAA records, the problem disappeared. It seems 
that using a CNAME as target in SRV records is not valid and causes
Thanks and best regards,
'… the target in SRV records must point to hostname with an address
record (A or AAAA record). Pointing to a hostname with a CNAME
record is not a valid configuration.'