Twillio and SRV

Created: 5/2015.  Last Updated: 1/2018


Twilio does not support RFC 3263, Locating SIP Servers. This is a standard way of locating SIP servers via SRV record lookup. Twilio, however, only attempts to resolve domains via A records, which is incompatible with OnSIP's distributed nature.

You can use a dig command to look up the SRV record for your SIP domain:

> dig SRV

;; ANSWER SECTION: 86400 IN SRV 0 0 5060

---, in turn, is resolved via GeoDNS to provide a reliable, distributed service entry point. To interoperate between Twilio and OnSIP, Twilio would need to add support for this standard. I'm sorry for the inconvenience.


Note: There does appear to be a work-around.  If you migrate your A-record domain to OnSIP, that does appear to work.  Since your domain has an A-record, Twilio will then do an SRV record lookup.  This is still backwards. They should attempt an SRV record lookup irrespective of whether or not an A-record exists.  

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