This article describes the DNS lookup configuration required to allow endpoints and clients to access Breeze Connect services.
What are SIP DNS SRV records?
Let us say your name is Bob and you work for a company called Acme Corp. Your company has recently signed up for a corporate VoIP phone system and you’re given a SIP address, Bob@acme.com. In an ideal world, your friends and colleagues who are also familiar with VoIP know that they can dial Bob@acme.com to reach you wherever you have a device registered.
When someone calls you at Bob@acme.com, the SRV record tells their SIP phone to do so by connecting to the domain belonging to your VoIP phone system (SIP) provider. This allows the SIP provider to ensure greater stability.
The SRV RR allows Breeze Connect to use several servers for a single domain, to move services from host to host with little fuss, and to designate some hosts as primary servers for a service and others as backups.
If for some reason the ‘host’ with the highest priority cannot be reached, the SIP phone or proxy trying to reach the user within the domain will attempt to reach the next host defined within the SRV record.
Controlling DNS lookup on different endpoints
In the “General” tab next to the Registrar and Outbound Proxy fields there is the option “Auto-Discovery”. When this option is disabled, the port must be manually specified. In this configuration 3CX will not attempt to look for NAPTR or SRV entries, it will only check for A or AAAA records.
When “Auto-Discovery” is enabled, the port is determined automatically from the SRV entry. When no SRV entry is found, the port is assumed to be 5060. Enable “Auto-Discovery” to configure your BreezeConnect trunk for failover in the event that the main site is unavailable.
In the “FXS Port” tab look for DNS Mode. Enable “NAPRT/SRV” to configure your BreezeConnect trunk for failover in the event that the Main site is unavailable.
In the “Voice” tab under “Line1/2” look for “Use DNS SRV”. Enable “Use DNS SRV” to configure your BreezeConnect trunk for failover in the event that the main site is unavailable.
In the “Account” tab under “SIP Server” look for “Transport”. Enable “DNS NAPTR” to configure your BreezeConnect trunk for failover in the event that the main site is unavailable.
If a port is set to 0 and the transport type is set to DNS-NAPTR, NAPTR and SRV queries
will be tried before falling back to A query. If no port is found through the DNS query,
5060 will be used. If an explicit port (except 0) is specified and the transport type is set
to DNS-NAPTR, the only lookup will be an A query.