This SIP SRV checker shows exactly what a SIP phone, trunk provider or federated server sees when it looks up your SIP domain in DNS. It follows the RFC 3263 lookup order: NAPTR records to pick a transport, SRV records to find host and port, then the address records of each target. Anything that would stop a client from finding your server is flagged with a fix.
Short answer: Enter the SIP domain (the part after the @ in SIP addresses). The checker lists NAPTR records, then the _sip._udp, _sip._tcp and _sips._tcp SRV records with priority, weight, port and target, and confirms every target has an A or AAAA record and is not a CNAME. Missing SRV records, CNAME targets and targets that do not resolve are the three problems it catches most often.
Table of Contents
What each result means
- NAPTR: optional. When present, clients use the lowest order value first; SIPS+D2T means TLS over TCP, SIP+D2T plain TCP and SIP+D2U UDP.
- SRV records: one per transport you offer. Lower priority numbers are tried first; weight splits traffic between records of equal priority.
- Target check: every target must resolve to an address directly. A CNAME target breaks some phones and PBXs even if a browser-style resolver follows it.
- Target “.”: a deliberate way to say a transport is not offered.
Typical fixes
Publish all three SRV records if your server supports UDP, TCP and TLS, point them at a hostname with its own A record, and keep TTLs between 300 and 3600 seconds so failover changes take effect quickly. The SIP SRV records guide has copy-ready zone file lines, and the SIP ports firewall guide covers opening 5060 and 5061 on the server side.
What it does not test
SIP over UDP cannot be probed reliably from outside because a closed port and a silent server look the same. Confirm reachability with a real registration from a softphone on a mobile network, or capture the traffic with sngrep on the PBX.
SIP SRV checker at a glance
Official documentation: RFC 3263: locating SIP servers, RFC 2782: DNS SRV.
Related: SIP SRV records guide · SIP ports firewall rules · DNS lookup.
Frequently asked questions
Do I need NAPTR records for SIP?
No. NAPTR records are optional and only express a transport preference. Without them, clients query the SRV records directly, usually starting with UDP.
Why is my SRV record flagged as a CNAME?
The SRV target hostname is itself a CNAME. RFC 2782 requires the target to have A or AAAA records, so point the SRV record at the final hostname instead.
Which SIP domain should I enter?
Enter the domain used in SIP addresses, for example example.com for user@example.com, not the hostname of the PBX itself.