What is an SRV record?
An SRV (Service) record is a DNS entry that specifies the hostname and port number for a particular service running on a domain. Unlike A or CNAME records — which simply resolve a name to an address — SRV records carry additional information about how to reach a specific service: which server handles it, which port it runs on, and how to prioritise and load-balance between multiple servers.
SRV records are commonly used for services like SIP (VoIP telephony), XMPP (instant messaging), Microsoft Teams, and various other protocols that need to advertise their endpoints via DNS. They follow a standardised naming format: _service._protocol.domain — for example, _sip._tcp.example.com.
How SRV record naming works
Every SRV record name has three parts. The first part is the service name, prefixed with an underscore (e.g. _sip for the SIP telephony protocol). The second part is the transport protocol, also prefixed with an underscore (e.g. _tcp or _udp). The third part is the domain name itself. Together they form a fully qualified name like _xmpp-client._tcp.example.com. The underscore prefix ensures SRV names never conflict with regular hostnames.
Understanding the components of an SRV record
An SRV record contains four data fields in addition to the standard DNS name and TTL. Priority works the same way as in MX records — the server with the lowest priority number is contacted first. If it is unavailable, the next lowest priority is tried. Weight is used to distribute load between servers that share the same priority. A server with a higher weight receives a proportionally larger share of connections. Port specifies which TCP or UDP port the service is listening on. Target is the hostname of the server providing the service — it must point to an A or AAAA record and cannot be a CNAME.
Why use SRV records?
SRV records let applications discover service endpoints automatically through DNS, without needing hard-coded IP addresses or port numbers. A client that supports SRV lookups can find the correct server and port for a service by querying DNS, even as infrastructure changes over time. This is particularly useful in enterprise environments where multiple servers run the same service at different ports or locations, and where load balancing and failover need to be managed at the DNS level.
How to use the SRV lookup tool
Enter a full SRV record name — such as _sip._tcp.example.com — in the search field and click Lookup. If you enter a bare domain name, the tool will query for any SRV records associated with it. Results are returned sorted by priority and weight, showing all the information needed to understand how a service's traffic is routed.
Frequently Asked Questions
What is the difference between a CNAME record and an SRV record?
A CNAME maps one hostname to another — it is purely about name aliasing and does not carry any service-specific information. An SRV record defines where a specific service lives, including the exact hostname and port it runs on, plus priority and weight values for load balancing. SRV records are used by applications that need to discover service endpoints automatically through DNS.
What is the difference between an A record and an SRV record?
An A record maps a hostname to an IPv4 address. An SRV record points to a hostname (which itself must have an A or AAAA record) and additionally specifies the port and protocol details for a particular service. Where an A record tells you where a server is, an SRV record tells you where a specific service on that server is and how to prioritise connections to it.
What happens when two SRV records have the same priority?
When multiple SRV records share the same priority level, the weight field determines how traffic is distributed between them. A server with a higher weight receives a proportionally greater share of requests. If two servers have both the same priority and the same weight, connections are distributed equally between them in a round-robin manner.
Can an SRV record point to a CNAME?
No. The DNS specification requires that the target of an SRV record must be a hostname with its own A or AAAA record — it cannot be an alias created via a CNAME. Configuring an SRV target that points to a CNAME may work in practice with some resolvers, but it is not compliant with the standard and can cause unpredictable behaviour across different DNS implementations.
Which services commonly use SRV records?
SRV records are used by many widely deployed services and protocols. SIP (Session Initiation Protocol) uses them for VoIP call routing. XMPP uses them for instant messaging client and server connections. Microsoft services including Teams, Lync, and Skype for Business rely on SRV records for service discovery. CalDAV and CardDAV (calendar and contact syncing), as well as some game servers and distributed databases, also make use of SRV records for endpoint discovery.