Quick definition: An SRV record is a DNS resource record that specifies the location, including the hostname and port number, of servers for specific services like VoIP or instant messaging.
Explanation
An SRV Record, or Service Record, is a specialized type of Domain Name System (DNS) resource record used to identify the location of specific services on a network. Unlike standard A records that only map a domain to an IP address, an SRV record specifies both the hostname and the exact port number for services like VoIP, instant messaging, or directory services. It operates using a structured format that includes the service name, protocol, priority, and weight. Priority and weight values allow administrators to implement failover and load balancing by directing traffic to preferred or more capable servers.
A common misconception is that SRV records can be used for any application; however, they only function if the specific software is programmed to query them, which is why most web browsers ignore them for standard HTTP traffic. Additionally, some mistakenly believe SRV records can point directly to an IP address or a CNAME, but they must point to a canonical hostname with an existing A or AAAA record to resolve correctly.
Why it matters
- – Helps your devices automatically find and connect to specific online services like video calling, instant messaging, and office tools without manual setup
- – Improves the reliability of your favorite apps by directing traffic to the best available server, ensuring smoother performance and less lag
- – Enhances your connection stability by allowing services to automatically switch to a backup server if the primary one experiences issues
How to check or fix
- – Verify the record follows the standard format of _service._protocol.domain to ensure it is correctly identified by client applications
- – Confirm the target hostname resolves to a valid A or AAAA record, as SRV records cannot point directly to IP addresses or CNAME aliases
- – Check that the port number is correctly specified and matches the configuration of the service running on the destination server
- – Validate the priority and weight settings to ensure traffic is correctly directed or load-balanced across multiple available servers
- – Use a command-line or web-based lookup tool to test if the record is visible to the public internet and reflects the intended values
- – Review the Time to Live (TTL) settings to ensure updates propagate quickly during testing or maintenance windows
Related terms
DNS, IP Address, Port Number, SIP, VoIP, XMPP
FAQ
Q: What is a DNS SRV record?
A: An SRV record is a type of DNS record that specifies the hostname and port number for specific services, such as VoIP or instant messaging. It allows client applications to discover where a service is located on a domain.
Q: How do priority and weight work in an SRV record?
A: Priority determines which server is contacted first, with lower numbers receiving higher preference. Weight is used to load balance traffic among multiple servers that have the same priority level.
Q: Can an SRV record point to a CNAME?
A: No, according to DNS standards, the target of an SRV record must point directly to an A or AAAA record. Pointing an SRV record to a CNAME record is generally not supported and can cause resolution issues.