DNS SVCB (Service Binding) records provide a general framework for service discovery and connection optimization in DNS. These records enable applications to discover alternative service endpoints, supported protocols, and connection parameters, improving performance and reliability for various network services.
SVCB records, defined in RFC 9460, provide a flexible mechanism for publishing service information in DNS. These records include priority and weight values for service selection, along with extensible service parameters that can specify connection details such as supported protocols, port numbers, and endpoint alternatives.
SVCB records serve as the foundation for protocol-specific service binding records like HTTPS records. They provide a general framework that can be adapted for various services beyond just web traffic, enabling DNS-based service discovery for any network protocol.
Applications that support SVCB records query DNS for these records when connecting to a service. The records provide information about alternative endpoints, supported protocols, and connection parameters that enable clients to make optimal connection decisions based on their capabilities and requirements.
SVCB records can indicate protocol support (such as HTTP/2, HTTP/3, or QUIC), specify alternative port numbers, provide endpoint IP hints for faster connection establishment, or define service-specific parameters that affect client behavior.
The flexible parameter system in SVCB records allows for future extensibility as new protocols and connection optimization techniques are developed. This makes SVCB records a forward-looking solution for evolving network service requirements while maintaining backward compatibility.
Here's what an SVCB record looks like for the domain example.com:
