HTTPS and SVCB records are DNS record types that help browsers and applications find the best way to connect to a service. They publish service binding information in DNS, which means they can tell a client where a service is available, which protocols it supports, and what connection options it should use.
They can provide extra information before the connection starts, such as which protocol to use, which server to contact, or whether the service supports modern features like HTTP/2 and HTTP/3.
The HTTPS record is used for websites and web services. It gives extra information about how a domain should be reached over HTTPS. For example, an HTTPS record can tell a browser that a website supports HTTP/3.
Example:
| Host | Type | Priority | Points to: | Parameters | TTL |
| www | HTTPS | 4334 | example.com | alpn=h3 no-default-alpn | 3600 |
SVCB stands for Service Binding. It is a more general DNS record that helps clients find the correct service endpoint and learn how to connect to it. It can include details such as the target hostname, supported protocols, custom ports, or other connection parameters.
Example:
| Host | Type | Priority | Points to: | Parameters | TTL |
| something | SVCB | 2 | cloudns.com | alpn=h2 | 3600 |
HTTPS and SVCB records have a similar structure, but they are used for different purposes. The HTTPS record is mainly used for HTTP and HTTPS services, such as websites and web applications. The SVCB record is more general and can be used for other services that support service binding.
For HTTPS records, the HTTP/HTTPS service is already implied, so the record is usually added directly to the hostname. SVCB records are used when a service needs to define its own service binding information.
In simple words, use HTTPS records for websites and use SVCB records only when the service or protocol requires them.
When a browser or application wants to connect to a domain, it can check for an HTTPS or SVCB record. If such a record exists, the client can use the information inside it to choose the best connection method.
For example, the record may show that HTTP/2 or HTTP/3 is supported, that the service is available on another hostname, that a different port should be used, or that IPv4 and IPv6 address hints are available. This helps the client make a better decision before it starts the connection.
Older clients that do not support these records can simply ignore them and continue using the normal A or AAAA records.
The priority is the number after the record type. Lower values are preferred first. For example, a record with priority 2 is preferred before a record with priority 4334.
A priority of 0 has a special meaning. It is used for alias mode, where the record points the service to another hostname. A priority greater than 0, such as 2 or 4334, is used when the record describes a service endpoint and its parameters.
Some common parameters used with HTTPS and SVCB records are alpn, no-default-alpn, port, ipv4hint, ipv6hint, mandatory, and ech.
The alpn parameter shows which protocols are supported, for example, h2 for HTTP/2 or h3 for HTTP/3. The no-default-alpn parameter means that the client should not assume or use a default protocol that is not listed in alpn. The port parameter shows a custom port for the service. The ipv4hint and ipv6hint parameters provide IP address hints. The mandatory parameter lists service parameters that the client must understand to use the record. The ech parameter is used for Encrypted ClientHello support.
No. A and AAAA records are still used to point a domain to an IP address. HTTPS and SVCB records only provide extra connection information.
No. It is optional. Use it only when you need it or when your provider recommends it.
It will ignore the record and continue with normal DNS resolution.