SVCB record
An SVCB (service binding) record describes how to connect to a service: which host, port, protocols and keys to use. It's the general form of the HTTPS record, used by protocols other than the web, most often by DNS resolvers announcing DNS-over-HTTPS and DNS-over-TLS.
| Record type | SVCB |
|---|---|
| Type number | 64 |
| Used for | Services |
| How common | Specialist |
| Defined in | RFC 9460, RFC 9461 |
Format
<_service.name> <ttl> IN SVCB <priority> <target> [key=value ...]
| Field | What it means | Accepted values |
|---|---|---|
| Priority | 0 is alias mode; 1 or more is service mode, lower preferred. | 0 to 65535. |
| Target | The host offering the service; . means this name. | A host name or .. |
| Parameters | alpn, port, ipv4hint, ipv6hint, ech, mandatory, dohpath, and others defined per protocol. | key=value pairs separated by spaces. |
Check an SVCB record
Type or paste a record in zone-file form (name, TTL, type, value) or just its value. Each part is explained as you type.
A valid SVCB record.
| Part | What it means |
|---|---|
| Name_dns.resolver.example. | A full name: the final dot means nothing is added to it. |
| TTL300 | Resolvers may keep this answer for 5 minutes before asking again. Changes can take that long to reach everyone. |
| ClassIN | Internet. Every record you'll write uses IN. |
| TypeSVCB | Service binding: endpoints and settings. |
| Priority1 | 1: service mode. Lower numbers are preferred. |
| Targetdoh.example.net. | The host name this record points to. |
| alpnalpn=h2 | Protocols the server speaks: h3 is HTTP/3 (QUIC), h2 is HTTP/2, http/1.1. Lets browsers start with HTTP/3 straight away. |
| dohpathdohpath=/dns-query{?dns} | The DNS-over-HTTPS path template, for DNS resolvers. |
Examples
A resolver offering DNS-over-HTTPS
_dns.resolver.example. 300 IN SVCB 1 doh.example.net. alpn=h2 dohpath=/dns-query{?dns}Clients that discover this resolver can switch to encrypted DNS over HTTPS.
DNS-over-TLS on port 853
_dns.resolver.example. 300 IN SVCB 2 dot.example.net. alpn=dot port=853
A second option with a higher priority number, tried after the first.
Look up SVCB records
TTL
300 to 3600. How TTL works
Common mistakes
- Using SVCB for a website. Browsers look up HTTPS records; use HTTPS.
- Leaving out a parameter the protocol requires, such as dohpath for DNS-over-HTTPS.
At your DNS host
- Cloudflare, Route 53 and Google Cloud DNS support SVCB. Many registrar panels don't.
Questions
Where are SVCB records used today?
Mainly for Discovery of Designated Resolvers: a DNS resolver publishes SVCB records at _dns.resolver.arpa and its own name so devices can upgrade to encrypted DNS.
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