# 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. |

## 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.

## TTL

300 to 3600.

## Common mistakes

- Using SVCB for a website. Browsers look up HTTPS records; use [HTTPS](https://lemon.domains/dns-records/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.

## Related

- [HTTPS record](https://lemon.domains/dns-records/https.md)
- [SRV record](https://lemon.domains/dns-records/srv.md)
- [URI record](https://lemon.domains/dns-records/uri.md)

Interactive version with a record checker and live lookup: https://lemon.domains/dns-records/svcb