BRev SVCB record — general service binding
SVCB is the generic service-binding record, and the HTTPS record is simply its web-specific profile. Where SRV gave you a host and a port, SVCB carries an extensible set of parameters — protocols, port, address hints, ECH keys, and whatever future keys get registered — so a client can learn how to connect, not merely where.
It has two modes, decided by the priority field. Priority 0 is AliasMode: the record points at another name and the client resolves that instead, which is the apex-friendly aliasing capability. Any non-zero priority is ServiceMode: the record itself carries the parameters, and several records let a client choose between endpoints in preference order.
The visible use today is discovery of encrypted DNS. RFC 9462 defines Discovery of Designated Resolvers using SVCB records under _dns.resolver.arpa, which is how a client learns that its resolver also offers DNS-over-HTTPS or DNS-over-TLS and upgrades to it automatically. Unlike the HTTPS record, SVCB names use the _service._proto prefix convention, because the record has to say which protocol it describes.
What a SVCB record looks like
Type 64 · General service binding. Zone-file form below — owner name, TTL, then the record and its RDATA.
| Name | TTL | Record | What it means |
|---|---|---|---|
| _dns.example.net. | 3600 | SVCB 1 dns.example.net. alpn="h2" dohpath="/dns-query{?dns}" | Advertising a DNS-over-HTTPS endpoint — the RFC 9462 discovery pattern. |
| _8443._foo.example.com. | 3600 | SVCB 1 svc.example.net. port=8443 alpn="foo" | ServiceMode: parameters for a non-HTTP protocol on a non-default port. |
| svc.example.com. | 3600 | SVCB 0 backend.provider.net. | AliasMode (priority 0): resolve the target instead. Legal at an apex, unlike a CNAME. |
The mistakes that break production
Using SVCB where an HTTPS record is expected
Browsers query type 65 (HTTPS) for web origins and do not look up SVCB for them. Publishing the parameters as SVCB on the same name achieves nothing for a browser — use HTTPS for web, SVCB for other protocols.
Mixing AliasMode and ServiceMode carelessly
Priority 0 means “go and resolve the target”; anything else means “here are the parameters”. Publishing an AliasMode record alongside ServiceMode records for the same name is contradictory, and client behaviour is not something to guess at.
Query a SVCB record now
The box below is seeded with cloudflare.com. Choose SVCB as the type and press Look up — the query goes from your browser straight to Cloudflare or Google over DNS-over-HTTPS, with no server of ours in the path.
DNS is the internet's address book: it turns a name like example.com into the addresses and service endpoints machines actually connect to. Every record has a type (what kind of fact it states) and a TTL (how long resolvers may cache it).
Record types
| Type | What it stores |
|---|---|
| A | IPv4 address |
| AAAA | IPv6 address |
| CNAME | Canonical name (alias) |
| MX | Mail exchanger (priority target) |
| TXT | Text — SPF, verifications, DKIM, arbitrary data |
| NS | Authoritative nameservers |
| SOA | Start of authority (serial, refresh, retry, expire, minimum) |
| SRV | Service locator (priority weight port target) |
| CAA | Which CAs may issue certificates |
| PTR | Reverse DNS (IP → name) |
| DNSKEY | DNSSEC public key |
| DS | Delegation signer (DNSSEC chain of trust) |
| HTTPS | HTTPS service binding (ALPN, ECH, hints) |
| SVCB | General service binding |
| TLSA | DANE — pin certificates in DNS |
| NAPTR | Name authority pointer (SIP/ENUM) |
TTL & “propagation”
DNS changes don't “push” anywhere — resolvers simply keep the old answer until its TTL runs out, then fetch the new one. So a change “propagates” in at most the old record's TTL. Planning a change? Lower the TTL (e.g. to 300s) a day in advance, make the change, then raise it back. The compare card above shows whether major public caches have picked your change up yet.
FAQ
What is the difference between SVCB and SRV?
SRV gives a host and a port and nothing else. SVCB carries an extensible parameter set — protocols, port, address hints, ECH keys — and supports aliasing, so it can express things SRV never could.
Should I publish SVCB records for my website?
No — use the HTTPS record (type 65) for web origins, which is the profile browsers actually query. SVCB is for other protocols and for discovery mechanisms such as designated resolvers.
What is AliasMode?
An SVCB record with priority 0, which points the name at another target for the client to resolve. It is CNAME-like but legal at an apex, because it does not exclude other records on the name.