What is a SVCB record?

A SVCB (Service Binding) record is a generic DNS record type (type 64) that provides connection parameters for any service. It's the foundation for service-specific records like HTTPS, enabling service discovery and connection optimization.

What's the difference between SVCB and HTTPS records?

HTTPS records (type 65) are SVCB records specifically for the HTTPS scheme. SVCB is the generic form that can be used for any scheme. For web services, use HTTPS records; for other protocols, use SVCB with the scheme prefix.

How do SVCB record priorities work?

Priority 0 is AliasMode, redirecting to another name. Priority 1+ is ServiceMode, providing actual parameters. Lower non-zero priorities are preferred. Clients try servers in priority order, falling back to higher values.

Can SVCB records replace SRV records?

SVCB is more flexible than SRV, supporting protocol-specific parameters like ALPN and ECH. However, SRV remains widely used. New protocols should consider SVCB, while existing SRV-based systems continue to work.

SVCB Record Service

The SVCB record (Service Binding) is a general-purpose DNS record type that provides connection information for any service. It's the generic version of the HTTPS record, allowing service-specific connection parameters to be published in DNS.

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What Is an SVCB Record?

SVCB records (RFC 9460) provide a flexible way to specify connection information for services. They can include:

Target hostname for the service
Priority for load balancing and failover
Service parameters (port, protocol, IP hints, etc.)
Aliasing to another domain (like CNAME but more flexible)

SVCB Record Format

Example SVCB Record

_myservice._tcp.example.com.    3600    IN    SVCB    1 server.example.com. port=8443 alpn=h2

SVCB Record Fields

Field	Description	Example
Priority	0 = alias, >0 = service mode	1, 10, 0
Target	Target hostname (. = self)	server.example.com.
Parameters	Service-specific key-value pairs	port=8443 alpn=h2

Common Service Parameters

Parameter	Description	Example
`alpn`	Application protocols	alpn=h2,h3
`port`	TCP/UDP port	port=8443
`ipv4hint`	IPv4 address hints	ipv4hint=192.0.2.1
`ipv6hint`	IPv6 address hints	ipv6hint=2001:db8::1
`ech`	Encrypted Client Hello	ech=base64data
`mandatory`	Required parameters	mandatory=alpn

Service Mode vs Alias Mode

Service Mode (Priority > 0)

Provides direct connection information:

_myservice._tcp.example.com.    SVCB    1 server.example.com. port=9000

Alias Mode (Priority = 0)

Redirects to another domain (like CNAME):

_myservice._tcp.example.com.    SVCB    0 other.example.net.

SVCB vs SRV Records

Aspect	SVCB	SRV
Parameters	Extensible key-value	Fixed (priority, weight, port)
IP hints	Supported	No
ALPN	Supported	No
Alias mode	Yes (priority 0)	No
Maturity	Newer (2023)	Established (2000)

SVCB Best Practices

Use for modern services — SVCB is ideal for services needing rich connection hints.
Include IP hints — Reduce additional DNS lookups.
Specify ALPN — Help clients choose the right protocol.
Keep A/AAAA records — For backward compatibility.
Test client support — SVCB is relatively new; verify compatibility.

Common Use Cases

Custom Application Protocol

_myapp._tcp.example.com.    SVCB    1 . alpn=myprotocol port=5000

Multiple Priorities

_api._tcp.example.com.    SVCB    1 primary.example.com. port=443
_api._tcp.example.com.    SVCB    2 backup.example.com. port=443

Troubleshooting SVCB

Common issues and solutions:

Record not found — Ensure DNS provider supports SVCB record type.
Client not using hints — SVCB is relatively new; verify client support.
Target not resolving — Target hostname needs A/AAAA records.
Invalid parameters — Check parameter syntax carefully.

Check Your SVCB Records

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