What Is an SRV Record

Learn how SRV records enable service discovery by specifying host and port information for services. Includes examples for the DNScale dashboard and API.

An SRV (Service) record specifies the location of servers for specific services. Unlike A records that simply map names to IPs, SRV records provide the hostname, port, priority, and weight for a service—enabling sophisticated service discovery and load balancing.

How SRV Records Work

SRV records use a special naming convention:

_service._protocol.domain.    TTL    SRV    priority weight port target

Example:

_sip._tcp.example.com.    3600    SRV    10 60 5060 sipserver.example.com.

This tells clients: "To reach the SIP service over TCP for example.com, connect to sipserver.example.com on port 5060."

Record Components

Component	Description	Example
Service	Service name (prefixed with `_`)	`_sip`, `_xmpp`, `_ldap`
Protocol	Network protocol (prefixed with `_`)	`_tcp`, `_udp`
Priority	Lower values = higher priority	`10`
Weight	Load distribution among same priority	`60`
Port	TCP/UDP port number	`5060`
Target	Hostname of the server	`sipserver.example.com.`

Common Use Cases

VoIP / SIP

_sip._tcp.example.com.     3600    SRV    10 100 5060 sip1.example.com.
_sip._tcp.example.com.     3600    SRV    20 100 5060 sip2.example.com.
_sip._udp.example.com.     3600    SRV    10 100 5060 sip1.example.com.

XMPP (Jabber) Messaging

_xmpp-client._tcp.example.com.    3600    SRV    5 0 5222 xmpp.example.com.
_xmpp-server._tcp.example.com.    3600    SRV    5 0 5269 xmpp.example.com.

Microsoft 365 / Teams

_sipfederationtls._tcp.example.com.    3600    SRV    100 1 5061 sipfed.online.lync.com.
_sip._tls.example.com.                 3600    SRV    100 1 443 sipdir.online.lync.com.

LDAP Directory Services

_ldap._tcp.example.com.        3600    SRV    0 100 389 ldap.example.com.
_ldaps._tcp.example.com.       3600    SRV    0 100 636 ldap.example.com.
_ldap._tcp.dc._msdcs.example.com.  3600    SRV    0 100 389 dc1.example.com.

CalDAV / CardDAV

_caldav._tcp.example.com.      3600    SRV    0 0 80 calendar.example.com.
_caldavs._tcp.example.com.     3600    SRV    0 0 443 calendar.example.com.
_carddav._tcp.example.com.     3600    SRV    0 0 80 contacts.example.com.
_carddavs._tcp.example.com.    3600    SRV    0 0 443 contacts.example.com.

Minecraft Servers

_minecraft._tcp.example.com.    3600    SRV    0 5 25565 mc.example.com.

Matrix/Element Chat

_matrix._tcp.example.com.    3600    SRV    10 0 8448 matrix.example.com.

Priority and Weight Explained

Priority (Preference)

Lower values are tried first:

_sip._tcp.example.com.    SRV    10 50 5060 primary.example.com.
_sip._tcp.example.com.    SRV    20 50 5060 backup.example.com.

Clients try primary.example.com first (priority 10), then backup.example.com (priority 20) if the primary fails.

Weight (Load Distribution)

Among servers with the same priority, weight determines distribution:

_sip._tcp.example.com.    SRV    10 70 5060 server1.example.com.
_sip._tcp.example.com.    SRV    10 30 5060 server2.example.com.

Server1 receives ~70% of traffic, server2 receives ~30%.

Record Format

Field	Description	Example
Name	`_service._protocol.domain`	`_sip._tcp.example.com`
Type	Record type	`SRV`
Priority	Server preference (lower = preferred)	`10`
Weight	Load balancing weight	`50`
Port	Service port	`5060`
Content	Target hostname	`sipserver.example.com.`
TTL	Time to live (seconds)	`3600`

Adding an SRV Record

Using the Dashboard

Navigate to your zone in the DNScale dashboard
Click Add Record
Configure the record:
- Name: Enter _service._protocol (e.g., _sip._tcp)
- Type: Select SRV
- Priority: Set priority value (e.g., 10)
- Weight: Set weight value (e.g., 50)
- Port: Set the service port (e.g., 5060)
- Value: Enter the target hostname
- TTL: Set the cache duration (default: 3600)
Click Create Record

Using the API

Create an SRV record:

curl -X POST "https://api.dnscale.eu/v1/zones/{zone_id}/records" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "_sip._tcp",
    "type": "SRV",
    "content": "sipserver.example.com",
    "ttl": 3600,
    "priority": 10,
    "weight": 50,
    "port": 5060
  }'

Set up XMPP records:

# Client connections
curl -X POST "https://api.dnscale.eu/v1/zones/{zone_id}/records" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "_xmpp-client._tcp",
    "type": "SRV",
    "content": "xmpp.example.com",
    "ttl": 3600,
    "priority": 5,
    "weight": 0,
    "port": 5222
  }'
 
# Server-to-server federation
curl -X POST "https://api.dnscale.eu/v1/zones/{zone_id}/records" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "_xmpp-server._tcp",
    "type": "SRV",
    "content": "xmpp.example.com",
    "ttl": 3600,
    "priority": 5,
    "weight": 0,
    "port": 5269
  }'

API Response:

{
  "status": "success",
  "data": {
    "message": "Record created successfully",
    "record": {
      "id": "encoded-record-id",
      "name": "_sip._tcp.example.com.",
      "type": "SRV",
      "content": "10 50 5060 sipserver.example.com.",
      "ttl": 3600,
      "disabled": false
    }
  }
}

Best Practices

Use meaningful priorities - Keep gaps between priority values (10, 20, 30) for future flexibility
Target must have A/AAAA records - SRV targets should resolve to IP addresses, not CNAMEs
Use weight for load balancing - Distribute traffic among same-priority servers using weight
Don't use port 0 - A weight of 0 means the server should be used as a last resort
Test with applications - Not all applications respect SRV records; verify with your specific software

Disabling a Service

To indicate a service is not available, use a target of .:

_sip._tcp.example.com.    3600    SRV    0 0 0 .

Testing SRV Records

Verify your SRV records with dig:

dig SRV _sip._tcp.example.com
 
# With full output
dig SRV _xmpp-client._tcp.example.com +short

A - IPv4 address for the target server
AAAA - IPv6 address for the target server
HTTPS - Modern service binding for HTTPS
SVCB - General service binding

Conclusion

SRV records are essential for service discovery, enabling applications to automatically find the right servers, ports, and failover options. They're critical for VoIP, instant messaging, and many enterprise protocols. DNScale's support for SRV records lets you configure sophisticated service architectures with priority-based failover and weighted load balancing.