What is a SRV record?

A SRV (Service) record specifies the hostname and port for specific services. It enables service discovery, allowing clients to find servers for services like SIP, XMPP, LDAP, and Microsoft Active Directory without hardcoding server addresses.

What is the SRV record format?

SRV records use the format _service._protocol.domain with fields for priority, weight, port, and target hostname. Example: _sip._tcp.example.com SRV 10 5 5060 sipserver.example.com.

How do priority and weight work in SRV records?

Priority determines which server to try first (lower values preferred). Weight provides load balancing among servers with the same priority—higher weight servers receive more connections proportionally.

What services commonly use SRV records?

Common services include Microsoft Active Directory (_ldap._tcp), SIP/VoIP (_sip._tcp), XMPP/Jabber (_xmpp-client._tcp), Minecraft (_minecraft._tcp), and CalDAV/CardDAV calendar services.

SRV Record Service

The SRV record (Service record) specifies the location of servers for specific services. It allows you to define not just the hostname, but also the port, priority, and weight for load balancing. SRV records are commonly used for VoIP, XMPP, LDAP, and Microsoft services.

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What Is an SRV Record?

SRV records enable service discovery by specifying which server handles a particular service for a domain. Unlike A records which simply map domains to IPs, SRV records provide:

Service type — What service (e.g., SIP, XMPP, LDAP)
Protocol — TCP or UDP
Port number — Where the service listens
Priority — Which server to try first
Weight — Load balancing within same priority
Target — The server hostname

SRV Record Format

SRV records follow a specific naming convention:

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

Example SRV Record

_sip._tcp.example.com.  3600  IN  SRV  10  60  5060  sip1.example.com.
_sip._tcp.example.com.  3600  IN  SRV  10  40  5060  sip2.example.com.
_sip._tcp.example.com.  3600  IN  SRV  20  0   5060  backup.example.com.

SIP traffic uses sip1 (60%) and sip2 (40%) as primaries, with backup as failover.

SRV Record Fields

Field	Description	Example
_service	Service name (preceded by underscore)	_sip, _xmpp, _ldap
_protocol	Protocol (TCP or UDP)	_tcp, _udp
Priority	Lower = higher priority (like MX)	10, 20, 30
Weight	Load balancing within same priority	60, 40 (60%/40% split)
Port	Service port number	5060, 5222, 443
Target	Server hostname	server.example.com.

Priority and Weight

Priority

Like MX records, lower numbers are tried first. If priority 10 servers are unavailable, try priority 20.

Weight

Within the same priority, weight distributes traffic proportionally. A server with weight 60 gets 3× the traffic of one with weight 20.

_sip._tcp.example.com.  SRV  10  60  5060  server1.example.com.  ; 60%
_sip._tcp.example.com.  SRV  10  20  5060  server2.example.com.  ; 20%
_sip._tcp.example.com.  SRV  10  20  5060  server3.example.com.  ; 20%

Common SRV Record Examples

Microsoft 365 / Exchange

_autodiscover._tcp.example.com.  SRV  0  0  443  autodiscover.outlook.com.
_sip._tls.example.com.           SRV  100  1  443  sipdir.online.lync.com.
_sipfederationtls._tcp.example.com.  SRV  100  1  5061  sipfed.online.lync.com.

XMPP (Jabber)

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

SIP (VoIP)

_sip._udp.example.com.  SRV  10  100  5060  sip.example.com.
_sip._tcp.example.com.  SRV  10  100  5060  sip.example.com.

LDAP

_ldap._tcp.example.com.  SRV  0  100  389  ldap.example.com.
_ldaps._tcp.example.com. SRV  0  100  636  ldap.example.com.

CalDAV / CardDAV

_caldavs._tcp.example.com.  SRV  0  1  443  calendar.example.com.
_carddavs._tcp.example.com. SRV  0  1  443  contacts.example.com.

Disabling a Service

To explicitly indicate a service is not available, use a "." as the target:

_xmpp-client._tcp.example.com.  SRV  0  0  0  .

SRV Record Best Practices

Use appropriate priority levels — Reserve lower numbers for primary servers.
Balance with weights — Use weights to distribute load among same-priority servers.
Target must have A/AAAA records — The target hostname needs address records.
Don't use CNAMEs as targets — SRV targets should resolve directly to A/AAAA records.
Include both TCP and UDP — Some services need records for both protocols.
Test service discovery — Verify clients can discover your services via SRV.

Querying SRV Records

# Using dig
dig _sip._tcp.example.com SRV

# Using host
host -t SRV _sip._tcp.example.com

# Using nslookup
nslookup -type=SRV _sip._tcp.example.com

Troubleshooting SRV Records

Common issues and solutions:

Service not connecting — Verify the SRV record exists with correct service and protocol names.
Underscore issues — Service and protocol must be prefixed with underscore (_sip, _tcp).
Target not resolving — The target hostname needs A or AAAA records.
Port unreachable — Verify the specified port is open and the service is listening.
Weight not distributing correctly — Weight is a hint; clients may implement it differently.

Check Your SRV Records

Use our DNS Record Finder to look up SRV records for any domain.