What Is an SRV Record?
Understanding SRV (Service) records and service discovery
Table of Contents
What Is an SRV Record?
An SRV (Service) record is a DNS record that specifies the location of services (servers) for a domain. SRV records enable service discovery by providing hostname, port, priority, and weight information for services.
SRV records follow the format: _service._protocol.domain (e.g., _sip._tcp.example.com). SRV records include: priority (lower numbers = higher priority), weight (for load balancing), port (service port number), and target (hostname providing the service).
SRV records are used for: SIP (VoIP), XMPP (chat), LDAP, and other service discovery protocols. Check SRV records to verify service location and configuration. Learn more about DNS.
SRV Record Purpose
Service Discovery
SRV records enable service discovery by providing service location information (hostname, port) for applications.
Service Location
SRV records specify where services are located, including hostname and port number information.
Load Balancing
SRV records support load balancing through priority and weight values, distributing service requests across multiple servers.
Service Redundancy
Multiple SRV records with different priorities provide service redundancy, ensuring availability even if primary servers fail.
Protocol Flexibility
SRV records support different protocols (TCP, UDP) and services, providing flexible service configuration.
SRV Record Format
Record Format
SRV records follow this format: priority weight port target
Example SRV Record
_sip._tcp.example.com. 10 60 5060 sip.example.com.
- Priority: 10 (lower = higher priority)
- Weight: 60 (for load balancing)
- Port: 5060 (service port)
- Target: sip.example.com (hostname)
Service Name Format
SRV records use format: _service._protocol.domain
_sip._tcp- SIP over TCP_xmpp._tcp- XMPP over TCP_ldap._tcp- LDAP over TCP
Target Hostname
Target hostname must resolve to an A or AAAA record (IP address), not a CNAME record.
SRV Priority and Weight
Priority
Priority values range from 0 to 65535. Lower numbers indicate higher priority. Clients attempt connections to lower priority servers first.
Weight
Weight values range from 0 to 65535. Used for load balancing among servers with the same priority. Higher weight = more traffic.
Priority Selection
Clients select servers based on priority first, then use weight for load balancing among servers with the same priority.
Load Balancing Example
Multiple SRV records with same priority but different weights enable weighted load balancing:
10 60 5060 server1.example.com- 60% of traffic10 40 5060 server2.example.com- 40% of traffic
Failover
Different priorities enable failover: clients try lower priority servers if higher priority servers are unavailable.
SRV Record Uses
1. SIP (VoIP)
SRV records for SIP: _sip._tcp.example.com - Specifies SIP server location for VoIP services.
2. XMPP (Chat)
SRV records for XMPP: _xmpp-client._tcp.example.com - Specifies XMPP server location for chat services.
3. LDAP
SRV records for LDAP: _ldap._tcp.example.com - Specifies LDAP server location for directory services.
4. Microsoft Services
SRV records for Microsoft services: _autodiscover._tcp.example.com - Specifies Autodiscover service location.
5. Custom Services
SRV records can be used for any service discovery protocol requiring hostname and port information.
