What is a DNS SRV record?
The DNS "service" (SRV) record specifies a host and port for specific services such as Voice over IP (VoIP), instant messaging, and more. While most DNS records only specify a server or an IP address, SRV records are unique because they include a port at that IP address as well.
Certain Internet protocols require the use of SRV records to function correctly.
What is a Port?
In networking, ports are virtual places that designate which processes network traffic should go to within a computer. Ports allow computers to differentiate between different types of traffic:
- VoIP streams go to a different port than email messages, even if they arrive over the same internet connection.
- Just like IP addresses, all ports are assigned a specific number.
Protocols such as IMAP, SIP, and XMPP need to connect to a specific port in addition to a specific server. SRV records are the mechanism used to specify these ports within the DNS.
[Image of network ports and protocols mapping]
What goes in an SRV record?
An SRV record contains several fields of information. Below is a breakdown of the components:
| Field | Example Value | Description |
|---|---|---|
| Service | XMPP | The symbolic name of the desired service. |
| Proto | TCP | The transport protocol (usually TCP or UDP). |
| Name | example.com | The domain name to which this record refers. |
| TTL | 86400 | Time to Live (in seconds). |
| Class | IN | Internet class (standard). |
| Type | SRV | Record type. |
| Priority | 10 | Priority of the target host. |
| Weight | 5 | Relative weight for records with the same priority. |
| Port | 5223 | The TCP or UDP port on which the service is found. |
| Target | server.example.com | The canonical hostname of the machine providing the service. |
Standard Format
SRV records are formatted in this specific sequence:
_service._proto.name. TTL class type priority weight port target.
Actual Example:
_xmpp._tcp.example.com. 86400 IN SRV 10 5 5223 server.example.com.
Note: SRV records must point directly to an A record or an AAAA record. The target cannot be a CNAME.
Priority vs. Weight: Understanding the Difference
SRV records allow administrators to balance traffic across multiple servers using two values: Priority and Weight.
[Image of DNS load balancing using SRV priority and weight]
1. Priority (Looked at first)
The server with the lower priority value is tried first.
- Example: If Server A has priority 10 and Server B has priority 20, the service will always query Server A first.
2. Weight (Tie-breaker)
Weight is used to distribute traffic among servers with the same priority.
- Example: If Servers A, B, and C all have priority 10, but Server A has a weight of 5, Server B has 3, and Server C has 2:
- Server A will receive approximately 50% of the traffic.
- Server B will receive 30%.
- Server C will receive 20%.
Optimizing Modern Communications
In 2026, SRV records are critical for businesses using integrated communication suites and VoIP. Ensuring these records are accurately configured is a hallmark of a Reliable Email Provider and a robust digital infrastructure, especially for companies scaling across global markets.
Would you like me to help you generate a specific SRV record for a service like Microsoft Teams or a custom SIP provider?