This article covers DNS records of the SRV and NAPTR types in detail. For general instructions on DNS records and how to set them up in the Customer Administration, see the article DNS – Domain Records.
In this article, you will learn:
- What SRV records are used for
- How to enter SRV records correctly
- Examples of SRV record settings
- How the NAPTR record works
- Frequently Asked Questions
Purpose of SRV records
The Service (SRV) record is used to specify information about the services available on a host. These services commonly include, for example, XMPP (an instant messaging protocol), SIP (a signalling protocol for internet telephony), or LDAP (a protocol for storing and accessing data on a directory server).
An SRV record cannot be used to specify the port on which a service runs if that service does not support this type of record.
For example, if you want to run a website (HTTP or HTTPS protocol) on a port other than the standard one, you must configure this on the server. You cannot set this port in a record of type A, AAAA you cannot set this port with SRV either.
Entering SRV records
SRV records usually have a specific format for both the name and the data.
SRV record name
The symbolic name of an SRV record usually has the form _service._protocol, for example _sip._udp.
If needed, add a subdomain to the end of this symbolic name, for example _ldap._tcp.subdom.
SRV record data
The data of an SRV record consists of the following parts:
- Priority: a positive number that determines which record is evaluated first (the one with the lowest number); the system evaluates the other records only if the priority service is unavailable.
- Weight: a relative weight for records with the same priority, used for load balancing.
- Port: the TCP or UDP port on which the service listens.
- Target: The hostname of the server providing the service.
When filling in an SRV record, follow these rules:
- Assign the lowest priority number but the highest weight to the main server.
- Enter the hostname in the form of a domain, not an IP address.
A general SRV record therefore looks like this:
Name TTL Type Data (symbolic name) 300 SRV (priority) (weight) (port) (hostname)
Examples of SRV records
Example: An SRV record for SIP over TCP on port 5060 with the target tel.wds-test.cz.
NAPTR Record
The Name Authority Pointer (NAPTR) record is often used in combination with SRV records, most commonly for internet telephony to map the SIP protocol. When entering it, follow the instructions of your service provider.
Frequently Asked Questions
How do I make DNS point HTTP to a port other than 80 (or 443 for HTTPS)?
You cannot configure this in DNS; you must set it up on the server.