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SRV - Location of Service

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SRV-records are used to specify the location of a service.

They are recently being used in connection with different directory servers such as LDAP (Lightweight Directory Access Protocol), and Windows 2000 directory services.

They can also be used for advanced load balancing and to specify specific ports for services - for example that a web-server is running on port 8080 instead of the usual port 80.

The name of a SRV-record is defined as "_service._protocol.domain" - for example "". Most internet services are defined in RFC1700 (page 15), and the protocol is generally TCP or UDP.

The "service location" is specified through a target, priority, weight, and port:
- Target is the domain name of the server (referencing an A-record).
- Priority is a preference number used when more servers are providing the same service (lower numbers are tried first).
- Weight is used for advanced load balancing.
- Port is the TCP/UDP port number on the server that provides this service.

The format in which to enter the data is as follows:

_ftp._tcp SRV 10 0 8080

Where _ftp._tcp is the subdomain for the root zone name, 10 is priority, 0 is the weight, 8080 is the port and is the host.

Here is an example for setting up Microsoft Office365.

_sip._tls SRV 100 1 443
_sipfederationtls._tcp SRV 100 1 5061

Please note that Office365 also needs these 2 CNAME records:

lyncdiscover CNAME

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