A DNS RR for specifying the location of services (DNS SRV)
RFC 2782

Document Type RFC - Proposed Standard (February 2000; No errata)
Updated by RFC 8553, RFC 6335
Obsoletes RFC 2052
Authors Arnt Gulbrandsen  , Levon Esibov 
Last updated 2020-07-29
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Network Working Group                                     A. Gulbrandsen
Request for Comments: 2782                            Troll Technologies
Obsoletes: 2052                                                 P. Vixie
Category: Standards Track                   Internet Software Consortium
                                                               L. Esibov
                                                         Microsoft Corp.
                                                           February 2000

       A DNS RR for specifying the location of services (DNS SRV)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.


   This document describes a DNS RR which specifies the location of the
   server(s) for a specific protocol and domain.

Overview and rationale

   Currently, one must either know the exact address of a server to
   contact it, or broadcast a question.

   The SRV RR allows administrators to use several servers for a single
   domain, to move services from host to host with little fuss, and to
   designate some hosts as primary servers for a service and others as

   Clients ask for a specific service/protocol for a specific domain
   (the word domain is used here in the strict RFC 1034 sense), and get
   back the names of any available servers.

   Note that where this document refers to "address records", it means A
   RR's, AAAA RR's, or their most modern equivalent.

Gulbrandsen, et al.         Standards Track                     [Page 1]
RFC 2782                       DNS SRV RR                  February 2000


   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT" and "MAY"
   used in this document are to be interpreted as specified in [BCP 14].
   Other terms used in this document are defined in the DNS
   specification, RFC 1034.

Applicability Statement

   In general, it is expected that SRV records will be used by clients
   for applications where the relevant protocol specification indicates
   that clients should use the SRV record. Such specification MUST
   define the symbolic name to be used in the Service field of the SRV
   record as described below. It also MUST include security
   considerations. Service SRV records SHOULD NOT be used in the absence
   of such specification.

Introductory example

   If a SRV-cognizant LDAP client wants to discover a LDAP server that
   supports TCP protocol and provides LDAP service for the domain
   example.com., it does a lookup of


   as described in [ARM].  The example zone file near the end of this
   memo contains answering RRs for an SRV query.

   Note: LDAP is chosen as an example for illustrative purposes only,
   and the LDAP examples used in this document should not be considered
   a definitive statement on the recommended way for LDAP to use SRV
   records. As described in the earlier applicability section, consult
   the appropriate LDAP documents for the recommended procedures.

The format of the SRV RR

   Here is the format of the SRV RR, whose DNS type code is 33:

        _Service._Proto.Name TTL Class SRV Priority Weight Port Target

        (There is an example near the end of this document.)

        The symbolic name of the desired service, as defined in Assigned
        Numbers [STD 2] or locally.  An underscore (_) is prepended to
        the service identifier to avoid collisions with DNS labels that
        occur in nature.

Gulbrandsen, et al.         Standards Track                     [Page 2]
RFC 2782                       DNS SRV RR                  February 2000

        Some widely used services, notably POP, don't have a single
        universal name.  If Assigned Numbers names the service
        indicated, that name is the only name which is legal for SRV
        lookups.  The Service is case insensitive.

        The symbolic name of the desired protocol, with an underscore
        (_) prepended to prevent collisions with DNS labels that occur
        in nature.  _TCP and _UDP are at present the most useful values
        for this field, though any name defined by Assigned Numbers or
        locally may be used (as for Service).  The Proto is case

        The domain this RR refers to.  The SRV RR is unique in that the
        name one searches for is not this name; the example near the end
        shows this clearly.

        Standard DNS meaning [RFC 1035].

        Standard DNS meaning [RFC 1035].   SRV records occur in the IN
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