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1. Introduction and Overview

1.1 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 backups.

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

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

1.2 Definitions​

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.

1.3 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.

Specification Requirements

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.

1.4 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:

_ldap._tcp.example.com

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

LDAP Example Disclaimer

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.

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