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SRV Records (view source)

Revision as of 03:26, 19 April 2013

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A Service record (SRV record) is a specification of data in the Domain Name System (DNS) defining the location, i.e. the hostname and port number, of servers for specified services. It is defined in [http://tools.ietf.org/html/rfc2782 RFC 2782].
A Service record ('''SRV record''') is a specification of data in the Domain Name System ('''DNS''') defining the location (i.e. the hostname and port number) of servers for specified services. It is defined in [http://tools.ietf.org/html/rfc2782 RFC 2782].


XMPP often require SRV support by network elements.
== Ports ==
=== Very important ===
* <span style="color:#FF0000">XMPP uses 5222 ('''C2S''') and 5269 ('''S2S''') ports in TCP only ([http://xmpp.org/rfcs/rfc6120.html RFC 6120]).</span>
=== If used ===
* STUN uses 3478 port in TCP/UDP and STUNS (STUN over TLS) uses 5349 port in TCP only ([http://tools.ietf.org/html/rfc5389 RFC 5389]).
* TURN uses 3478 port in TCP/UDP and TURNS (TURN over TLS) uses 5349 port in TCP only ([http://tools.ietf.org/html/rfc5766 RFC 5766], [http://tools.ietf.org/html/rfc5928 RFC 5928]).


== Record format ==
== Record format ==
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  _service._proto.name TTL class SRV priority weight port target
  _service._proto.name TTL class SRV priority weight port target


* ''service'': the symbolic name of the desired service.
* '''service''': the symbolic name of the desired service.
* ''proto'': the transport protocol of the desired service; this is usually either TCP or UDP.
* '''proto''': the transport protocol of the desired service; this is usually either TCP or UDP.
* ''name'': the domain name for which this record is valid.
* '''name''': the domain name for which this record is valid.
* ''TTL'': standard DNS time to live field.
* '''TTL''': standard DNS time to live field.
* ''class'': standard DNS class field (this is always ''IN'').
* '''class''': standard DNS class field (this is always '''IN''').
* ''priority'': the priority of the target host, lower value means more preferred.
* '''priority''': the priority of the target host, lower value means more preferred.
* ''weight'': A relative weight for records with the same priority.
* '''weight''': A relative weight for records with the same priority.
* ''port'': the TCP or UDP port on which the service is to be found.
* '''port''': the TCP or UDP port on which the service is to be found.
* ''target'': the canonical hostname of the machine providing the service.
* '''target''': the canonical hostname of the machine providing the service.


== XMPP SRV records ==
== XMPP SRV records ==
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  _xmpp-server._tcp.example.net. 86400 IN SRV 15 0 5269 backup.example.net.
  _xmpp-server._tcp.example.net. 86400 IN SRV 15 0 5269 backup.example.net.


The XMPP domain is example.net and the principal server is server1.example.net which used 50% after server2.example.net 30%, server3.example.net 10%, server4.example.net 10% too, if server 1 is down, server2, server3 and server4 will work, if servers 1/2/3/4 are down, backup will work.
The XMPP domain is example.net and the principal server is server1.example.net which used 50% after server2.example.net 30%, server3.example.net 10%, server4.example.net 10% too, if server1 is down, server2, server3 and server4 will work, if servers 1/2/3/4 are down, backup will work.


== Retrieving SRV records ==
=== Retrieving XMPP SRV records ===
  $ dig SRV _xmpp-client._tcp.example.net
  $ dig SRV _xmpp-client._tcp.example.net
  $ dig SRV _xmpp-server._tcp.example.net
  $ dig SRV _xmpp-server._tcp.example.net
== STUN SRV records ==
_stun._tcp.example.net. TTL IN SRV priority weight port target
_stun._udp.example.net. TTL IN SRV priority weight port target
_stuns._tcp.example.net. TTL IN SRV priority weight port target
=== Example 1 ===
_stun._tcp.example.net. 86400 IN SRV 5 0 3478 example.net.
_stun._udp.example.net. 86400 IN SRV 5 0 3478 example.net.
_stuns._tcp.example.net. 86400 IN SRV 5 0 5349 example.net.
The STUN domain is example.net and the server is example.net.
=== Example 2 ===
_stun._tcp.example.net. 86400 IN SRV 5 0 3478 server.example.net.
_stun._udp.example.net. 86400 IN SRV 5 0 3478 server.example.net.
_stuns._tcp.example.net. 86400 IN SRV 5 0 5349 server.example.net.
The STUN domain is example.net and the server is server.example.net.
=== Example 3 ===
_stun._tcp.example.net. 86400 IN SRV 5 50 3478 server1.example.net.
_stun._tcp.example.net. 86400 IN SRV 10 30 3478 server2.example.net.
_stun._tcp.example.net. 86400 IN SRV 10 10 3478 server3.example.net.
_stun._tcp.example.net. 86400 IN SRV 10 10 3478 server4.example.net.
_stun._tcp.example.net. 86400 IN SRV 15 0 3478 backup.example.net.
_stun._udp.example.net. 86400 IN SRV 5 50 3478 server1.example.net.
_stun._udp.example.net. 86400 IN SRV 10 30 3478 server2.example.net.
_stun._udp.example.net. 86400 IN SRV 10 10 3478 server3.example.net.
_stun._udp.example.net. 86400 IN SRV 10 10 3478 server4.example.net.
_stun._udp.example.net. 86400 IN SRV 15 0 3478 backup.example.net.
_stuns._tcp.example.net. 86400 IN SRV 5 50 5349 server1.example.net.
_stuns._tcp.example.net. 86400 IN SRV 10 30 5349 server2.example.net.
_stuns._tcp.example.net. 86400 IN SRV 10 10 5349 server3.example.net.
_stuns._tcp.example.net. 86400 IN SRV 10 10 5349 server4.example.net.
_stuns._tcp.example.net. 86400 IN SRV 15 0 5349 backup.example.net.
The XMPP domain is example.net and the principal server is server1.example.net which used 50% after server2.example.net 30%, server3.example.net 10%, server4.example.net 10% too, if server1 is down, server2, server3 and server4 will work, if servers 1/2/3/4 are down, backup will work.
=== Retrieving STUN SRV records ===
$ dig SRV _stun._tcp.example.net
$ dig SRV _stun._udp.example.net
$ dig SRV _stuns._tcp.example.net
== TURN SRV records ==
_turn._tcp.example.net. TTL IN SRV priority weight port target
_turn._udp.example.net. TTL IN SRV priority weight port target
_turns._tcp.example.net. TTL IN SRV priority weight port target
=== Example 1 ===
_turn._tcp.example.net. 86400 IN SRV 5 0 3478 example.net.
_turn._udp.example.net. 86400 IN SRV 5 0 3478 example.net.
_turns._tcp.example.net. 86400 IN SRV 5 0 5349 example.net.
The TURN domain is example.net and the server is example.net.
=== Example 2 ===
_turn._tcp.example.net. 86400 IN SRV 5 0 3478 server.example.net.
_turn._udp.example.net. 86400 IN SRV 5 0 3478 server.example.net.
_turns._tcp.example.net. 86400 IN SRV 5 0 5349 server.example.net.
The TURN domain is example.net and the server is server.example.net.
=== Example 3 ===
_turn._tcp.example.net. 86400 IN SRV 5 50 3478 server1.example.net.
_turn._tcp.example.net. 86400 IN SRV 10 30 3478 server2.example.net.
_turn._tcp.example.net. 86400 IN SRV 10 10 3478 server3.example.net.
_turn._tcp.example.net. 86400 IN SRV 10 10 3478 server4.example.net.
_turn._tcp.example.net. 86400 IN SRV 15 0 3478 backup.example.net.
_turn._udp.example.net. 86400 IN SRV 5 50 3478 server1.example.net.
_turn._udp.example.net. 86400 IN SRV 10 30 3478 server2.example.net.
_turn._udp.example.net. 86400 IN SRV 10 10 3478 server3.example.net.
_turn._udp.example.net. 86400 IN SRV 10 10 3478 server4.example.net.
_turn._udp.example.net. 86400 IN SRV 15 0 3478 backup.example.net.
_turns._tcp.example.net. 86400 IN SRV 5 50 5349 server1.example.net.
_turns._tcp.example.net. 86400 IN SRV 10 30 5349 server2.example.net.
_turns._tcp.example.net. 86400 IN SRV 10 10 5349 server3.example.net.
_turns._tcp.example.net. 86400 IN SRV 10 10 5349 server4.example.net.
_turns._tcp.example.net. 86400 IN SRV 15 0 5349 backup.example.net.
The XMPP domain is example.net and the principal server is server1.example.net which used 50% after server2.example.net 30%, server3.example.net 10%, server4.example.net 10% too, if server1 is down, server2, server3 and server4 will work, if servers 1/2/3/4 are down, backup will work.
=== Retrieving TURN SRV records ===
$ dig SRV _turn._tcp.example.net
$ dig SRV _turn._udp.example.net
$ dig SRV _turns._tcp.example.net
== External links ==
* [http://tools.ietf.org/html/rfc2782 RFC 2782: A DNS RR for specifying the location of services (DNS SRV)]
* [http://xmpp.org/rfcs/rfc6120.html RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core]
* [http://tools.ietf.org/html/rfc5389 RFC 5389: Session Traversal Utilities for NAT (STUN)]
* [http://tools.ietf.org/html/rfc5766 RFC 5766: Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)]
* [http://tools.ietf.org/html/rfc5928 RFC 5928: Traversal Using Relays around NAT (TURN) Resolution Mechanism]
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