RFC2782: DNS SRV
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* February 2000
* Category: Standards Track
* Obsoletes: 2052
* Company::

    * Microsoft Corp.
    * Troll Technologies
    * Internet Software Consortium

* SRV 记录是 DNS 服务器的数据库中支持的一种资源记录的类型，它记录了哪台计算机提供了哪个服务这么一个简单的信息。



The format of the SRV RR::

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

SRV RR字段说明::

    Service: 
        The symbolic name of the desired service, as defined in Assigned Numbers [STD 2] or locally.

    Proto: 
        The symbolic name of the desired protocol
        _TCP and _UDP are at present the most useful values for this field

    Name:
        The domain this RR refers to.

    TTL:
        Standard DNS meaning [RFC 1035].

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

    Priority:
        The priority of this target host.
        The range is 0-65535.

    Weight:
        A server selection mechanism.

    Port:
        The port on this target host of this service.

    Target:
        The domain name of the target host.
        There MUST be one or more address records for this name, the name MUST NOT be an alias
        A Target of "." means that the service is decidedly not available at this domain.

SRV 格式::

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


Fictional example::
    
    This example uses fictional service "foobar" as an aid in understanding SRV records. 

      $ORIGIN example.com.
      @               SOA server.example.com. root.example.com. ( 1995032001 3600 3600 604800 86400 )
                      NS  server.example.com.
                      NS  ns1.ip-provider.net.
                      NS  ns2.ip-provider.net.

      ; foobar - use old-slow-box or new-fast-box if either is
      ; available, make three quarters of the logins go to
      ; new-fast-box.
      _foobar._tcp     SRV 0 1 9 old-slow-box.example.com.
                       SRV 0 3 9 new-fast-box.example.com.

      ; if neither old-slow-box or new-fast-box is up, switch to
      ; using the sysdmin's box and the server
                       SRV 1 0 9 sysadmins-box.example.com.
                       SRV 1 0 9 server.example.com.

      server           A   172.30.79.10
      old-slow-box     A   172.30.79.11
      sysadmins-box    A   172.30.79.12
      new-fast-box     A   172.30.79.13

      ; NO other services are supported
      *._tcp          SRV  0 0 0 .
      *._udp          SRV  0 0 0 .