RFC2782: DNS SRV¶

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 .