SRV记录和活动目录

任何关于DNS和Active Directory的讨论都必须很快地涉及到AD的“路标”，即SRV(服务定位器)记录。SRV只是另一种资源记录类型，就像A、PTR和MX。它在RFC 2782文档中定义，声明“SRV RR允许管理员为单个域使用多个服务器，轻松地将服务从一个主机移动到另一个主机，并指定一些主机作为服务的主服务器，其他主机作为备份服务器。”Microsoft决定使用SRV记录作为客户端查找域控制器过程的关键部分。那么这些记录从何而来呢?当域控制器启动时，它们通过NetLogon服务向DNS注册。实际上有相当多的这些记录，但现在我们只看其中的两个，它们与域控制器有关。格式如下:_ldap._tcp.dc._msdcs。dnsdomainname _ldap._tcp.sitename._sites.dc._msdcs。因此，属于特定域的工作站可以发送一个DNS查询，查询上面列出的第一种格式的记录。(工作站知道它所在的域，也知道首选DNS服务器在哪里。) Of course, the problem with this scheme is that the domain controller address returned by DNS might or might not be in the same site as the querying workstation. And that’s where the second format listed above comes into play. After talking to a DC in a different site, that DC will reply to the workstation with the name of the site that that workstation is in. Now that the workstation knows its site location in AD, the client will use the second listed format to make another query to DNS, but this time specifying the site name in addition to the domain name. In this way, the workstation learns of a DC that’s nearby as opposed to one that might be on the other side of the planet.