问题：
1：ISTG是什么？
2：如何确定ISTG角色?
3：ISTG有什么作用？
4：如何在ISTG上运行KCC，生成站点间的拓扑。
问题1：ISTG是什么？
Applies To: Windows Server 2008, Windows Server 2008 R2
The Intersite Topology Generator (ISTG) is the domain controller in each site that is responsible for generating the intersite topology. （站点间拓扑生成器ISTG是在每个站点的一台域控制器，其负责生成站点间的拓扑）。这里说明ISTG的作用之一是负责生成站点间的拓扑。但是有是人说KCC才负责生成站点间的拓扑，这样的说法其实也可以，因为我们要在ISTG的域控制器上运行KCC，才会生成站点间的复制拓扑，正如问题2中描述的那样，If you want to regenerate the intersite topology, you must determine the identity of the ISTG role owner in a site.
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问题2：如何确定ISTG角色?
If you want to regenerate the intersite topology, you must determine the identity of the ISTG role owner in a site. （如果你想生成站点间拓扑，你必须在站点中确定ISTG角色持有者的身份）。
You can use this procedure to view the NTDS Site Settings object properties and determine the ISTG role owner for the site.
（你可以使用这个步骤查看NTDS Site Settings 对象属性，确定站点中ISTG角色的持有者）
Membership in Domain Users, or equivalent, is the minimum required to complete this procedure. Review details about using the appropriate accounts and group memberships at Local and Domain Default Groups (http://go.microsoft.com/fwlink/?LinkId=83477).
To determine the ISTG role owner for a site
- Open Active Directory Sites and Services: On the Start menu, point to Administrative Tools, and then click Active Directory Sites and Services.
- In the console tree, click the site object whose ISTG role owner you want to determine.
- In the details pane, right-click the NTDS Site Settings object, and then click Properties. The current role owner appears in the Server box under Inter-Site Topology Generator.
我们还可以使用Repadmin命令显示站点中拥有ISTG角色的域控制器，Repadmin /?只是显示一些基本的命令，而Repadmin /experthelp,才会显示高级命令的帮助
命令查看持有ISTG角色的域控制器
问题1和问题2均来自：https://technet.microsoft.com/en-us/library/cc794776(v=ws.10).aspx
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问题3：ISTG有什么作用？
ISTG is used for replication between sites ie intersite replication . it selects the bridge head server automatically which willl be authorised to replicate information to other bridge head server of other site. If the bridge head server goes down then due to ISTG a new server takes its place and administrator need not to intervene and there is no problem in replication.
ISTG用于两个站点间复制，即站点间复制。ISTG自动选择桥头服务器，其（挑选是桥头服务器）会被授予复制信息到其它站点的的桥头服务器。如果桥头服务器出现故障，那么由于ISTG一个新的服务器会接替这台桥头服务器，管理员不需要干预，复制方面不会出现问题。
问题3来自：http://www.answers.com/Q/What_does_ISTG_do_in_active_directory
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问题4：如何在ISTG上运行KCC，生成站点间的拓扑。
Generate the Replication Topology on the ISTG
Applies To: Windows Server 2008, Windows Server 2008 R2
You can use this procedure to generate the intersite replication topology on the intersite topology generator (ISTG). The Knowledge Consistency Checker (KCC) generates the Active Directory replication topology on every domain controller. The KCC runs by default every 15 minutes.
You can force the KCC to run on any domain controller. The topology that is generated depends on the domain controller on which you run the command. You can force the KCC to run as follows:
- To generate the intersite replication topology, run the KCC on the domain controller in the site that holds the ISTG role.（在站点中持有ISTG角色的域控制器上运行KCC，生成站点间的复制拓扑）
- To generate the intrasite replication topology, run the KCC on any domain controller in the site that does not hold the ISTG role.（在站点中非ISTG角色持有者的域控制器上运行KCC，生成站点内的复制拓扑）
To generate the replication topology on the ISTG, you must first complete the procedure: Determine the ISTG Role Owner for a Site.
Membership in Enterprise Admins, or equivalent, is the minimum required to complete this procedure. Review details about using the appropriate accounts and group memberships at Local and Domain Default Groups (http://go.microsoft.com/fwlink/?LinkId=83477).
To generate the replication topology on the ISTG
- Determine the server that holds the ISTG role for the site.
- Open Active Directory Sites and Services: On the Start menu, point to Administrative Tools, and then click Active Directory Sites and Services.
- In the console tree, expand Sites, and then expand the site that contains the ISTG on which you want to run the KCC.
- Expand Servers, and then click the Server object for the ISTG.
- In the details pane, right-click NTDS Settings, click All Tasks, and then click Check Replication Topology.
- In the Check Replication Topology message box, click OK.
问题4来自：https://technet.microsoft.com/en-us/library/cc794953(v=ws.10).aspx