Active Directory Replication Terminology - Part I

Following is some of the day to day Active Directory terminology.

> BridgeHeads Servers,
A bridgehead is a point at which a connection leaves or enters a site.

> ISTG (Intersite Topology Generator),
The single KCC in a site that manages intersite connection objects for the site.

> KCC (Knowledege Consistency Checker),
The Knowledge Consistency Checker (KCC) is an Active Directory component that is responsible for the generation of the replication topology between domain controllers.

So what is the relation between those three?

Knowledge Consistency Checker (KCC), runs as an application on every domain controller and communicates through the distributed Active Directory database. KCC reads configuration data and reads and writes connection objects.
One domain controller in each site is selected as the Intersite Topology Generator (ISTG). To enable replication across site links, the ISTG automatically designates one or more servers to perform site-to-site replication. These servers are called bridgehead servers.

The ISTG creates a view of the replication topology for all sites, including existing connection objects between all domain controllers that are acting as bridgehead servers. The ISTG then creates inbound connection objects for those servers in its site that it determines will act as bridgehead servers and for which connection objects do not already exist. Thus, the scope of operation for the KCC is the local server only, and the scope of operation for the ISTG is a single site.

For more information please see:
http://technet.microsoft.com/en-us/library/cc755994(WS.10).aspx

How to lock Internet Explorer setting through GPO

To lock changes in Proxy settings using GPO check the following GPO option:
User configuration->Administrative Templates->Windows Components->Internet Explorer->"Disable changing proxy settings"

Set the option ->"Disable changing proxy settings" to enable.

Useful command in managing Active Directory

Here's some of the list that common to use on day to day administration and troubleshooting of Active Directory:

> To summarizes the replication state and health of a forest:
Repadmin /Replsum /BySrc /ByDst

> To show the state of the last inbound replication for specified domain controller:
Repadmin /Showreps
Repadmin /Showrepl

> To show the state of the last inbound and outbound replication (change notification) for specified domain controller:
Repadmin /Showrepl /repsto

> To display the replication queue list:
Repadmin /queue
> To display all the Domain Controller in the forest:
Repadmin /Viewlist *
> To display the Intersite Topology Generator (ISTG) server for specified site:
Repadmin /ISTG
> To display the Bridgeheads servers for specified site:
Repadmin / Bridgeheads

> To synchronize a sepecified domain controller with all of the replication partners
Repadmin /syncall (DC_name) /A /e

> To list the name of Domain Contollers in a domain:
Nltest /dclist:(domainname)

> To verify if we can locate a domain controller:
Nltest /dsgetdc:(domainname)

> To display the servers that hold FSMO role:
Netdom query FSMO

> To chek the health of DNS settings:
DCdiag /test:DNS

> To query the tombstonelifetime setting in a forest:
dsquery * "cn=Directory Service,cn=Windows NT,cn=Services,cn=Configuration,dc=contoso,dc=com" -scope base -attr tombstonelifetime

Site Costed Referrals

Windows Server 2003 and above supports the ability to provide finer control over how DFS referrals are returned for the SYSVOL and NETLOGON shares.

By default, in Windows Server 2003 the DFS referral list will contain all local domain controllers of the client’s domain in the local site, randomly ordered, and then all other domain controllers in the domain randomly ordered.
Defining the SiteCostedReferrals Registry value on the domain controllers will alter the DFS referrals so that all local domain controllers are listed first, randomly ordered, then the “next best” site’s domain controllers, and then all others. The “next best” logic is based on site link costs where the lower cost is preferred.

Windows Server 2008 uses the SiteCostedReferrals behavior by default and does not require the Registry value to be set. Windows 2000 Server does not support this feature.

The SiteCostedReferrals Registry value should be defined across all domain controllers in a domain to ensure consistent behavior. The DFS service must be restarted or the domain controllers rebooted for the change to take effect.

This behavior is controlled via the following Registry value:

HKLM\System\CurrentControlSet\Services\Dfs\Parameters

Value: SiteCostedReferrals

Type: REG_DWORD

Data:

• Windows 2003

= Disabled

0 = Disabled

1 = Enabled

• Windows 2008

= Enabled
0 = Disabled
1 = Enabled

Automatic Site Coverage

For various reasons, it is possible that no domain controller exists for a particular domain at the local site.
To ensure that clients can locate a domain controller in the nearest available site, domain controllers attempt to register their DNS service location (SRV) resource records. These resource records pertain to sites that contain no domain controller for the domain of which they are a member. This functionality is commonly known as "automatic site coverage."

Automatic site coverage factors in the cost associated with the site links of a site without a domain controller. This cost helps determine which domain controller registers its SRV resource records for that site. The SRV resource records are registered by domain controllers from the site that has the lowest cost between its site link and the site that has no domain controller. This makes it possible for clients in the site without a domain controller to use the least expensive network connection to contact a domain controller in another site.

Source:
http://technet.microsoft.com/en-us/library/cc732322(WS.10).aspx
http://technet.microsoft.com/en-us/library/cc978016.aspx