Archive for August, 2012


In order for two sites to exchange replication data, they must be connected by a site link. A site link is a connection that enables replication traffic to travel between sites. Site links represent the physical connections available between sites.


Why to create Site Link?

When you create additional sites, you must select at least one site link for each site. Unless a site link is in place, connections cannot be made between computers at different sites, and replication between sites cannot take place. Additional site links are not created automatically; you must use Active Directory Sites and Services to create them.


Default Site Link

When you create the first domain in a forest, a default site link named DEFAULTIPSITELINK is also created. It includes the first site, and is located in the IP container in Active Directory. The site link can be renamed.


Site link attributes

When you create a site link, you must select the transport protocol it will use, give it a name, and add two or more sites to it. The sites are then connected. The characteristics of this connection are determined by the site link attributes, which can be configured. The connection characteristics are configured on the link, so all sites connected by a single site link will use the same replication path and transport. Configuring site link attributes is one part of configuring replication between sites. Site link attributes determine the characteristics of the connection in terms of the cost, frequency of replication traffic, and the protocols used.


Site link cost

Site link cost is a dimensionless number that represents the relative speed, reliability and preference of the underlying network. The lower the site link cost, the higher the priority for that link. For example, your organization has a site in Denver and a site in Paris with two connections between them: a high-speed connection and a dial-up connection in case the high-speed connection fails. You would configure two site links, one for each connection. Because the high-speed connection is preferable to a dial-up connection, you would configure the site link representing it with a lower cost than the site link for the dial-up line. Because the site link representing the high-speed connection has a lower cost, it has a higher priority, and that site link will always be used if possible. Setting site link cost enables you to determine the relative priority for each site link. The default cost value is 100, with possible values from one to 99999.


Site link replication Schedule

Replication schedule is another site link attribute that can be configured. When you configure the link’s schedule, you specify the times when the link is available for replication. Often, replication availability is configured for times when there is little other network traffic, for example from 1:00 A.M. to 4:00 A.M. The fewer hours a link is available for replication, the greater the latency between sites that are connected by that link. The need to have replication occur at off-peak hours should be balanced against the need for up-to-date information at each site connected by the link.


Site link replication frequency

When you configure the frequency of replication, you specify how many minutes Active Directory should wait before using the link to check for updates. The default value for replication frequency is 180 minutes, and the value you choose must fall between 15 minutes and one week. Replication frequency only applies to the times when the link is scheduled to be available. Longer intervals between replication cycles reduce network traffic and increase the latency between sites. Shorter intervals increase network traffic and decrease latency. The need to reduce network traffic should be balanced against the need for up-to-date information at each of the sites connected by the link.


Site link transport protocols

A transport protocol is a common language shared by computers to communicate during replication. Within a single site, there is only one protocol used for replication. When you create a site link, you must choose to use one of the following transport protocols:

1. Remote procedure call (RPC) over IP. RPC is an industry standard protocol for client/server communications, and provides reliable, high speed connectivity within sites. Between sites, RPC over IP enables replication of all Active Directory partitions. RPC over IP is the best transport protocol for replication between sites.

2. Simple mail transfer protocol (SMTP). SMTP supports intersite and interdomain replication of the schema, configuration, and global catalog. This protocol cannot be used for replication of the domain partition. This is because some domain operations, for example Group Policy, require the support of the File Replication service (FRS), which does not support an asynchronous transport for replication. If you use SMTP, you must install and configure a certificate authority to sign the SMTP messages and ensure the authenticity of directory updates. Additionally, SMTP does not provide the same level of data compression that RPC over IP enables.




Replication ensures that all information in Active Directory is current on all domain controllers and client computers across your entire network. Many networks consist of a number of smaller networks, and the network links between these networks may operate at varying speeds. Sites in Active Directory enable you to control replication traffic and other types of traffic related to Active Directory across these various network links. You can use subnet objects, site links, and site link bridges to help control the replication topology when configuring replication between sites. An efficient, reliable replication topology depends on the configuration of site links and site link bridges.


What Are Sites and Subnet Objects?



You use sites to control replication traffic, logon traffic, and requests to the Global Catalog server.



In Active Directory, sites help define the physical structure of a network. A site is defined by a set of Transmission Control Protocol/Internet Protocol (TCP/IP) subnet address ranges. Sites are used to define a group of domain controllers that are well-connected in terms of speed and cost. Sites consist of server objects, which contain connection objects that enable replication.


Subnet Objects

The TCP/IP subnet address ranges are represented by subnet objects that group computers. For example, a subnet object might represent all the computers on a floor in a building, or on a campus. Subnet objects are associated with sites and, because the subnet objects map to the physical network, so do the sites. For example, if you have three subnets that represent three campuses in a city, and these campuses are connected by high-speed, highly available connections, you could associate each of those subnets with the same site. A site can consist of one or more subnets. For example, on a network with three subnets in London and two in Boston, the administrator can create a site in London, a site in Boston, and then add the subnets to the respective sites.


Default Site

A default site is set up automatically when you install Windows Server on the first domain controller in a forest. This site is called Default-First-Site- Name. This site can be renamed. When you create your first domain in a forest it is automatically placed in the default site.


A global catalog server is a domain controller that stores two forest-wide partitions, schema and configuration, a read/write copy of the partition from its own domain, and also a partial replica of all other domain partitions in the forest. These partial replicas contain a read-only subset of the information in each domain partition.


How does replication affect the global catalog server?

When a new domain is added to a forest, the information about the new domain is stored in the configuration partition, which is replicated to all domain controllers, including global catalog servers, through normal forest-wide replication. Then each global catalog server becomes a partial replica of the new domain by contacting a domain controller for that domain and obtaining the partial replica information. The configuration partition also contains a list of all global catalog servers in the forest and provides this information to the domain controllers. Global catalog servers register special DNS records in the DNS zone that correspond to the Forest Root domain. These records, which are registered only in the Forest Root DNS zone, help clients and servers locate global catalog servers throughout the forest.


When you add domain controllers to a site, Active Directory uses the Knowledge Consistency Checker (KCC) to establish a replication path between domain controllers.


What is Knowledge Consistency Checker?

The KCC is a built-in process that runs on each domain controller and generates the replication topology for all directory partitions contained on that domain controller. The KCC runs at specified intervals (every 15 minutes by default) and designates replication routes between domain controllers that are the most favorable connections available at the time.


How KCC works?

To automatically generate a replication topology, the KCC evaluates information in the configuration partition on sites, the cost of sending data between these sites, any existing connection objects, and the replication protocols that can be used between the sites. Next, the KCC calculates the best connections for a domain controller’s directory partitions to other domain controllers. Additionally, if replication within a site becomes impossible or has a single point of failure, the KCC automatically establishes new connection objects between domain controllers to maintain Active Directory replication.



The Active Directory database is logically separated into directory partitions, a schema partition, a configuration partition, domain partitions, and application partitions. Each partition is a unit of replication, and each partition has its own replication topology. Replication is performed between directory partition replicas. All domain controllers in the same forest have at least two directory partitions in common: the schema and configuration partitions. All domain controllers in the same domain, in addition, share a common domain partition.


Schema Partition:

There is only one schema partition per forest. The schema partition is stored on all domain controllers in a forest. The schema partition contains definitions of all objects and attributes that can be created in the directory, and the rules for creating and manipulating them. Schema information is replicated to all domain controllers in the forest, so all objects must comply with the schema object and attribute definitions.


Configuration Partition:

There is only one configuration partition per forest. The configuration partition is stored on all domain controllers in a forest. The configuration partition contains information about the forest-wide Active Directory structure, including what domains and sites exist, which domain controllers exist in each, and which services are available. Configuration information is replicated to all domain controllers in a forest.


Domain Partition:

There can be many domain partitions per forest. The domain partitions are stored on all of the domain controllers of the given domain. A domain partition holds information about all domain-specific objects created in that domain, including users, groups, computers, and organizational units. The domain partition is replicated to all domain controllers of that domain. All objects in every domain partition in a forest are stored in the Global Catalog with only a subset of its attribute values.



The replication process occurs between two domain controllers at a time. Over time, replication synchronizes information in Active Directory for an entire forest of domain controllers. To create a replication topology, Active Directory must determine which domain controllers replicate data with other domain controllers.


This is how the name resolution works:

  1. You try to open up a Webpage on the Ignited Soul website, to do so, you type in the address bar of your browser and then press Enter, That’s when the Name Resolution begins.
  2. Your Computer sends out a request to its local DNS server or at least to one of the servers listed in its IP configuration settings for the same.
  3. If this server doesn’t include the name in its own database or cache, it sends a referral request to the name server. Because the Ignitedsoul site name ends in .com, the DNS server sends the referral to the .com name server.
  4. The .com name server is the authority for all names that end in the .com suffix. This server knows the location of all DNS servers that are the final authorities for a particular name ending with .com. in this case; it sends the request to the authoritative DNS server for the name.
  5. The DNS server for sends the corresponding IP address for the requested page to the client computer.
  6. The name resolver on the client uses the IP address to request the actual page from its internet provider.
  7. If the page is not already in the local cache of the internet provider, it requests the actual page and sends it to the client.

This DNS Name resolution process occurs within seconds, and the website appears almost as fast as you type it in browser, also depending on the speed of your Internet connection and the current load of the requested server. That’s what happens when you look at the green progress bar at the bottom of your browser. The actual progress also includes downloading the content such as the text and the graphics to your own computer.

There are around 5 types of routers:

– Wired Router: These are devices that connect directly to computers using cable. One of the ports on the Wired Router allows the router to connect to a modem for receiving internet, while the other set of ports transmits the data to computers using the network cable.

– Wireless Router: This is almost same as the wired router, this device connects to the Modem using wire, but while transmitting the data it can do it in two types, the Wired and Wireless. This device converts the data packets to radio signals.

– Core Routers: A core router is a wired or wireless router that distributes Internet data packets within a network, but does not distribute data packets between multiple networks.

– Edge Routers: an edge router is a wired or wireless router that distributes Internet data packets between one or more networks, but does not distribute data packets within a network.

– Virtual Router: Unlike a physical wired or wireless router, a virtual router acts as a default router for computers sharing a network. The router functions using the Virtual Router Redundancy Protocol (VRRP), which becomes active when a primary, physical router fails or otherwise becomes disabled.

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and routing Internet Protocol packets. It is a way to allocate and specify the Internet addresses used in inter-domain routing more flexibly than with the original system of Internet Protocol (IP) address classes. As a result, the number of available Internet addresses has been greatly increased. CIDR is now the routing system used by virtually all gateway hosts on the Internet’s backbone network.

IP addresses are described as consisting of two groups of bits in the address: the more significant part is the network address, which identifies a whole network or subnet, and the less significant portion is the host identifier, which specifies a particular interface of a host on that network. This division is used as the basis of traffic routing between IP networks and for address allocation policies. Classful network design for IPv4 sized the network address as one or more 8-bit groups, resulting in the blocks of Class A, B, or C addresses. Classless Inter-Domain Routing allocates address space to Internet service providers and end users on any address bit boundary, instead of on 8-bit segments. In IPv6, however, the interface identifier has a fixed size of 64 bits by convention, and smaller subnets are never allocated to end users.

CIDR notation is a syntax of specifying IP addresses and their associated routing prefix. It appends to the address a slash character and the decimal number of leading bits of the routing prefix, e.g., for IPv4, and 2001:db8::/32 for IPv6.