Archive for the ‘DNS’ Category

Record type

Name

Description

A Address Record Maps a hostname to an IP address
PTR Pointer Record Maps an IP address to a hostname
CNAME Alias Record Maps an alias to a hostname
MX Mail Exchanger Record Specifies a mail route for a domain
NS Name Server Record Specifies name servers for a given domain
SOA Start of Authority Record Contains administrative data about a zone, including the primary name server
SRV Service Record Maps a particular service (e.g., LDAP) to one or more hostnames

One important resource record to note is the SRV record type. SRV records are used extensively by domain controllers and Active Directory clients to locate servers that have a particular service.

 

By Default a Global Catalog is created automatically on the initial Domain Controller in the forest. It stores a full replica of all the objects in the directory for its host domain and a partial replica of all objects contained in the directory of every other domain in the forest. The replica is partial because it stores some, but not all, of the property values for every object in the forest.

The Global Catalog performs two key directory roles:

–  It enables network logon by providing universal group membership information to a domain controller when a logon process is initiated.

–  It enables finding directory information in the entire forest regardless of which domain in the forest actually contains the data.

When a user logs in to the network, the global catalog provides universal group membership information for the account sending the logon request to the domain controller. If there is only one domain controller in the Domain, the domain controller and the global catalog are the same server. If there are multiple domain controllers in the network, the global catalog is hosted on the domain controller configured as such. If a Global Catalog is not available when a user initiates a network logon process, the user is only able to log on to the local computer.

Note: If a user is a member of the Domain Admins group, then they will be able to log on to the network even when the Global Catalog is not available.

The Global Catalog is designed to respond to queries about objects anywhere in the forest with maximum speed and minimum network traffic, because a single Global Catalog contains information about objects in all domain in the forest, a query about an object can be resolved by a global catalog in the domain in which the query is initiated. Thus finding the information in the directory does not produce unnecessary query traffic across domain boundaries.

You can optionally configure any domain controller to host a global catalog, based on your Company’s requirements for servicing logon requests and search queries.

After Additional domain controllers are installed in the domain, you can change the default location of the global catalog to another domain controller using the Active Directory Sites and Services.

 

Introduction

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.

 

Introduction

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.

Introduction

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.

Partitions:-

Introductions

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.

 

REPLICATIONS:

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.