The Role of Domain Controllers

8/3/2019 The Role of Domain Controllers

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The Role of Domain Controllers

A domain controller holds a replica of the Active Directory directory for the domain to which it belongs.

It is also responsible for managing that directory.

The domain controller is responsible for replicating all changes made to their

Active Directory replica to the remainder of the domain controllers within the

domain.

Domain controllers also manage access to network resources in the

domain. They locate Active Directory objects, authenticate access to these objects,

validate user logon attempts, and authenticate user passwords

Domain controllers track user account information through Security Identifiers

(SIDs). a user attempts to log on to the system, a request to authenticate the useris sent to each domain controller within the domain.

Multiple domain controllers provide fault tolerance in your Active Directory

environment. In the Windows NT domain model, no changes could be made to the

domain database when the primary domain controller was unavailable.

Domain controllers also integrate with network services such as DNS, DHCP,

Kerberos security, and Remote Access. This in turn facilitates centralized

management and security.

Considerations for Multiple Domain Controllers

The number of domain controllers which are needed within your domain are determined by the

following factors:

The number of users in the domain

The number of computers in the domain

The application requirements in the domain

The level of fault tolerance required for the domain - at least two domain controllersshould exist in the domain.
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How to create the first domain controller

Use the steps below to create a domain controller

1. Log on to the member server that you want to configure as a domain controller

2. Click Start, click Run, and enter dcpromo in the Run dialog box. Click OK.

3. This action starts the Active Directory Installation Wizard.

4. On the initial Welcome page of the wizard, click next.

5. On the Operating System Compatibility page, click Next.

6. On the Domain Controller Type page, you are prompted to choose one of the options listed

below. Click Next after you have selected the appropriate option.

7. The options available on the Create New Domain Page are listed below. Once you have

made the appropriate selection, click Next

8. On the New Domain Name page, you have to enter the fully qualified domain name(FQDN) of the new domain. Click Next

9. On the NetBIOS Domain Name page, you have to verify whether the default NetBIOS

domain name should be used. You can accept the default name by clicking Next.

10. On the Database and Log Folders page, you have to specify a location for the Active

Directory database, and specify a location for the Active Directory log files. The locations that

you specify should preferably exist on an NTFS volume. Click Next.

11. On the Shared System Volume page, you need to specify the location of the SYSVOL

folder. This folder has to be located on a NTFS volume. Click Next.

12.On the DNS Registration Diagnostics page, you can choose one of the following options:

13. On the Permissions page, you have to choose the default permissions for user and group

objects.

14. On the Directory Services Restore Mode Administrator Password page, you have to enter

the appropriate password in the two password text boxes.

15. The Summary page lists all the configuration settings that you have specified while

navigating through the various pages of the Active Directory Installation Wizard. Once you

have verified that the correct settings have been specified, click Next

16.At this stage, the Active Directory Installation Wizard installs Active Directory.

17. On the Completing the Active Directory Installation Wizard page, click Finish. If this is the

first domain controller, it is placed in the Default-First-Site-Name default site.


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Backing up Domain Controllers

1. Log on to the domain

2. Click Start, All Programs, Accessories, System Tools, and then click Backup.

3.When the Welcome To The Backup Or Restore Wizard page opens, click Next.

4. In the Backup Or Restore page, choose the Backup Files And Settings option. Click Next.

5. When the What To Back Up page opens, choose the Let Me Choose What To Back Up

option. Click Next.

6. In the Items To Back Up page, select System State. Click Next.

7. When the Backup Type, Destination, And Name page opens, choose the appropriate option

in the Select The Backup Type box.

8. Choose the location for the backup in the Choose A Place To Save Your Backup box.

9. Enter a name for the backup job in the Type A Name For This Backup box. Click Next.

10. Click the Advanced button on the Completing The Backup Or Restore Wizard page.

11. When the Type Of Backup page opens, choose the Normal option for the backup type.

Click Next.

12. In the How To Back Up page, it is recommended to select the Verify Data After Backup

option.

13. If hardware compression is supported, and you are using a tape mechanism, click the Use

Hardware Compression, If Available option. Click Next.

14. When the Backup Options page opens, choose Replace The Existing Backups, and choose

Allow Only The Owner And The Administrator Access To The Backup Data And To Any Backups

Appended To This Medium. Click Next.

15. Select the Now option in the When To Back Up page. Click Next.

16. Click Finish

17. Click the Report button on the Backup Progress page to view a report on the backup job

just completed

Restoring Domain Controllers

When you restore system state data, including Active Directory to a domain controller, you basically

have to decide on the method of restore to perform. System state data can be restored on the domain

controller by one of the following methods:

Nonauthoritative restore: When a nonauthoritative restore is performed, Active

Directory is restored from backup media on the domain controller. This information is then

updated during replication from the other domain controllers. The nonauthoritative restore

method is the default method to restore system state data to a domain controller

Authoritative restore: In an authoritative restore, Active Directory is installed to the

point of the last backup job. This method is typically used to recover Active Directory objects

that were deleted in error. An authoritative restore is performed by first performing a

nonauthoritative restore, and then running the Ntdsutil utility prior to restarting the server.

You use the Ntdsutil utility to indicate those items that are authoritative. Items that are

marked as authoritative are not updated when the other domain controllers replicate to the


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particular domain controller. Instead, these items are replicated to the other domain

controllers.

How to restore system state data on a domain controller nonauthoritativerestore

1. Restart the local computer

2. During startup, press F8 to access the Windows Advanced Options.

3. Proceed to choose Directory Services Restore Mode. Press Enter

4. Choose the operating system that should be started at the Please Select The Operating

System To Start prompt. Press Enter

5. Log on to the domain using an account with Administrator privileges.

6. Click OK when a message appears stating that Windows is running in safe mode.

7. Click Start, All Programs, Accessories, System Tools, and then click Backup.

8. When the Welcome To The Backup Or Restore Wizard page opens, click Next.

9. In the Backup Or Restore page, choose the Restore Files And Settings option. Click Next.

10. On the What To Restore page, choose the data that should be restored. Click Next.

11. Verify that the media that contains the backup file is in the proper place.

12. Click Finish to start the nonauthoritative restore.

13. Click OK when a message appears stating that the restore will overwrite existing system

state data.

14. When the restore process completes, restart the computer.

How to restore system state data on a domain controller authoritative

restore method

1. You first have to perform a nonauthoritative restore of the system state data to the

domain controller. This restore method was outlined in the preceding section.

2. Proceed to restart the computer.

3. During startup, press F8 to access the Windows Advanced Options.

4. Proceed to choose Directory Services Restore Mode. Press Enter

5. Choose the operating system that should be started at the Please Select The Operating

System To Start prompt. Press Enter

6. Log on to the domain using an account with Administrator privileges.

7. Click OK when a message appears stating that Windows is running in safe mode.

8. Click Start, and then Command Prompt.

9. Enter and run Ntdsutil.

10. From the Ntdsutil: prompt, insert the following: authoritative restore. Press Enter

11. The authoritative restore: prompt opens next. This is where you specify what you want to

restore through its distinguished name. For example, if you want to restore an object, enter

restore object. To restore the Active Directory database, enter restore database.

12. Push Enter for the authoritative restore to start.

13. Enter quit to exit out of Ntdsutil.

14. Restart the domain controller and reconnect it to the network.


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15.All changes from the other domain controllers that were not marked as authoritative are

replicated to this particular domain controller. The changes that are marked as authoritative

are replicated from this particular domain controller to the remainder of the domain

controllers.

What is DHCP?

The DHCP is engaged in assigning unique dynamic IP addresses and the corresponding subnet

masks and default gateways to TCP/IP running computers within a particularserver network.

How does the DHCP work?In a network, a DHCP server manages a pool of IP addresses, as well as default gateway details,

DNS details and other information for the clients network configuration.

When a new computer is introduced into a DHCP server-enabled network, it will send a query to

the DHCP server requesting all the necessary information. When the query reaches the DHCP

server, it will grant the new computer a new IP address and a lease - a time frame for which the

computer can use this IP address, as well as other configuration details. The whole process takes

place immediately after the new computer boots, and to be successful, it has to be completed

before initiating IP based communication with other hosts in the network.

DHCP allocation methodsDepending on its configuration, the DHCP server can work in 3 ways:

Dynamic allocationWhen the DHCP server is configured to use dynamic allocation, this means that it uses a lease

policy. This way, when an assigned IP address from the available pool is no longer used, it will be

transferred back to the pool, making it available for someone else to use

Automatic allocationAs soon as a client connects, the DHCP server provides him with an IP address from the IP address

pool. However, when automatic allocation is used, the DHCP server keeps a database of previous

IP grants, and tries to give the client the same IP address he used the last time, if available.

Static allocation

. With the static allocation, the DHCP sever keeps a database with all clients' LAN MAC addressesand gives them an IP address only if their MAC address is in the database.
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What is DNS?translates the name into its corresponding IP address (e.g. the domain name NTC Hosting.com is

translated to 66.40.65.49). Thanks to the DNS, we do not need to bother to remember

complicated numeric combinations to reach a certain website - we can use its meaningful and

much easier to remember domain name instead.

Conditional forwarders

Conditional forwarders are DNS servers that only forward queries for specific domainnames. Instead of forwarding allqueries it cannot resolve locally to a forwarder, a

conditional forwarder is configured to forward a query to specific forwarders based on thedomain name contained in the query. Forwarding according to domain names improves

conventional forwarding by adding a name-based condition to the forwarding process.

The conditional forwarder setting for a DNS server consists of the following:

The domain names for which the DNS server will forward queries.

One or more DNS server IP addresses for each domain name specified.

RADIUSRemote Authentication Dial In User Service (RADIUS) is a networking protocolthat provides

centralized Authentication, Authorization, and Accounting (AAA) management for computers to connect

and use a network service

RADIUS ROLES:

1. to authenticate users or devices before granting them access to a network,

2. to authorize those users or devices for certain network services and

3. to account for usage of those services.
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RAID

RAID (an acronym forredundant array of independent disks; originally redundant array of

inexpensive disks) is a storage technology that combines multipledisk drivecomponents into a logical

unit. Data is distributed across the drives in one of several ways called "RAID levels", depending on what

level ofredundancyand performance (via parallel communication) is required.

RAID is now used as an umbrella termforcomputer data storageschemes that can divide and

replicatedata among multiple physical drives. The physical drives are said to be in a RAID,[5]which is

accessed by the operating systemas one single drive. The different schemes or architectures are named

by the word RAID followed by a number (e.g., RAID 0, RAID 1). Each scheme provides a different

balance between two key goals: increase data reliabilityand increase input/outputperformance.

RAID PROBLEMS

10.1 Correlated failures

10.2 Atomicity

10.3 Write cache reliability

10.4 Equipment compatibility

10.5 Data recovery in the event of a failed array

10.6 Drive error recovery algorithms

10.7 Recovery time is increasing
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10.8 Operator skills, correct operation

Internet Information Services (IIS)

Internet Information Services (IIS) formerly called Internet Information Server is a web

serverapplication and set of feature extension modules created byMicrosoft for use withMicrosoft

Windows. IIS 7.5 supports HTTP,HTTPS,FTP,FTPS,SMTP and NNTP. It is an integral part ofWindows

Serverfamily of products, as well as certain editions ofWindows XP,Windows Vista and Windows 7. IIS is

not turned on by default when Windows is installed.

Features

The architecture of IIS 7 is modular. Modules, also called extensions, can be added or removed

individually so that only modules required for specific functionality have to be installed. IIS 7 includes

native modules as part of the full installation. These modules are individual features that the server uses

to process requests and include the following:[23]

HTTP modules Used to perform tasks specific to HTTP in the request-processing pipeline, such as

responding to information and inquiries sent in client headers, returning HTTP errors, and redirecting

requests.

Security modules Used to perform tasks related to security in the request-processing pipeline, such as

specifying authentication schemes, performing URL authorization, and filtering requests.

Content modules Used to perform tasks related to content in the request-processing pipeline, such as

processing requests for static files, returning a default page when a client does not specify a resource in a

request, and listing the contents of a directory.
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Compression modules Used to perform tasks related to compression in the request-processing pipeline,

such as compressing responses, applying Gzip compression transfer coding to responses, and

performing pre-compression of static content.

Caching modules Used to perform tasks related to caching in the request-processing pipeline, such as

storing processed information in memory on the server and using cached content in subsequent requestsfor the same resource.

Logging and Diagnostics modules Used to perform tasks related to logging and diagnostics in the

request-processing pipeline, such as passing information and processing status to HTTP.sys for logging,

reporting events, and tracking requests currently executing in worker processes.

IIS 6.0 and higher support the following authenticationmechanisms:[24]

Anonymous authentication

Basic access authentication

Digest access authentication Integrated Windows Authentication

UNC authentication

.NET Passport Authentication (Removed in Windows Server 2008 and IIS 7.0)[25]

Certificate authentication

IIS 7.5 includes the following additional or enhanced security features:[26]

Client Certificate Mapping

IP Security

Request Filtering

URL Authorization

Authentication changed slightly between IIS 6.0 and IIS 7, most notably in that the anonymous user which

was named "IUSR_{machinename}" is a built-in account in Vista and future operating systems and

named "IUSR". Notably, in IIS 7, each authentication mechanism is isolated into its own module and can

be installed or uninstalled.[25]

Microsoft Cluster Server

Microsoft Cluster Server(MSCS) is software designed to allow servers to work together as acomputer

cluster, to provide failover and increased availability of applications, orparallelcalculating power in case

ofhigh-performance computing (HPC)clusters (as insupercomputing)
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Microsoft has three technologies for clustering: Microsoft Cluster Service (MSCS), Component Load

Balancing (CLB) (part of Application Center 2000), and Network Load Balancing Services(NLB).

In Windows Server 2008 and Windows Server 2008 R2 the MSCS service has been renamed

to Windows Server Failover Clusteringand the Component Load Balancing (CLB) feature has been

deprecated.

Server clusters overview

A server cluster is a group of independent computer systems, known as nodes, workingtogether as a single system to ensure that critical applications and resources remainavailable to clients. These nodes must be running Microsoft Windows Server 2003,Enterprise Edition or Microsoft Windows Server 2003, Datacenter Edition. Clusteringallows users and administrators to access and manage the nodes as a single system ratherthan as separate computers. For more information about nodes, see Nodes.

A server cluster can consist of up to eight nodes and may be configured in one of threeways: as a single node server cluster, as a single quorum device server cluster, or as amajority node set server cluster. For more information about these three server clustermodels, see Choosing a Cluster Model.

Every node may be attached to one or more cluster storage devices. For most versions ofWindows Server 2003, Enterprise Edition or Windows Server 2003, Datacenter Edition, thechoices for cluster storage include iSCSI, Serial Attached SCSI, parallel SCSI, and FibreChannel. The following table provides details about the storage you can use with eachversion of the operating system, along with the maximum number of nodes you can havewith each storage type:

Cluster application types

Applications that run in a server cluster fall into one of four categories:

Cluster-unaware applications

These types of applications do not interact with the server cluster at all but can still fail over. Failure

detection is limited. The Cluster service protects these applications mainly against hardware

failures.

Cluster-aware applications

These types of applications are characterized by superior failure detection. The Cluster service can

protect these applications not only against hardware but also against software failures.

Cluster management applications

These types of applications, which include Cluster Administrator and Cluster.exe, allow

administrators to manage and configure clusters. For more information, seeServer Cluster

Components.

Custom resource types

Resource types provide customized cluster management and instrumentation for applications,

services, and devices. For more information, seeResource types.
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Simple Mail Transfer Protocol (SMTP)

Simple Mail Transfer Protocol (SMTP) is an Internet standard forelectronic mail (e-mail) transmission

across Internet Protocol (IP) networks. SMTP was first defined by RFC 821 (1982, eventually

declared STD10),[1] and last updated byRFC 5321 (2008)[2]which includes theextended SMTP(ESMTP)

additions, and is the protocol in widespread use today. SMTP is specified for outgoing mail transport anduses TCPport 25. The protocol for new submissions is effectively the same as SMTP, but it uses port 587

instead. SMTP connections secured by SSL are known by the shorthand SMTPS, though SMTPS is not a

protocol in its own right.

While electronicmail serversand othermail transfer agents use SMTP to send and receive mail

messages, user-level client mail applications typically only use SMTP for sending messages to a mail

server forrelaying. For receiving messages, client applications usually use either the Post Office

Protocol (POP) or theInternet Message Access Protocol (IMAP) or a proprietary system (such as

Microsoft Exchange orLotus Notes/Domino) to access their mail box accounts on a mail server.

The Hypertext Transfer Protocol (HTTP)

The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative,

hypermedia information systems.[1] HTTP is the foundation of data communication for theWorld Wide

Web.

The standards development of HTTP was coordinated by the Internet Engineering Task Force (IETF) and

the World Wide Web Consortium (W3C), culminating in the publication of a series ofRequests for

Comments(RFCs), most notablyRFC 2616 (June 1999), which defines HTTP/1.1, the version of HTTP in

common use.

HTTP session

An HTTP session is a sequence of network request-response transactions. An HTTP client initiates a

request by establishing aTransmission Control Protocol(TCP) connection to a particularporton a server(typically port 80; see List of TCP and UDP port numbers). An HTTP server listening on that port waits for

a client's request message. Upon receiving the request, the server sends back a status line, such as

"HTTP/1.1 200 OK", and a message of its own, the body of which is perhaps the requested resource, an

error message, or some other information.[1]

Request message
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The request message consists of the following:

A request line, such as GET /images/logo.png HTTP/1.1, which requests a resource

called /images/logo.png from the server.

Headers, such as Accept-Language: en

An empty line.

An optional message body.

Simple Network Management Protocol (SNMP)

Simple Network Management Protocol (SNMP) is an "Internet-standard protocol for managing devices

on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations,printers, modem racks, and more."[1]It is used mostly in network management

systems tomonitornetwork-attached devices for conditions that warrant administrative attention. SNMP is

a component of theInternet Protocol Suiteas defined by the Internet Engineering Task Force (IETF). It

consists of a set ofstandardsfor network management, including anapplication layerprotocol, a

database schema, and a set ofdata objects.[2]

SNMP exposes management data in the form of variables on the managed systems, which describe the

system configuration. These variables can then be queried (and sometimes set) by managing

applications.

An SNMP-managed network consists of three key components:

Managed device

Agent software which runs on managed devices

Network management system (NMS) software which runs on the manager

Protocol details

SNMP operates in theApplication Layerof the Internet Protocol Suite (Layer 7of the OSI model). The

SNMP agent receives requests on UDP port 161. The manager may send requests from any available

source port to port 161 in the agent. The agent response will be sent back to the source port on the

manager. The manager receives notifications (Traps andInformRequests) on port 162. The agent may
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generate notifications from any available port. When used withTransport Layer Security orDatagram

Transport Layer Securityrequests are received on port 10161 and traps are sent to port 10162.[3].

SNMPv1 specifies five coreprotocol data units(PDUs). Two other

PDUs, GetBulkRequestand InformRequestwere added in SNMPv2 and carried over to SNMPv3.

All SNMP PDUs are constructed as follows:

IP

headerUDP header version community PDU-type request-id error-status error-index variable bindings

Routing

Routing is the process of selecting paths in a network along which to send network traffic. Routing is

performed for many kinds of networks, including the telephone network(Circuit switching), electronic data

networks (such as the Internet), and transportation networks. This article is concerned primarily with

routing in electronic data networks using packet switchingtechnology.

In packet switching networks, routing directspacket forwarding, the transit of logically addressed packets

from their source toward their ultimate destination through intermediate nodes, typically hardware devices

called routers, bridges,gateways,firewalls, orswitches. General-purpose computers can also forward

packets and perform routing, though they are not specialized hardware and may suffer from limited

performance. The routing process usually directs forwarding on the basis ofrouting tableswhich maintain

a record of the routes to various network destinations. Thus, constructing routing tables, which are held inthe router'smemory, is very important for efficient routing. Most routing algorithms use only one network

path at a time, but multipath routing techniques enable the use of multiple alternative paths.

Routing, in a more narrow sense of the term, is often contrasted withbridgingin its assumption

thatnetwork addressesare structured and that similar addresses imply proximity within the network.

Because structured addresses allow a single routing table entry to represent the route to a group of

devices, structured addressing (routing, in the narrow sense) outperforms unstructured addressing
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(bridging) in large networks, and has become the dominant form of addressing on the Internet, though

bridging is still widely used within localized environments.

Topology distribution

In a practice known as static routing (or non-adaptive routing), small networks may use manually

configured routing tables. Larger networks have complextopologies that can change rapidly, making the

manual construction of routing tables unfeasible. Nevertheless, most of thepublic switched telephone

network(PSTN) uses pre-computed routing tables, with fallback routes if the most direct route becomes

blocked (seerouting in the PSTN). Adaptive routing, or dynamic routing, attempts to solve this problem by

constructing routing tables automatically, based on information carried by routing protocols, and allowing

the network to act nearly autonomously in avoiding network failures and blockages.

Examples of adaptive-routing algorithms are the Routing Information Protocol (RIP) and the Open-

Shortest-Path-First protocol (OSPF). Adaptive routing dominates the Internet. However, the configuration

of the routing protocols often requires a skilled touch; networking technology has not developed to the

point of the complete automation of routing.[citation needed]

[edit]Distance vector algorithms

Main article: Distance-vector routing protocol

Distance vector algorithms use the Bellman-Fordalgorithm. This approach assigns a number, the cost, to

each of the links between each node in the network. Nodes will send information from point A to point B

via the path that results in the lowest total cost(i.e. the sum of the costs of the links between the nodes

used).

The algorithm operates in a very simple manner. When a node first starts, it only knows of its immediate

neighbours, and the direct cost involved in reaching them. (This information, the list of destinations, the

total cost to each, and the next hop to send data to get there, makes up the routing table, ordistance

table.) Each node, on a regular basis, sends to each neighbour its own current idea of the total cost to get

to all the destinations it knows of. The neighbouring node(s) examine this information, and compare it to

what they already 'know'; anything which represents an improvement on what they already have, they

insert in their own routing table(s). Over time, all the nodes in the network will discover the best next hop

for all destinations, and the best total cost.

When one of the nodes involved goes down, those nodes which used it as their next hop for certain

destinations discard those entries, and create new routing-table information. They then pass this

information to all adjacent nodes, which then repeat the process. Eventually all the nodes in the network

receive the updated information, and will then discover new paths to all the destinations which they can

still "reach".

[edit]Link-state algorithms

Main article: Link-state routing protocol

When applying link-state algorithms, each node uses as its fundamental data a map of the network in the

form of a graph. To produce this, each node floods the entire network with information about what other

nodes it can connect to, and each node then independently assembles this information into a map. Using
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this map, each router then independently determines the least-cost path from itself to every other node

using a standard shortest pathsalgorithm such asDijkstra's algorithm. The result is a tree rooted at the

current node such that the path through the tree from the root to any other node is the least-cost path to

that node. This tree then serves to construct the routing table, which specifies the best next hop to get

from the current node to any other node.

[edit]Optimised Link State Routing algorithm

Main article: Optimized Link State Routing Protocol

A link-state routing algorithm optimised formobile ad-hoc networks is the Optimised Link State Routing

Protocol (OLSR).[1] OLSR is proactive; it uses Hello and Topology Control (TC) messages to discover and

disseminate link state information through the mobile ad-hoc network. Using Hello messages, each node

discovers 2-hop neighbor information and elects a set ofmultipoint relays(MPRs). MPRs distinguish

OLSR from other link state routing protocols.

[edit]Path vector protocol

Main article: Path vector protocol

Distance vector and link state routing are both intra-domain routing protocols. They are used inside

an autonomous system, but not between autonomous systems. Both of these routing protocols become

intractable in large networks and cannot be used inInter-domain routing. Distance vector routing is

subject to instability if there are more than a few hops in the domain. Link state routing needs huge

amount of resources to calculate routing tables. It also creates heavy traffic because of flooding.

Path vector routing is used for inter-domain routing. It is similar to distance vector routing. In path vector

routing we assume there is one node (there can be many) in each autonomous system which acts on

behalf of the entire autonomous system. This node is called the speaker node. The speaker node creates

a routing table and advertises it to neighboring speaker nodes in neighboring autonomous systems. The

idea is the same as distance vector routing except that only speaker nodes in each autonomous systemcan communicate with each other. The speaker node advertises the path, not the metric of the nodes, in

its autonomous system or other autonomous systems. Path vector routing is discussed in RFC 1322; the

path vector routing algorithm is somewhat similar to the distance vector algorithm in the sense that each

border router advertises the destinations it can reach to its neighboring router. However, instead of

advertising networks in terms of a destination and the distance to that destination, networks are

advertised as destination addresses and path descriptions to reach those destinations. A route is defined

as a pairing between a destination and the attributes of the path to that destination, thus the name, path

vector routing, where the routers receive a vector that contains paths to a set of destinations. The path,

expressed in terms of the domains (or confederations) traversed so far, is carried in a special path

attribute that records the sequence of routing domains through which the reachability information has

passed.

[edit]Comparison of routing algorithms

Distance-vector routing protocols are simple and efficient in small networks and require little, if any,

management. However, traditional distance-vector algorithms have poorconvergenceproperties due to

the count-to-infinity problem.
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This has led to the development of more complex but more scalable algorithms for use in large networks.

Interior routing mostly uses link-state routing protocolssuch asOSPF and IS-IS.

A more recent development is that of loop-freedistance-vector protocols (e.g., EIGRP). Loop-free

distance-vector protocols are as robust and manageable as naive distance-vector protocols, but avoid

counting to infinity, and have good worst-caseconvergence times.

[edit]Path selection

Path selection involves applying a routing metricto multiple routes, in order to select (or predict) the best

route.

In the case of computer networking, the metric is computed by a routing algorithm, and can cover such

information asbandwidth,network delay,hop count, path cost, load, MTU, reliability, and communication

cost (see e.g. this survey for a list of proposed routing metrics). The routing table stores only the best

possible routes, whilelink-stateor topological databases may store all other information as well.

Because a routing metric is specific to a given routing protocol, multi-protocol routers must use some

external heuristic in order to select between routes learned from different routing protocols.Cisco'srouters, for example, attribute a value known as the administrative distance to each route, where smaller

administrative distances indicate routes learned from a supposedly more reliable protocol.

A local network administrator, in special cases, can set up host-specific routes to a particular machine

which provides more control over network usage, permits testing and better overall security. This can

come in handy when required to debug network connections or routing tables.

[edit]Multiple agents

In some networks, routing is complicated by the fact that no single entity is responsible for selecting

paths: instead, multiple entities are involved in selecting paths or even parts of a single path.

Complications or inefficiency can result if these entities choose paths to optimize their own objectives,which may conflict with the objectives of other participants.

A classic example involves traffic in a road system, in which each driver picks a path which minimizes

their own travel time. With such routing, theequilibrium routes can be longer than optimal for all drivers. In

particular, Braess paradox shows that adding a new road can lengthen travel times for all drivers.

In another model, for example used for routing automated guided vehicles (AGVs) on a terminal,

reservations are made for each vehicle to prevent simultaneous use of the same part of an infrastructure.

This approach is also referred to as context-aware routing.[2]

The Internet is partitioned into autonomous systems(ASs) such asinternet service providers (ISPs), each

of which has control over routes involving its network, at multiple levels. First, AS-level paths are selected

via the BGPprotocol, which produces a sequence of ASs through which packets will flow. Each AS may

have multiple paths, offered by neighboring ASs, from which to choose. Its decision often involves

business relationships with these neighboring ASs,[3]which may be unrelated to path quality or latency.

Second, once an AS-level path has been selected, there are often multiple corresponding router-level

paths, in part because two ISPs may be connected in multiple locations. In choosing the single router-

level path, it is common practice for each ISP to employ hot-potato routing: sending traffic along the path
http://en.wikipedia.org/wiki/Link-state_routing_protocolhttp://en.wikipedia.org/wiki/Link-state_routing_protocolhttp://en.wikipedia.org/wiki/OSPFhttp://en.wikipedia.org/wiki/OSPFhttp://en.wikipedia.org/wiki/IS-IShttp://en.wikipedia.org/wiki/IS-IShttp://en.wikipedia.org/wiki/Distance-vector_protocolshttp://en.wikipedia.org/wiki/Distance-vector_protocolshttp://en.wikipedia.org/wiki/EIGRPhttp://en.wikipedia.org/wiki/Convergence_(routing)#Convergence_timehttp://en.wikipedia.org/wiki/Convergence_(routing)#Convergence_timehttp://en.wikipedia.org/wiki/Convergence_(routing)#Convergence_timehttp://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=8http://en.wikipedia.org/wiki/Metrics_(networking)http://en.wikipedia.org/wiki/Metrics_(networking)http://en.wikipedia.org/wiki/Bandwidth_(computing)http://en.wikipedia.org/wiki/Bandwidth_(computing)http://en.wikipedia.org/wiki/Bandwidth_(computing)http://en.wikipedia.org/wiki/Network_delayhttp://en.wikipedia.org/wiki/Network_delayhttp://en.wikipedia.org/wiki/Hop_counthttp://en.wikipedia.org/wiki/MTU_(networking)http://rainer.baumann.info/public/tik262.pdfhttp://en.wikipedia.org/wiki/Link-statehttp://en.wikipedia.org/wiki/Link-statehttp://en.wikipedia.org/wiki/Link-statehttp://en.wikipedia.org/wiki/Ciscohttp://en.wikipedia.org/wiki/Ciscohttp://en.wikipedia.org/wiki/Ciscohttp://en.wikipedia.org/wiki/Administrative_distancehttp://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=9http://en.wikipedia.org/wiki/Nash_equilibriumhttp://en.wikipedia.org/wiki/Nash_equilibriumhttp://en.wikipedia.org/wiki/Braess_paradoxhttp://en.wikipedia.org/wiki/Automated_guided_vehiclehttp://en.wikipedia.org/wiki/Routing#cite_note-1http://en.wikipedia.org/wiki/Routing#cite_note-1http://en.wikipedia.org/wiki/Autonomous_system_(Internet)http://en.wikipedia.org/wiki/Autonomous_system_(Internet)http://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Border_Gateway_Protocolhttp://en.wikipedia.org/wiki/Border_Gateway_Protocolhttp://en.wikipedia.org/wiki/Routing#cite_note-2http://en.wikipedia.org/wiki/Routing#cite_note-2http://en.wikipedia.org/wiki/Hot-potato_routinghttp://en.wikipedia.org/wiki/Hot-potato_routinghttp://en.wikipedia.org/wiki/Link-state_routing_protocolhttp://en.wikipedia.org/wiki/OSPFhttp://en.wikipedia.org/wiki/IS-IShttp://en.wikipedia.org/wiki/Distance-vector_protocolshttp://en.wikipedia.org/wiki/EIGRPhttp://en.wikipedia.org/wiki/Convergence_(routing)#Convergence_timehttp://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=8http://en.wikipedia.org/wiki/Metrics_(networking)http://en.wikipedia.org/wiki/Bandwidth_(computing)http://en.wikipedia.org/wiki/Network_delayhttp://en.wikipedia.org/wiki/Hop_counthttp://en.wikipedia.org/wiki/MTU_(networking)http://rainer.baumann.info/public/tik262.pdfhttp://en.wikipedia.org/wiki/Link-statehttp://en.wikipedia.org/wiki/Ciscohttp://en.wikipedia.org/wiki/Administrative_distancehttp://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=9http://en.wikipedia.org/wiki/Nash_equilibriumhttp://en.wikipedia.org/wiki/Braess_paradoxhttp://en.wikipedia.org/wiki/Automated_guided_vehiclehttp://en.wikipedia.org/wiki/Routing#cite_note-1http://en.wikipedia.org/wiki/Autonomous_system_(Internet)http://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Border_Gateway_Protocolhttp://en.wikipedia.org/wiki/Routing#cite_note-2http://en.wikipedia.org/wiki/Hot-potato_routing


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that minimizes the distance through the ISP's own networkeven if that path lengthens the total distance

to the destination.

Consider two ISPs,A and B, which each have a presence in New York, connected by a fast link with

latency 5 ms; and which each have a presence in London connected by a 5 ms link. Suppose both ISPs

have trans-Atlantic links connecting their two networks, butA's link has latency 100 ms and B's has

latency 120 ms. When routing a message from a source inA's London network to a destination in B's

New York network,A may choose to immediately send the message to B in London. This savesA the

work of sending it along an expensive trans-Atlantic link, but causes the message to experience latency

125 ms when the other route would have been 20 ms faster.

A 2003 measurement study of Internet routes found that, between pairs of neighboring ISPs, more than

30% of paths have inflated latency due to hot-potato routing, with 5% of paths being delayed by at least

12 ms. Inflation due to AS-level path selection, while substantial, was attributed primarily to BGP's lack of

a mechanism to directly optimize for latency, rather than to selfish routing policies. It was also suggested

that, were an appropriate mechanism in place, ISPs would be willing to cooperate to reduce latency rather

than use hot-potato routing.[4]

Such a mechanism was later published by the same authors, first for the case of two ISPs[5] and then for

the global case.[6]

[edit]Route Analytics

As the Internet and IP networks become mission critical business tools, there has been increased interest

in techniques and methods to monitor the routing posture of networks. Incorrect routing or routing issues

cause undesirable performance degradation, flapping and/or downtime. Monitoring routing in a network is

achieved usingRoute analytics tools and techniques

NetBIOS

NetBIOS.It provides services related to the session layerof the OSI model allowing applications on

separate computers to communicate over a local area network. As strictly an API, NetBIOS is not

anetworking protocol. Olderoperating systemsran NetBIOS overIEEE 802.2 andIPX/SPXusing

the NetBIOS Frames (NBF) andNetBIOS over IPX/SPX (NBX) protocols, respectively. In modern

networks, NetBIOS normally runs overTCP/IP via the NetBIOS over TCP/IP (NBT) protocol. This results

in each computer in the network having both an IP address and a NetBIOS name corresponding to a

(possibly different) host name.

SYSVOL

In Microsoft Windows, the System Volume (Sysvol) is a shareddirectory that stores the server copy of

the domain's public files that must be shared for common access and replication throughout a domain. The term

SYSVOL refers to a set of files and folders that reside on the local hard diskof eachdomain controllerin a domain

and that are replicated by theFile Replication service (FRS). Network clients access the contents of the SYSVOL tree
http://en.wikipedia.org/wiki/New_York_Cityhttp://en.wikipedia.org/wiki/New_York_Cityhttp://en.wikipedia.org/wiki/Millisecondhttp://en.wikipedia.org/wiki/Londonhttp://en.wikipedia.org/wiki/Routing#cite_note-3http://en.wikipedia.org/wiki/Routing#cite_note-4http://en.wikipedia.org/wiki/Routing#cite_note-5http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=10http://en.wikipedia.org/wiki/Route_analyticshttp://en.wikipedia.org/wiki/Route_analyticshttp://en.wikipedia.org/wiki/Session_layerhttp://en.wikipedia.org/wiki/Session_layerhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Application_programming_interfacehttp://en.wikipedia.org/wiki/Application_programming_interfacehttp://en.wikipedia.org/wiki/Networking_protocolhttp://en.wikipedia.org/wiki/Networking_protocolhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/IEEE_802.2http://en.wikipedia.org/wiki/IEEE_802.2http://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/w/index.php?title=NetBIOS_over_IPX/SPX&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=NetBIOS_over_IPX/SPX&action=edit&redlink=1http://en.wikipedia.org/wiki/TCP/IPhttp://en.wikipedia.org/wiki/NetBIOS_over_TCP/IPhttp://en.wikipedia.org/wiki/IP_addresshttp://www.webopedia.com/TERM/M/Microsoft_Windows.htmlhttp://www.webopedia.com/TERM/M/Microsoft_Windows.htmlhttp://www.webopedia.com/TERM/D/directory.htmlhttp://www.webopedia.com/TERM/D/directory.htmlhttp://www.webopedia.com/TERM/D/domain.htmlhttp://www.webopedia.com/TERM/H/hard_disk.htmlhttp://www.webopedia.com/TERM/H/hard_disk.htmlhttp://www.webopedia.com/TERM/D/domain_controller.htmlhttp://www.webopedia.com/TERM/D/domain_controller.htmlhttp://www.webopedia.com/TERM/F/File_Replication_service.htmlhttp://www.webopedia.com/TERM/F/File_Replication_service.htmlhttp://en.wikipedia.org/wiki/New_York_Cityhttp://en.wikipedia.org/wiki/Millisecondhttp://en.wikipedia.org/wiki/Londonhttp://en.wikipedia.org/wiki/Routing#cite_note-3http://en.wikipedia.org/wiki/Routing#cite_note-4http://en.wikipedia.org/wiki/Routing#cite_note-5http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=10http://en.wikipedia.org/wiki/Route_analyticshttp://en.wikipedia.org/wiki/Session_layerhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Application_programming_interfacehttp://en.wikipedia.org/wiki/Networking_protocolhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/IEEE_802.2http://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/w/index.php?title=NetBIOS_over_IPX/SPX&action=edit&redlink=1http://en.wikipedia.org/wiki/TCP/IPhttp://en.wikipedia.org/wiki/NetBIOS_over_TCP/IPhttp://en.wikipedia.org/wiki/IP_addresshttp://www.webopedia.com/TERM/M/Microsoft_Windows.htmlhttp://www.webopedia.com/TERM/D/directory.htmlhttp://www.webopedia.com/TERM/D/domain.htmlhttp://www.webopedia.com/TERM/H/hard_disk.htmlhttp://www.webopedia.com/TERM/D/domain_controller.htmlhttp://www.webopedia.com/TERM/F/File_Replication_service.html


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by using the NETLOGON and SYSVOL shared folders. Sysvol uses junction points-a physical location on a hard disk

that points to data that is located elsewhere on your disk or otherstorage device-to manage a single instance store.
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Documents

The Role of Domain Controllers