What is the Difference Between Public and Private IP Addresses?

A unique Internet Protocol (IP) address, known as a public IP address, is assigned to every computer that connects to the Internet. The IP addressing scheme makes it possible for computers to “find each other” online and exchange information. Within a private network, computers use addresses excluded by convention from use on the Internet. The difference between a private IP address and a public IP address then, is that private IP addresses are reserved for private networks, and public IP addresses are reserved for the Internet.

The Internet Assigned Numbers Authority (IANA), a once-autonomous organization, now works within the purview of the Internet Corporation for Assigned Names and Numbers (ICANN). IANA is responsible for overseeing global allocation of IP numbers, among other related protocols. Within the range of publicly available IP addresses are specific, excluded ranges withheld for private network use. These private IP ranges are as follows:

• 10.0.0.0 … 10.255.255.255
• 172.16.0.0 … 172.31.255.255
• 192.168.0.0 … 192.168.255.255

Computers within a private network are each assigned a unique address in order to exchange files and share resources with one another. The network router, which routes information, will pass data back and forth among the connected computers, using the respective addresses. But how do computers on a private network connect to the Internet?

 

Assuming the network has Internet connectivity, the computer connected to the digital subscriber line (DSL) modem is assigned a public IP address by the Internet Service Provider (ISP). This single public IP address is used to identify the network on the Internet. Now the network’s router acts as a gatekeeper between the private network and the public Internet. Using a built-in Network Address Translator (NAT), the router passes requests to the Internet using the assigned public IP address. Returning data is routed back to the public IP address, with the router determining which private IP address requested the information. In essence, the private IP address is daisy-chained to the public IP address through processes in the router.

A public IP address can be static or dynamic. A static public IP address does not change and is used primarily for hosting webpages or services on the Internet. Some gamers also prefer static IPs for interactive gaming. A dynamic public IP address is chosen from a pool of available addresses and changes each time one connects to the Internet. Most people have a dynamic public IP address, as it is the standard type of public IP address assigned when purchasing Internet connectivity.

Various freeware programs are available online that will display your computer’s assigned public IP address for you. To see private IP addresses you can open your router’s configuration dialogs, or if using Windows XP, type ipconfig at the command prompt. The command prompt is available through Start -> All Programs -> Accessories -> Command Prompt. To leave the command prompt window, type exit.

 

 

Source: What is the Difference Between Public and Private IP Addresses?

Reconcile on DHCP Scope Does Not Work Correctly for BOOTP Client

When you perform a reconcile to synchronize the database with the registry, after deleting the DHCP database, all reservations are put back into the database but the media access control addresses are incorrect.
The DHCP server sends a NACK or does not respond to BOOTP requests from a client as the request is based on the media access control address.

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CAUSE

When the BOOTP request is processed by the DHCP server, the server matches the r…

When the BOOTP request is processed by the DHCP server, the server matches the requested media access control address in the request to an IP address and marks the reservation as in use. After performing a reconcile, the media access control address is no longer correct in the DHCP database and the client requests are either receive a NACK or the DHCP server does not respond to the BOOTP request.

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RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Wi…

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

152734 (http://support.microsoft.com/kb/152734/EN-US/ ) How to Obtain the Latest Windows NT 4.0 Service Pack

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STATUS

Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT…

Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.

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APPLIES TO

• Microsoft Windows NT Server 4.0, Terminal Server Edition
• Microsoft Windows NT Server 4.0 Standard Edition
• Microsoft Windows NT Server 4.0 Enterprise Edition
• Microsoft BackOffice Small Business Server 4.0
• Microsoft BackOffice Small Business Server 4.0a

Source: Reconcile on DHCP Scope Does Not Work Correctly for BOOTP Client

How DHCP server works in Windows Network

1. DHCP server uses database file named dhcp.mdb stored in C:\windows\system32\dhcp folder.
2. A backup copy the DB in the C:\windows\system32\dhcp\backup folder by default.
3. During service startup, If the original DB file is not found the service loads the DB from backup folder
4. DHCP service writes to the registry whenever a dhcp lease is handed out to clients
5. The Registry path is HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DhcpServer\Configuration
6. During proper service shutdown, it takes backup copies of both dhcp.mdb and Registry
7. The backup information of Registry is stored in Dhcpcfg file in DHCP DB folder
8. Whenever a successful lease is released, it first writes the details to registry and those later gets updated to DB
9. When run reconciliation, the service will cross checks the lease entries in Registry and DB and reports for any inconsistences which will be fixed by eliminating extra entries in registry that doesn’t match with entries in DB
10. You can configure the Conflict detection to a non-zore value in IPv4 Properties Advanced tab such that DHCP server verifies the IP-address existene on the network by pinging the IP-Address  before handing over to the clients.

How to Restore a Corrupted DHCP Database File

This article discusses methods that may be used to recover a corrupted Dynamic Host Configuration Protocol (DHCP) database.

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MORE INFORMATION

Important This section, method, or task contains steps that tell you how to modi…

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 (http://support.microsoft.com/kb/322756/ ) How to back up and restore the registry in Windows

The following event log messages appear on a computer running Windows NT Server versions 3.51 and 4.0 when the DHCP database has been corrupted:

Event ID: 1014
Source: DhcpServer
Description: The Jet database returned the following Error: -510.

-or-

Event ID: 1014
Source: DhcpServer
Description: The Jet database returned the following Error: -1022.

-or-

Event ID: 1014
Source: DhcpServer
Description: The Jet database returned the following Error: -1850.

If you use Jet.exe to compact the DHCP database, you will not resolve the issue.
For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

153476 (http://support.microsoft.com/kb/153476/ ) Windows NT 3.51 DHCP Server Stops Assigning IP Addresses to Clients

The DHCP database is contained in the Dhcp.mdb file located in the %SystemRoot%\System32\Dhcp folder. The DHCP server uses this file to record and store information concerning active leases and reservations. Most of this information is also contained in the following registry key:

Windows NT 4.0:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DHCPServer\Configuration

Windows 2000:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DhcpServer\Configuration

Whenever the DHCP service shuts down correctly, it makes a backup copy of both the database file (Dhcp.mdb) and the registry key. The backup information from the registry is contained in the file Dhcpcfg. For Windows NT 3.51, the file Dhcp.mdb is located in the %SystemRoot%\System32\Dhcp\Backup\Jet folder. In Windows NT 4.0, the file Dhcp.mdb is located in the %SystemRoot%\System32\Dhcp\Backup\Jet\New folder. Both versions of Windows NT store the Dhcpcfg file in the %SystemRoot%\System32\Dhcp\Backup folder.
To recover a corrupted DHCP database, use one of the following methods:

· Restore a backup copy of the database file, Dhcp.mdb
- or-

· Generate a new database file using the DHCP Configuration registry key.

Restoring a backup copy of the database file is the recommended method because you will not lose information when you use it.
After you recover your database file using one of the methods mentioned earlier, you must reconcile the information between the database file and the registry information.
NOTE: The following steps assume that your DHCP server will not start because of a corrupted DHCP database. If your DHCP server starts, but the database is corrupted, you have to start by stopping the service.
To stop the DHCP server service, type the following at a command prompt:
net stop dhcpserver

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Restoring a Backup Copy of the Database

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 (http://support.microsoft.com/kb/322756/ ) How to back up and restore the registry in Windows

1. Move the files from your existing DHCP folder to a different location, being careful to keep the DHCP folder structure intact. For example, type the following at a command prompt and press ENTER after each line:
md c:\Olddhcp move %SystemRoot%\system32\DHCP\*.* C:\Olddhcp

2. Remove the corrupted database file.

3. Copy the backup database file into the DHCP folder by typing the following at a command prompt, and then pressing ENTER:

o Windows NT 3.51
copy %SystemRoot%\system32\dhcp\backup\jet\dhcp.mdb %SystemRoot%\system32\dhcp\dhcp.mdb

o Windows NT 4.0
copy %SystemRoot%\system32\dhcp\backup\jet\new\dhcp.mdb %SystemRoot%\system32\dhcp\dhcp.mdb

If your computer is running Microsoft Windows 2000, modify the following registry key to restore the DHCP server:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\Parameters

Change the RestoreFlag REG_DWORD value in this registry key to 1.
You may also choose to restore the Dhcp.mdb file to the %SystemRoot%\System32\Dhcp folder from a tape backup or other backup media.
Because you are using an existing database file, whether you restore it from backup media or the backup folder, you must use the Jetpack utility to compress it.
For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

145881 (http://support.microsoft.com/kb/145881/EN-US/ ) How to Use Jetpack.exe to Compact a WINS or DHCP Database

The above procedure should allow the service to start, but if your scope information is missing, you must use a backup copy of the Dhcpcfg registry file to restore your scope and reservation information. See steps 5 through 11 in the "From the New DHCP Server" section of the following article:
For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

130642 (http://support.microsoft.com/kb/130642/ ) How to Move a DHCP Database to Another Windows Server

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Generating a New Database File

1. Move the files in your existing DHCP folder to a different location, being careful to keep the DHCP folder structure intact. For example, type the following at a command prompt, pressing ENTER after each line:
md c:\olddhcp move %SystemRoot%\system32\dhcp\*.* c:\olddhcp

2. Select the next step from the following list, depending on which version of Windows NT Server you are using:
Windows NT Server 3.51:
Expand a new copy of System.mdb from the original Windows NT Server source media by inserting your original Windows NT Server 3.51 CD into your CD-ROM drive. To do so, type the following at a command prompt, and then press ENTER:
expand D:\I386\System.md_ %SystemRoot%\System32\Dhcp\System.mdb
where D: is your CD-ROM drive and i386 is your platform.
Windows NT Server 4.0:
Restart the DHCP server with an empty DHCP folder. Windows NT 4.0 and Windows 2000 do not use a System.mdb file.

The above procedure should allow the service to start, but if your scope information is missing, you must use a backup copy of the Dhcpcfg registry file to restore your scope and reservation information. See steps 5 through 11 in the "From the New DHCP Server" section of the following article:
For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

130642 (http://support.microsoft.com/kb/130642/ ) How to Move a DHCP Database to Another Windows Server

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Reconciling DHCP Information

After you generate a new database file, you may notice that the scope information is present, but no active leases are displayed. To regain the active leases, you must reconcile the database with the information in the registry using the following steps:

1. From DHCP Manager, click your scope, and then click Active Leases on the Scope menu.

2. In the Active Leases dialog box, click Reconcile.

3. Click OK. Your active leases will appear in the Active Leases dialog box.

NOTE: When you view the properties for a client lease, the computer name will be listed as the IP address of the lease and an arbitrary hexadecimal value will be listed as the client identifier. These will be replaced with the appropriate information as the clients renew their leases.
Repeat the above procedure for each scope for which you must reconcile leases.
If your DHCP server is Windows NT Server 4.0 SP2 or later, you must turn on IP Conflict Detection as described in the following article:

161430 (http://support.microsoft.com/kb/161430/EN-US/ ) Detecting and Flagging Duplicate IP Addresses

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APPLIES TO

· Microsoft Windows 2000 Server

· Microsoft Windows 2000 Advanced Server

· Microsoft Windows NT Server 3.51

· Microsoft Windows NT Server 4.0 Standard Edition

 

Source: How to Restore a Corrupted DHCP Database File

Troubleshooting DHCP servers: Dynamic Host Configuration Protocol (DHCP)

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Troubleshooting DHCP servers

What problem are you having?

• The DHCP server is stopped.
• The DHCP server is unable to provide service to clients.
• One of two DHCP servers on the same subnet is not servicing clients.
• The DHCP server appears to have suffered some data corruption or loss.
• The server appears to be affected by another problem not described above.

The DHCP server is stopped.

• Cause: The DHCP server has not been authorized to operate on the network.
• Solution: Authorize the DHCP server in the enterprise where it is being used.
• See also: Authorizing DHCP servers; Authorize a DHCP server in Active Directory; Delegate ability to authorize DHCP servers to a non-enterprise administrator
• Cause: Configuration details might be incorrect or missing at the server.
• Solution: If you have just completed setting up or administering the DHCP server, you might want to review the provided checklist to see if you have missed a crucial step in the installation process.
  To help prevent the most common types of problems, review DHCP best practices for tips on deploying and managing your servers.
  Because many DHCP failures are first detected as client-side errors, you might want to start by investigating the problem there.
• See also: Checklist: Installing a DHCP server; DHCP Best Practices; Troubleshooting DHCP clients
• Cause: The DHCP server has been stopped.
• Solution: Check the system event log and DHCP server audit log files for details.
  When the DHCP Server service either stops or cannot start, useful explanatory information about the source of the service failure or shutdown can generally be found in these logs.
• See also: Audit logging; Analyzing server log files; Using the Event Viewer snap-in; Search for specific events

The DHCP server is unable to provide service to clients.

• Cause: The server is a multihomed computer and is not providing service on one or more of its network connections.
• Solution: Review Windows Server 2003 DHCP binding defaults for network connections based on whether you have elected to either statically or dynamically configure TCP/IP for any or all installed connections on the server computer. Also, review an example of multihomed DHCP server configuration to see if you have missed any critical details.
• See also: Multihomed DHCP servers; Selectively set DHCP server bindings for network connections
• Cause: Scopes or superscopes on the DHCP server have not been either configured or activated for use.
• Solution: Add scopes and make sure that they are correctly configured along with any DHCP scope options that need to be assigned for client use.
• See also: Configuring scopes; Create a new scope; Assign a scope-based option
• Cause: The server is located on a different subnet as some of its clients and is not providing service to clients on remote subnets.
• Solution: If you are using a DHCP server in a routed network, you might want to review issues related to DHCP relay agents and the appropriate use of superscopes.
• See also: DHCP/BOOTP Relay Agents; Using superscopes; Create a superscope
• Cause: The scope in use is full and can no longer lease addresses to requesting clients.
• Solution: If the DHCP server does not have IP addresses available to provide to its clients, it returns DHCP negative acknowledgment messages (DHCPNAKs) to them. When this occurs, consider the following possible solutions:

1. Expand the address range by increasing the End IP address for the current scope.
2. Create a new additional scope and a superscope, then add the current scope and the new scope to the superscope.
3. Create a new scope or extend the range. Optimally, you could renumber your current IP network. Deactivate the old scope as needed, and then configure and activate the new one.
4. Reduce the lease duration. This can help to expedite the reclaiming of lapsed scope addresses.
   Other DHCP-related procedures and techniques might also help to accelerate or ease the transition from an existing scope being retired to a new scope created to take its place at the server. These include deleting client leases from the scope being retired, excluding addresses from that scope, and then deactivating it once the new scope has been activated. This ensures that the DHCP client obtains leasing from the new scope.

• See also: Managing leases; Removing scopes; Delete a client lease; Exclude an address from a scope; Activate a scope; Deactivate a scope
• Cause: The range of IP addresses being offered by the DHCP server is in conflict with the range of addresses being offered by another DHCP server on the network.
  You can confirm that this is the likely cause if DHCP server logs still indicate that DHCP negative acknowledgment messages (DHCPNAKs) are being returned to requesting clients or if you have tried unsuccessfully at the client to renew its lease manually.
• Solution: Modify the scope address pool for the scopes at each DHCP server to ensure that scope IP addresses do not overlap. You can add exclusions to the scopes as necessary, delete client leases, and temporarily enable server-side conflict detection to assist in solving the problem.
• See also: Delete a client lease; Exclude an address from a scope; Enable address conflict detection; DHCP Best Practices

One of two DHCP servers on the same subnet is not servicing clients.

• Cause: The DHCP server is not authorized in Active Directory.
• Solution: If the DHCP server is a domain member, authorize the server in Active Directory.
  In some circumstances you might accidentally have a standalone server and a domain member server on the same subnet. When the standalone server detects the domain member server, it attempts to verify that it is authorized in Active Directory. Even if a domain controller resides on the same subnet as the standalone DHCP server, the DHCP server cannot verify its status with the domain controller because the DHCP server is not a domain member. When the standalone server is unable to access a domain controller to discover whether it is authorized, it stops servicing clients and displays the red icon in the DHCP console that indicates the server is unauthorized. If you want the standalone server to service clients on the subnet, remove the authorized DHCP server from the subnet.
• See also: Authorizing DHCP servers; Authorize a DHCP server in Active Directory; DHCP console icons reference

The DHCP server appears to have suffered some data corruption or loss.

• Cause: The DHCP server database has become corrupted or is missing server data, possibly reporting JET database errors.
• Solution: Use DHCP server data recovery options to restore the database and correct any of the reported errors. You can also use the Reconcile feature in the DHCP console to verify and reconcile any database inconsistencies that the server is able to find.
• See also: Restoring server data; The DHCP database; Reconciling scopes; Reconcile the DHCP database; Reconcile a scope

The server appears to be affected by another problem not described above.

• Cause: My problem is not described above.
• Solution: Search the Microsoft Web site for updated technical information that might relate to the problem you have observed. You can obtain information and instructions that pertain to your current problem or issue.
  If you have connection to the Internet, the latest updates for members of the Windows Server 2003 family are available at the Microsoft Web site.
• See also: DHCP updated technical information; DHCP; Using the Windows Deployment and Resource Kits; Microsoft Web site

 

Source: Troubleshooting DHCP servers: Dynamic Host Configuration Protocol (DHCP)

Maintaining DHCP Server

Modify the network/NIC Bindings:  required for configuring the DHCP server operate in chosen networks:

1. Go to DHCP console
2. Right click on the DHCP server
3. Click on “Add/Remove Bindings”
4. Select the appropriate/required network connections from the available networks list

 

Maintain DHCP Database:

Locate DB location

1. In DHCP console, right click on the server and choose Properties
2. The properties pane will display the current location of its DB and DBs Backup
1. The Default location of DB is: C:\Windows\System32\dhcp
2. The Default location of DB Backup is: C:\Windows\System32\dhcp\backup
3. Database file is named as dhcp.mdb and there will be other files names dhcpcfg, dhcp.pat and text files with random names

How DHCP service uses its Database and Registry:

The DHCP database is contained in the Dhcp.mdb file located in the %SystemRoot%\System32\Dhcp folder. The DHCP server uses this file to record and store information concerning active leases and reservations. Most of this information is also contained in the following registry key:

Windows NT 4.0:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DHCPServer\Configuration

Windows 2000:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DhcpServer\Configuration

Whenever the DHCP service shuts down correctly, it makes a backup copy of both the database file (Dhcp.mdb) and the registry key. The backup information from the registry is contained in the file Dhcpcfg.

1. For Windows NT 3.51, the file Dhcp.mdb is located in the %SystemRoot%\System32\Dhcp\Backup\Jet folder.
2. In Windows NT 4.0, the file Dhcp.mdb is located in the %SystemRoot%\System32\Dhcp\Backup\Jet\New folder.
3. Both versions of Windows NT store the Dhcpcfg file in the %SystemRoot%\System32\Dhcp\Backup folder.

 

DHCP DB Backup and Restore:

1. DHCP by default backups the DB at every hour
2. During DHCP service startup, if actual DB is not found, DHCP automatically loads the DB from the Backup DB path
3. You can manually backup and restore the DB from the DHCP server right click options
4. DHCP DB restore, requires a DHCP service to be restarted in order for the changes to take effect

To recover a corrupted DHCP database, use one of the following methods:

• Restore a backup copy of the database file, Dhcp.mdb
  - or-
• Generate a new database file using the DHCP Configuration registry key.

Restoring a backup copy of the database file is the recommended method because you will not lose information when you use it. After you recover your database file using one of the methods mentioned earlier, you must reconcile the information between the database file and the registry information.

Monitoring DHCP Status:

 

1. Right the DHCP server and click on “Display Statistics”,
2. In cases of any issues you’ll see the Requests or Nacks piling up in server properties
3. You can view the statistics at Scope level as well
4. DHCP reconciliation is a process of  

DHCP Auditing:
1. To enable DHCP Auditing: Goto  DHCP server > IPv4 > Right click and select Properties
2. check the checkbox “Enable DHCP Audit Logging”
3. Click on Advanced tab, there you can change where the auditing log files are getting saved. The default would  C:\Windows\System32\dhcp
4. 

DHCP Access Delegations:

On DHCP server contains two user groups to provision access rights to users/administrators

1. DHCP Administrators
2. DHCP Users

 

 

 

 

 

 

 

 

 

 

 

Source: How to Restore a Corrupted DHCP Database File

Networking DHCP Servers and Networks in Windows Server 2008 R2 Network

A DHCP server and Clients communication starts off of broadcast packets from clients looking for DHCP servers.  However, the routers (default gateways that directs the network traffic) doesn’t support broadcast communication across the networks thus kills the broadcast packets. 

 

This makes DHCP servers restricted only to the network that they are in.  In order to make DHCP server serve the requests from clients across various network segments/subnets, we have below options:

1. Put DHCP server in each of the network segment/subnet
2. Use RFC 1542 compliant Routers that support broadcasting communication across segments
3. Use DHCP relay agents  (is a device, service most often on the router itself, role in 2K8 R2 server,  )

Implementing DHCP Relay Agent service on Windows Server 2008 R2:

1. Launch the RRAS (Routing and Remote Access Server) console from Administrative Tools
2. In console navigate to IPv4 > General > right click and choose “New Routing Protocol”
3. Select “DHCP Relay Agent” from the list of available routing protocols
4. Then you’ll see the “DHCP Relay Agent” listed under IPV4
5. Then associate the Agent with the network that you want it to relay the DHCP requests by doing right click then “New Interface”
6. Select the network interface of that network where you’d like to have this agent 
7. Set the values for DHCP Relay Agent DHCP interface
8. Go to the properties of the Relay agent
9. Specify the actual DHCP server(s) address to which the relay agent should direct the requests

Configuring DHCP Server in Windows Server 2008 R2

The first step after installing DHCP server is to authorize that server to serve the client requests.

 

Authorize DHCP server:

1. In DHCP management console, select the server, right click and click “Authorize”
2. From the same place you can have an active DHCP server to be “Unauthorize”

Creating a new DHCP Scope:

 

1. A scope is a range of IP addresses assigned to computers requesting dynamic IP address
2. You can create a new scope for IP version 4/6 that you choose and do a right click and then clicking the “New Scope”
3. That open up a New Scope Wizard as shown below
4. Click next on the Welcome screen
5. Specify a name to the scope and click Next
6. Specify the IP-address range that you want this scope to cover
   1. Starting and Ending IP addresses form the set of IP address to be used by the Scope
   2. Choose the subnet mask as per your network classification plan, to support no.of IP-addresses in the selected range for this scope. 
   3. In this example I choose the subnet mast 255.255.255.0 which means that 24 bits out of 32bit subnet mask are used for network identification whereas the remaining 8 bits are used to form the IP-addresses that count to 256 (i.e., 2^8)
7. In the next screen specify IP-addresses or range of IP-addresses that need to be excluded from this scope
8. Specify the lease duration, default is 8 days as shown below
   1. Set longer durations for desktops Subnets
   2. Set shorter durations for portable PCs subnets
9. Specify the additional DHCP options that include setting DNS, WINS servers details to be used for that subnet. The scope level DHCP options override the options set at DHCP server level
10. You can configure the scope level DHCP options from the DHCP console at a later point as well, if you choose no, Click finish on the next screen
11. Finally, you need to activate the new scope in order to bring it in to the operations

Configure DHCP server communication with DNS servers:

Integrating DHCP with NAP (Network Access Protection)  server:

Subnetting, purpose of it and how it works

A subnetwork, or subnet, is a logically visible subdivision of an IP network.^[1] The practice of dividing a network into two or more networks is called subnetting.

Subnet mask:

A subnet mask separates the IP address into the network and host addresses (<network><host>). Subnetting further divides the host part of an IP address into a subnet and host address (<network><subnet><host>). It is called a subnet mask because it is used to identify network address of an IP address by performing bitwise AND operation on the netmask.

 

 

 

Subnet Mask is made by setting

1. network bits to all "1"s and
2. setting host bits to all "0"s

Within a given network, two host addresses are reserved for special purpose.

1. "0" address is assigned a network address and
2. "255" is assigned to a broadcast address

and they cannot be assigned to a host.  For example, applying the Class C subnet mask to our IP address 216.3.128.12 produces the following network address:

IP:          1101 1000 . 0000 0011 . 1000 0000 . 0000 1100  (216.003.128.012)
Mask:        1111 1111 . 1111 1111 . 1111 1111 . 0000 0000  (255.255.255.000)
             ---------------------------------------------
NetworkAddr: 1101 1000 . 0000 0011 . 1000 0000 . 0000 0000  (216.003.128.000)

 

 

CIDR – Classless Inter Domain Routing

Classless InterDomain Routing (CIDR) was invented to keep the Internet from running out of IP Addresses. The IPv4, a 32-bit, addresses have a limit of 4,294,967,296 (2³²) unique IP addresses. The classful address scheme (Class A, B and C) of allocating IP addresses in 8-bit increments can be very wasteful.

With classful addressing scheme, a minimum number of IP addresses allocated to an organization is 256 (Class C). Giving 256 IP addresses to an organization only requiring 15 IP addresses is wasteful. Also, an organization requiring more than 256 IP addresses (let’s say 1,000 IP addresses) is assigned a Class B, which allocates 65,536 IP addresses. Similarly, an organization requiring more than 65,636 (65,634 usable IPs) is assigned a Class A network, which allocates 16,777,216 (16.7 Million) IP addresses. This type of address allocation is very wasteful.

With CIDR, a network of IP addresses is allocated in 1-bit increments as opposed to 8-bits in classful network. The use of a CIDR notated address can easily represent classful addresses (Class A = /8, Class B = /16, and Class C = /24). The number next to the slash (i.e. /8) represents the number of bits assigned to the network address. The example shown above can be illustrated with CIDR as follows:

   216.3.128.12, with subnet mask of 255.255.255.128 is written as
   216.3.128.12/25

   Similarly, the 8 customers with the block of 16 IP addresses can be
   written as:

   216.3.128.129/28, 216.3.128.130/28, and etc.

With an introduction of CIDR addressing scheme, IP addresses are more efficiently allocated to ISPs and customers; and hence there is less risk of IP addresses running out anytime soon. For detailed specification on CIDR, please review RFC 1519. With introduction of additional gaming, medical, applicance and telecom devices requiring static IP addresses in addition to more than 6.5 billion (July 2006 est.) world population, the IPv4 addresses with CIDR addressing scheme will eventually run out. To solve shortage of IPv4 addresses, the IPv6 (128-bit) address scheme was introduced in 1993.

 

 

Examples of commonly used netmasks for classed networks are 8-bits (Class A), 16-bits (Class B) and 24-bits (Class C), and classless networks are as follows:

 

Class	Address	# of Hosts	Netmask (Binary)	Netmask (Decimal)
CIDR	/4	240,435,456	11110000 00000000 00000000 00000000	240.0.0.0
CIDR	/5	134,217,728	11111000 00000000 00000000 00000000	248.0.0.0
CIDR	/6	67,108,864	11111100 00000000 00000000 00000000	252.0.0.0
CIDR	/7	33,554,432	11111110 00000000 00000000 00000000	254.0.0.0
A	/8	16,777,216	11111111 00000000 00000000 00000000	255.0.0.0
CIDR	/9	8,388,608	11111111 10000000 00000000 00000000	255.128.0.0
CIDR	/10	4,194,304	11111111 11000000 00000000 00000000	255.192.0.0
CIDR	/11	2,097,152	11111111 11100000 00000000 00000000	255.224.0.0
CIDR	/12	1,048,576	11111111 11110000 00000000 00000000	255.240.0.0
CIDR	/13	524,288	11111111 11111000 00000000 00000000	255.248.0.0
CIDR	/14	262,144	11111111 11111100 00000000 00000000	255.252.0.0
CIDR	/15	131,072	11111111 11111110 00000000 00000000	255.254.0.0
B	/16	65,534	11111111 11111111 00000000 00000000	255.255.0.0
CIDR	/17	32,768	11111111 11111111 10000000 00000000	255.255.128.0
CIDR	/18	16,384	11111111 11111111 11000000 00000000	255.255.192.0
CIDR	/19	8,192	11111111 11111111 11100000 00000000	255.255.224.0
CIDR	/20	4,096	11111111 11111111 11110000 00000000	255.255.240.0
CIDR	/21	2,048	11111111 11111111 11111000 00000000	255.255.248.0
CIDR	/22	1,024	11111111 11111111 11111100 00000000	255.255.252.0
CIDR	/23	512	11111111 11111111 11111110 00000000	255.255.254.0
C	/24	256	11111111 11111111 11111111 00000000	255.255.255.0
CIDR	/25	128	11111111 11111111 11111111 10000000	255.255.255.128
CIDR	/26	64	11111111 11111111 11111111 11000000	255.255.255.192
CIDR	/27	32	11111111 11111111 11111111 11100000	255.255.255.224
CIDR	/28	16	11111111 11111111 11111111 11110000	255.255.255.240
CIDR	/29	8	11111111 11111111 11111111 11111000	255.255.255.248
CIDR	/30	4	11111111 11111111 11111111 11111100	255.255.255.252

 

 

Reference:

What is Subnet Mask?

Installing DHCP Server on Windows Server 2008 R2

Pre-requisite setup:

As a well known case, that all the network service servers should be using the Static IP-Address. DHCP server checks the status of static IP-address and warns you if it’s not the case.

You need “Enterprise Administrator” access level for authorizing the newly installed DHCP Server as valid DHCP server on the network. This can be done at a later part from the DHCP Server Management Console

 

DHCP Server Installation:

DHCP Server is a server role in Windows Server 2008 R2.  You can add/Remove this role via Server Manager > Roles Section.  Below are the sequence of steps that you do in DHCP server install from Server Manager

 

1. Launch Server Manager
2. Click Roles
3. Click on “Add Roles” from right click or from the roles pane
4. You’ll be in “Add Roles Wizard” window
5. In “Server Roles” section, Select “DHCP Server” from the list of available roles and click Next
6. In “DHCP Server” section, Click Next to “Introduction to DHCP Server”
7. In “Network Connection Bindings” section, Select the NICs that you would like to be bound for serving DHCP requests from list in “Network Connections” available on that system and click next
8. In “IPv4 DNS Settings” section
   1. Verify the default populated DNS suffix/domain name in  “Parent Domain” textbox and update if needed
   2. Specify the value for “Preferred DNS Server IPv4 Address”  and click on “Validate” button to ensure that it’s indeed a IPV4 DNS server on that address
   3. Also, specify the value for optional parameter “Alternate DNS Server IPv4 Address” and click on “Validate” button to ensure that it’s indeed a IPV4 DNS server on that address
   4. Click Next

   

9. In “IPv4 WINS Settings” section, depending upon your network requirements to support NetBIOS clients choose either to enable or disable the WINS support
   1. WINS is not required for applications on this network
   2. WINS is required for applications on this network, then specify the WINS server details
   3. Click Next

   

10. In “DHCP scopes” section, you can add DHCP scopes.  You can also do this from DHCP Server Console at a later point
11. In “DHCPv6 Stateless Mode”  select either,
    1. Enable DHCPv6 stateless mode for this server
       1. IPv6 clients will be automatically configured without using the DHCP server.
    2. Disable DHCPv6 stateless mode for this server
       1. After installing DHCP Server you can configure the DHCPv6 mode using the DHCP Management Console 

    

12. In “IPv6 DNS Settings” section
    1. Verify the default populated DNS suffix/domain name in “Parent Domain” textbox and update if needed
    2. Specify the value for “Preferred DNS Server IPv6 Address” and click on “Validate” button to ensure that it’s indeed a IPV6 DNS server on that address
    3. Also, specify the value for optional parameter “Alternate DNS Server IPv6 Address” and click on “Validate” button to ensure that it’s indeed a IPV6 DNS server on that address
    4. In case, if you are NOT using IPv6 then you need to specify the ::1 (i.e., localhost in IPv6 terms) for “Preferred DNS Server IPv6 Address” in order have the next button enabled
    5. Click Next
13. In “Authorize DHCP Server” section, you need to authorize the DHCP Server install on this server for this you need to be an Enterprise Administrator, you’ll have below option for choose Authorization
    1. Use Current Credentials
    2. Use Alternate Credentials
    3. Skip Authorization of this DHCP server in AD DS
       1. Note: if you choose Skip authorization that DHCP server doesn’t take part in servicing clients. The DHCP server must be authorized in AD DS before it can serve clients.

    

14. On Confirmation screen, review the settings, manage if needed using Previous buttons
15. Click Install
16. Click Close on Results screen if the install is successful

Images Source and References:

1. How to Install and Configure Windows Server 2008 DHCP Server
2. Running Windows Server 2008 R2 – Installing and Creating the Lab Domain Controller (Part 2)