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Branch IP Addressing Deployment Planning

Updated: March 27, 2013

Applies To: Windows Server 2012

Before you deploy a core network, you must plan the following items.

The following sections provide more detail on each of these items.

In TCP/IP networking, routers are used to interconnect the hardware and software used on different physical network segments called subnets. Routers are also used to forward IP packets between each of the subnets. Determine the physical layout of your network, including the number of routers and subnets you need, before proceeding with the instructions in this guide.

In addition, to configure the servers on your network with static IP addresses, you must determine the IP address range that you want to use for the subnet where your core network servers are located. In this guide, the private IP address ranges 192.168.11.1 – 192.168.11.254 and 10.0.1.1 – 10.0.1.254 are used as examples, but you can use any private IP address range that you prefer.

ImportantImportant
After you select the IP address ranges that you want to use for each subnet, ensure that you configure your routers with an IP address from the same IP address range as that used on the subnet where the router is installed. For example, if your router is configured by default with an IP address of 192.168.1.1, but you are installing the router on a subnet with an IP address range of 192.168.11.0/24, you must reconfigure the router to use an IP address from the 192.168.11.0/24 IP address range.

The following recognized private IP address ranges are specified by Internet Request for Comments (RFC) 1918:

  • 10.0.0.0 – 10.255.255.255 (10/8 prefix)

  • 172.16.0.0 – 172.31.255.255 (172.16/12 prefix)

  • 192.168.0.0 – 192.168.255.255 (192.168/16 prefix)

When you use the private IP address ranges as specified in RFC 1918, you cannot connect directly to the Internet using a private IP address because requests going to or from these addresses are automatically discarded by Internet service provider (ISP) routers. To add Internet connectivity to your core network later, you must contract with an ISP to obtain a public IP address.

ImportantImportant
When using private IP addresses, you must use some type of proxy or network address translation (NAT) server to convert the private IP address ranges on your local network to a public IP address that can be routed on the Internet. Most routers provide NAT services, so selecting a router that is NAT-capable should be fairly simple.

For more information, see Planning the deployment of BRANCH1-DHCP1.

For each server in the core network, you must rename the computer and assign and configure a static IPv4 address and other TCP/IP properties for the computer.

For consistency across your network, it is a good idea to use consistent names for servers, printers, and other devices. Computer names can be used to help users and administrators easily identify the purpose and location of the server, printer, or other device. For example, if you have three DNS servers, one in San Francisco, one in Los Angeles, and one in Chicago, you might use the naming convention Location-ServerFunctionNumber:

  • DEN-DNS1. This name represents the DNS server in Denver, Colorado. If additional DNS servers are added in Denver, the numeric value in the name can be incremented, as in DEN-DNS2 and DEN-DNS3.

  • SPAS-DNS1. This name represents the DNS server in South Pasadena, California.

  • ORL-DNS1. This name represents the DNS server in Orlando, Florida.

For this guide, the server naming convention is very simple, and consists of the primary server function and a number. For example, the DHCP server is named BRANCH1-DHCP1.

It is recommended that you choose a naming convention before you install your IP addressing solution using this guide.

Before configuring each computer with a static IP address, you must plan your subnets and IP address ranges. In addition, you must determine the IP addresses of your DNS server(s). If you plan to install a router that provides access to other networks, such as additional subnets or the Internet, you must know the IP address of the router, also called a default gateway, for static IP address configuration.

The following table provides example values for static IP address configuration.

 

Configuration items Example values

IP address

192.168.11.3

Subnet mask

255.255.255.0

Default gateway (Router IP address)

192.168.11.1

Preferred DNS server

192.168.11.2

noteNote
If you plan on deploying more than one DNS server, you can also plan the Alternate DNS Server IP address.

Following are key planning steps before installing the DHCP server role on BRANCH1-DHCP1.

Because DHCP messages are broadcast messages, they are not forwarded between subnets by routers. If you have multiple subnets and want to provide DHCP service for each subnet, you must do one of the following:

  • Install a DHCP server on each subnet

  • Configure routers to forward DHCP broadcast messages across subnets and configure multiple scopes on the DHCP server, one scope per subnet.

In most cases, configuring routers to forward DHCP broadcast messages is more cost effective than deploying a DHCP server on each physical segment of the network.

Each subnet must have its own unique IP address range. These ranges are represented on a DHCP server with scopes.

A scope is an administrative grouping of IP addresses for computers on a subnet that use the DHCP service. The administrator first creates a scope for each physical subnet and then uses the scope to define the parameters used by clients.

A scope has the following properties:

  • A range of IP addresses from which to include or exclude addresses used for DHCP service lease offerings.

  • A subnet mask, which determines the subnet prefix for a given IP address.

  • A scope name assigned when it is created.

  • Lease duration values, which are assigned to DHCP clients that receive dynamically allocated IP addresses.

  • Any DHCP scope options configured for assignment to DHCP clients, such as DNS server IP address and router/default gateway IP address.

  • Reservations are optionally used to ensure that a DHCP client always receives the same IP address.

Before deploying your servers, list your subnets and the IP address range you want to use for each subnet.

Network IDs and host IDs within an IP address are distinguished by using a subnet mask. Each subnet mask is a 32-bit number that uses consecutive bit groups of all ones (1) to identify the network ID and all zeroes (0) to identify the host ID portions of an IP address.

For example, the subnet mask normally used with the IP address 131.107.16.200 is the following 32-bit binary number:

11111111 11111111 00000000 00000000

This subnet mask number is 16 one-bits followed by 16 zero-bits, indicating that the network ID and host ID sections of this IP address are both 16 bits in length. Normally, this subnet mask is displayed in dotted decimal notation as 255.255.0.0.

The following table displays subnet masks for the Internet address classes.

 

Address class  Bits for subnet mask Subnet mask

Class A

11111111 00000000 00000000 00000000

255.0.0.0

Class B

11111111 11111111 00000000 00000000

255.255.0.0

Class C

11111111 11111111 11111111 00000000

255.255.255.0

When you create a scope in DHCP and you enter the IP address range for the scope, DHCP provides these default subnet mask values. Typically, default subnet mask values are acceptable for most networks with no special requirements and where each IP network segment corresponds to a single physical network.

In some cases, you can use customized subnet masks to implement IP subnetting. With IP subnetting, you can subdivide the default host ID portion of an IP address to specify subnets, which are subdivisions of the original class-based network ID.

By customizing the subnet mask length, you can reduce the number of bits that are used for the actual host ID.

To prevent addressing and routing problems, you should make sure that all TCP/IP computers on a network segment use the same subnet mask and that each computer or device has an unique IP address.

When you create a scope on a DHCP server, you specify an IP address range that includes all of the IP addresses that the DHCP server is allowed to lease to DHCP clients, such as computers and other devices. If you then go and manually configure some servers and other devices with static IP addresses from the same IP address range that the DHCP server is using, you can accidentally create an IP address conflict, where you and the DHCP server have both assigned the same IP address to different devices.

To solve this problem, you can create an exclusion range for the DHCP scope. An exclusion range is a contiguous range of IP addresses within the scope’s IP address range that the DHCP server is not allowed to use. If you create an exclusion range, the DHCP server does not assign the addresses in that range, allowing you to manually assign these addresses without creating an IP address conflict.

You can exclude IP addresses from distribution by the DHCP server by creating an exclusion range for each scope. You should use exclusions for all devices that are configured with a static IP address. The excluded addresses should include all IP addresses that you assigned manually to other servers, non-DHCP clients, diskless workstations, or Routing and Remote Access and PPP clients.

It is recommended that you configure your exclusion range with extra addresses to accommodate future network growth. The following table provides an example exclusion range for a scope with an IP address range of 192.168.11.1 - 192.168.11.254 and a subnet mask of 255.255.255.0.

 

Configuration items Example values

Exclusion range Start IP Address

192.168.11.1

Exclusion range End IP Address

192.168.11.15

Certain devices, such as routers, DHCP servers, and DNS servers, must be configured with a static IP address. In addition, you might have additional devices, such as printers, that you want to ensure always have the same IP address. List the devices that you want to configure statically for each subnet, and then plan the exclusion range you want to use on the DHCP server to ensure that the DHCP server does not lease the IP address of a statically configured device.

For example, if the IP address range for a subnet is 192.168.11.1 through 192.168.11.254 and you have ten devices that you want to configure with a static IP address, you can create an exclusion range for the 192.168.11.x scope that includes ten or more IP addresses: 192.168.11.1 through 192.168.11.15.

In this example, you use ten of the excluded IP addresses to configure servers and other devices with static IP addresses and five additional IP addresses are left available for static configuration of new devices that you might want to add in the future. With this exclusion range, the DHCP server is left with an address pool of 192.168.11.16 through 192.168.11.254.

Additional example configuration items for AD DS and DNS are provided in the following table.

 

Configuration items Example values

Network Connect Bindings

Ethernet

DNS Server Settings

RODC1.corp.contoso.com

Preferred DNS server IP address

192.168.11.2

Add Scope dialog box values

  1. Scope Name

  2. Starting IP Address

  3. Ending IP Address

  4. Subnet Mask

  5. Default Gateway (optional)

  6. Lease duration

  1. Primary Subnet

  2. 192.168.11.1

  3. 192.168.11.254

  4. 255.255.255.0

  5. 192.168.11.1

  6. 8 days

IPv6 DHCP Server Operation Mode

Not enabled

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