Wireless Networking

Together with Domain Name System (DNS), the Dynamic Host Configuration Protocol (DHCP) serves as a basic foundation of a Microsoft Windows Server 2003 network infrastructure. DHCP server provides hosts with an Internet Protocol (IP) configuration needed to communicate with other computers on the network.

DHCP is an IP standard designed to reduce the complexity of administering these address configurations. By issuing leases from a central database, DHCP server automatically manages address assignment and configures other essential settings for your network clients.

• When a DHCP server is unavailable, such clients automatically adopt an alternate configuration or an Automatic Private IP Addressing (APIPA) address.
• DHCP server provides automatic assignment of IP addresses. The administrator needs to define the scope (the pool of IP addresses)
• Clients lease addresses for a specific length of time from the DHCP server. Once 50% of the lease has expired, the clients will attempt to renew the same IP address. The DHCP server will renew addresses for another lease period.
• The DHCP server will tremendously time-save for the network administrator
• One DHCP server can serve multiple subnets through DHCP relay agents or bootstrap protocol (BOOTP) forwarding
• Windows server 2003 can serve almost all DHCP clients including BOOTP clients. BOOTP clients are not turned on by default

DHCP server Scopes

A DHCP scope is a pool of IP addresses within a logical subnet, for example 192.168.100.1 through 192.168.100.220, that the DHCP server can assign to clients. Scopes provide the essential means for the DHCP server to manage distribution and assignment of IP addresses and of any related configuration parameters to clients on the network.

• DCHP server scope specifies the range of addresses available for lease. An IP address within a defined scope that is offered to a DHCP client is known as a lease. Each lease has a specified duration, and the clients must periodically renew the lease.
• An exclusion range can be set within the range of defined scope if you don’t want to lease to DHCP clients. Exclusion range assure that the DHCP server does not offer the exclusion range to DHCP clients
• One DHCP scope is for one subnet
• One DHCP server can serve multiple subnets
• Can supply additional configuration options such as default gateway; DNS servers; WINS servers
• Can reserve addresses by MAC address. This feature is good for servers; printers; and other devices that require static addresses
• Server can hold scopes for remote subnets. Since DHCP is a broadcast based, while routers by default block the broadcast you can use either RFC 1542 compliant routers or DHCP relay agents to forward the broadcast.

Load balance rule

To provide fault tolerance for the DHCP service within a given subnet, you might want to configure two DHCP servers to assign addresses for the same subnet. With two DHCP servers deployed, if one DHCP server is unavailable, the other DHCP server can take its place and continue to lease new addresses or renew existing clients. For balancing DHCP server use in this case, a good practice is to use the 80/20 rule to divide the scope addresses between the two DHCP servers. If DHCP Server #1 is configured to make available most (approximately 80 percent) of the addresses, DHCP Server #2 can be configured to make the other addresses (approximately 20 percent) available to clients.

How the process of DHCP server to the clients?

• DHCP clients broadcast DHCPDISCOVER packet to the network
• DHCP server then responds with DHCPOFFER packet
• DHCP clients broadcast DHCPREQUEST packet
• DHCP server responds with DHCPACK packet
• After 50% lease time, DHCP clients will attempt to renew address with a DHCPREQUEST directed to the DHCP server
• DHCP server responds with DHCPACK again

Configuring the Client

To configure a client to receive its IP address information from a DHCP server, open the Internet Protocol (TCP/IP) Properties dialog box for the appropriate network connection. By selecting the “Obtain an IP Address Automatically” option, you enable the client to obtain from the DHCP server an IP address, subnet mask, and all DHCP options except for DNS options. To configure the client to receive DNS options from the DHCP server, select the Obtain DNS Server Address Automatically option.

Migrating from APIPA or Alternate Configurations

If a client has already been configured to obtain an IP address and DNS server address automatically, and the network is not using ICS, you merely need to renew the IP configuration to apply the settings from the newly configured DHCP server.

To renew a configuration, enter the ipconfig /renew command at the command prompt. Alternatively, you can restart the client computer, and the new IP configuration from DHCP server is applied as the computer reboots.

Migrating from an ICS Connection

ICS is a shared dial-up connection on a server that provides Internet access to network clients and automatically configures client computers with an address in the 192.168.0.x subnet range. Because this service competes with the DHCP Server service, you should delete any shared (ICS-enabled) dial-up connections on the server and restart the server computer before installing the DHCP Windows component or adding the DHCP Server role.

The above procedure frequently will not work as expected. ICS clients are already configured to obtain an IP address automatically, so in theory, they require no reconfiguration beyond a simple reboot if you want to migrate to receive the IP from DHCP server. However, you might find that in practice, ICS clients stubbornly cling to their ICS addresses even after DHCP is deployed. To prevent such complications, you can first apply a manual (static) address to the client computers after the ICS connection is deleted; this procedure breaks the ICS connection. Then restart the client computers. After the clients restart, they will migrate cleanly to receive the IP from DHCP server as soon as you reconfigure them to obtain an address automatically.

You know that all of the wireless Access Point or Wireless routers such as Linksys wireless routers; D-Link wireless routers or Belkin wireless routers; can serve as DHCP server to supply the computers on the wireless networking with the IP addresses for network communication.

DHCP servers use private IP address instead of public IP addresses (registered IP address), since private IP addresses are not routable to the Internet, thus with the dual firewall features of the firewall will help you reduce network security threats from the Internet.