3.4.1.1 Introduction to Window 2003 Server
3.6 DHCP SERVER
DHCP
(Dynamic Host Configuration Protocol) is a protocol that allocates IP address to computer on a network. DHCP centralized the management of IP address allocation and reduces human error associated with manual IP configuration. DHCP server supplies all the necessary networking param-eters. Two things are always handed out as a part of DHCP configuration: IP address and subnet mask. Further DHCP will frequently configure clients with optional values, such as a default gateway, DNS server address, and the address of a Window Internet Naming Server, if one is present. Scenario showing DHCP server IP address allocation.
3.6.1 Working of DHCP Server
(i) DHCP Scope (ii) DHCP Super Scope (iii) Exclusion IP Range (iv) DHCP Lease Time (v) IP Reservation DHCP Scope
Scope having the range of IP address for providing dynamic IP address to other computer. A group of IP address within a scope is called as DHCP scope.
DHCP Super Scope
A super scope is used to combine two or more scopes each serving different subnets, and can make the administration of several scopes on window 2003 DHCP server more manageable. Using super scope you can group multiple scopes as a single administrative
entity that allows the client to lease from either one. With this feature, a DHCP server can:
• Support DHCP clients on a single physical network segment where multiple logical IP networks are used. When more than one logical IP network is used on each physical subnet or network, such configuration is called multinets.
• Support DHCP clients located on the far side of DHCP and BOOTP relay agent.
• In multinet configuration, DHCP superscope can be used to group and activate individual scope ranges of IP addresses used on your network. In this way , a DHCP server computer can activate and provide leases from more than one scope to clients on a single physical network.
Exclusion IP range
If you want to reserve some IP for any computer i.e if we want that from the series of 192.168.0.2 to 192.168.0.100 if we want that a series of IP addresses must not be assigned automatically then at can be done using exclusive IP range.
DHCP Leased Time
DHCP lease time is validity of IP address. By default DHCP lease time is 8 days minimum,1 day maximum 999 days, 23 hours to53 day.
With in 8 days:-
After 80% of day clients demand new IP some times server refuse the client request. After 87.5% of days it will retry, and if the server did not give the new IP address then the client will receive APIPA address (Automatic Private IP Address).
When a DHCP client is unable to locate a DHCP server, the client picks out a random IP address from the private APIPA address range of 169.254.*.*, with a subnet mask of 255.255.0.0. The 169.254.*.* IP range is private because that network number is not in use on the internet, it is random because the client generates an arbitrary host number for that network.
The significance of APIPA is that DHCP client computers that cannot find a DHCP server can still be assigned an IP address and communicate with other computers on the same subnet mask that also cannot find DHCP server. It allows communication
when DHCP server is down or just plain not there. Note that APIPA does not assign a default gateway, and therefore it cannot communicate with any computer that lives on the other side of a router.
IP Reservation
There are some DHCP clients that you want to be the DHCP clients, but you will also want to make sure that they get same IP address every time. This can be done by statically filling the IP address. We can reserve IP address with the help of MAC address for a particular computer.
3.6.2
Installation Steps of DHCP Server
• start→ control panel
• add and remove program→ add and remove window components
• select networking services and click on detail button
• check box of DHCP server
• ok→ finish
3.6.2.1
Steps To Configure DHCP Server
• start→ program→ administrative tool
• select DHCP
• create new scope in action menu→ new scope → next
• give scope name→ next
• give IP address range→ next
• add exclusion name→ next
• check lease duration→ next→ finish
After DHCP server is configured, it is required to be authorized and DHCP scope should be active. For that select DHCP server and click on authorize in action menu. Then right click on scope name and click on active.
3.6.2.2
On Client Side
• Go to LAN card properties → select TCP/IP protocol→ properties
• Select obtain IP address automatically
• Go to command prompt (cmd)
• Give command
3.6.2.3
Backup of DHCP Server
We can take backup of all the configuration in DHCP server with the help of administrator. Backup means to export the DHCP database to another system, as it is helpful in case due to any reason our data is corrupted or deleted, we can take our database from the place where it is stored. Steps of taking backup :
• Stop the DHCP server and disable the DHCP server services
• Copy the DHCP server directory to a temporary location, say pen drive or on a new DHCP server.
3.6.3 DHCP Relay Agent
The DHCP relay agent is a software that listen DHCP discover packet and forward to DHCP server. In window 2003 server system the DHCP relay agent can be enabled as a part of Routing and Remote Access (RRAS).