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Network+ Study Guide (N10-003)

                                                                                               Index            

DHCP


DHCP stands for Dynamic Host Configuration Protocol and provides a solution that automatically assigns IP addresses to computers on a network. When a client is configured to receive an IP address automatically, It will send out a broadcast to the DHCP server requesting an address. The server will then issue a "lease" and assign it to that client. The time period that a lease will last can be specified on the server. Some of the benefits of DHCP include the following:
 

 

  • Prevents users from making up their own IP addresses.
  • Prevents incorrect gateway or subnet masks from being entered by your helpdesk.
  • Decreases amount of time spent configuring computers especially in environments where computers get moved around all the time.
  • Handy in situations where you have a large sales staff that only have to work 1 day a week. On that one day they bring their laptops and they can just plug them into the network and they are all set.

DHCP clients will attempt to renew their leases when %50 of the lease has expired. The client will send a message to the server that assigned the lease. Assuming the DHCP server isn't on fire or anything it will return a message with the new lease. If the server is unavailable, then the client can continue functioning as it has %50 remaining still. The client will continue as normal until the lease reaches %87.5 used at which time it broadcast to all DHCP servers and attempt to get a new lease. If the client receives a rejection message or the lease expires then the client must start all over again and will get a different IP address. If the lease expires and the client is unable to get a new one then the user will not be able to communicate over the network.