Dynamic Host Configuration Protocol

Introduction

The Dynamic Host Configuration Protocol is also known as DHCP, It is a network management protocol used on Internet Protocol(IP), wherein Dynamically assigning an IP address to other network parameters so the device can easily communicate with other IP networks.  A DHCP server enables the device to request IP addresses automatically from the ISP(Internet Service Provider).

DHCP was created by the Dynamic Host Configuration Working Group of the Internet Engineering Task Force(IETF)

• Runs over UDP
•  Utilizing ports
  1.  67 – connections to the server
  2.  68 – connections to client
•  Extension of BOOTP (the protocol used for simple interaction)-
•  DHCP enhances the capabilities of BOOTP
•  DHCP is basically used for dynamic configuration
•  Uses client-server model

Objective of DHCP

• DHCP temporarily binds IP address & other configuration parameters to DHCP client & provides a framework for passing configuration information to hosts
•  DHCP was designed to provide computers with a temporary address
•  DHCP is well adapted to the situation where hosts move from one location to another or are routinely connected and disconnected
•  Thus DHCP is mainly used to simplify the installation & maintenance of networked computers.

Characteristics

Centralized IP address administration

• Backward compatible with BOOTP – therefore a host running the BOOTP client software can request a static configuration from a DHCP server
• Supports multiple servers
• Provides dynamic assignment
• Allows static assignment 
• Doesn’t interact with Domain Name Service (DNS)

Software Elements

    Client Software :

•  installed in client machines
•  to handle broadcast requests
•  for automatic IP acquisition & acquiring other configuration

    Server Software :

• installed in server machines
• designated to respond to client requests for IP address
• manage pools of IP addresses & related configuration

    Relay Agent Software :

• DHCP clients broadcast requests onto local n/w.

Terminology

DHCP Databases:

• The DHCP server uses two databases
  •  One database acquires IP addresses manually and binds them permanently to hardware addresses similar to BOOTP.
  •  Another database contains 1 or more blocks of IP addresses (address pools) that are dynamically assigned to clients on the FCFS basis i.e assigning on demand When the host no longer needs the IP address, it is released & returned.
• DHCP leases: DHCP issue a lease for a dynamic IP address that expires at the end of the lease time
• After 1⁄2 the lease time, client can renew the lease time
• DHCP leases: Once the lease has expired the client must either stop using the IP address or acquire a new IP address
  If more than 1 DHCP server, each may offer an IP address to the client & Clients can select the best offer.
  There are 3 types of address leases: manual, automatic & dynamic
  • Manual lease: N/W manager explicitly assigns all IP addresses
  • Automatic lease: DHCP server permanently assigns a specific IP address and dynamically assigns the rest
  • Dynamic lease: DHCP server dynamically assigns IP addresses for a specific period of time when a permanent address is not required.